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1. tl HH LM ili 11 __ i 2 daly im Dp emm TT ELT I i ____ 1 eee ee iem dalla abeo nin m 37 eee CIRCUIT DIAGRAM SK12750 ee GENI _ __ _ __ ______ ee eee n L LE I dl r o PPP ISSUE 4 5 3 4 5 4 4 5 6 4 57 4 5 6 mechanism allowing the CPU to read extension in the interface for microdrive and RS232 applications Links H and N shown directly above 1 5 allow a second source ROM to be fitted The Hitachi H and NEC N ROMs use different pins for the enable and select inputs pins 20 and 27 The links allow the inputs to be reversed accordingly Standard 16k RAM IC6 IC13 eight 16k RAM ICs making up the standard 16k x 8 bit RAM memory are organised as a matrix of 128 rows x 28 columns Thus separate 7 bit row and column addresses are reguired to access any one of the locations These addresses are supplied by the CPU on address bus 13 via an address multiplexer IC3 IC4 low order address bits A6 AO give the row address and are selected at the beginning of the memory access cycle when initially the RAS output from the ULA is high Later as2. EAR TAPE L INTERFACE TAFE MIS EXPANSION PORT Y Powth SUPPLY 12 ZX SPECTRUM BLOCK DIAGRAM FIG 1 1 1 3 259 4 1 4 2 4 3 4 4 4 5 4 5 1 4 5 2 Dynamic Memory Refresh The CPU incorporates built in dynamic RAM refresh circuitry As part of the instruction OP code fetch cycle the CPU performs a memory request after first placing the refresh address on the lower eight bits of the address bus At the end of the cycle the address is incremented so that over 255 fetch cycles each row of the dynamic RAM is refreshed This mechanism only applies to the optional 32k expansion RAM in the 48k Spectrum An alternative refresh method is adapted for the standard 16K RAM MEMORY ORGANISATION In the standard 16k Spectrum there are 32k bytes of addressable memory equallydivided between ROM and RAM The lower 16k bytes of memory addresses 0000 are implemented in a single ROM 1 5 which holds monitor program This program is a complex Z80 machine code program divided broadly into three parts one each covering the input output routines the BASIC interpreter and expression handling Details of the program content although outside the scope of this manual are referred to as necessary The upper 16 bytes of memory addresses 4000 7FFF are implemented using eight 16k bit dynamic RAMs IC6 ICI3 Approximately half of this space is ava
3. o Toor EENEN LL LU 5 Lr qua AAN NH T core X MAH m GER GENS ee Di ZX SPECTRUM ISSUE 2 FIG 1 4 CIRCUIT DIAGRAM ESK 12740 ISSUE 1 gb uH un cadi di ot mE 11 Le 1 14 unu n 14 B n 1 8 m i d E Ad 1 1 ur Ha y m aum 7 i m 1 241 1 uM w T TY t CI Lu E 0 dH m J CF iy i ___ UL n y di ps M aly u M ago aj NINS 8 LL M mE rida 16 URES n adt w Hoa US M M H a 1 n 1 th n n M 4 il Wo Fn ou M ii i i M 1 M L
4. 24 222 INTRODUCTION A block diagram of the complete ZX SPECTRUM micro computer is given in Figure 1 1 It is valid for all build standards fitted with either lok or 48k bytes of dynamic RAM memory Although functionally identical detailed circuit changes have been introduced to improve reliability and to assist with manufacture The printed circuit board layout has also been modified Details of these changes are highlighted where necessary in the following paragraphs and in later sections referring to fault diagnosis and repair ARCHITECTURE The architecture of the Spectrum shown in Figure 1 1 is typical of many microcomputer systems in that it comprises single microprocessor board in this instance LA 780 CPU a read only memory ROM an expandable RAM memory and an input output section handling the keyboard tape and TV display functions The latter is recognisable as the logic gate array ULA and the three functional blocks shown in the right of the diagram The computer is built on a single printed circuit board which also includes a regulated power supply fed from an external 9V power pack The keyboard matrix is part of the upper case assembly and is connected to the board two ribbon cables and A description of each section follows 1 1 3 1 3 2 222 3 4 R 3 0 3 7 3 8 Z80A CPU The 2904 is 8 bit single IC central processing unit CPU It is cloc
5. LOUD SPE AKER 1983 ISSUE 2 mannered 122 Sm FAL EJA LE C 45 1 2 Cha 270 44 zx SPECTRUM 44 S RC 121 6 du c cha R63 2 10 e 4 gt C e a 4 o 4 C42 ASS 1 MOD FIGURE 4 3 EXPANSION MEMORY IC LOCATIONS 4 21 HIGH ENABLE 19 11 IC 26 TI 4532 4 FIGURE 4 4 ISSUE 3 LINKS vs LOW ENABLE 14 4532 23 IC MANUFACTURER AND TYPE TA MA 12 746 ISSUE COMPONENT LAYOLT SZ LEE up d i 1 PRINTED CIRCUIT BOARD ISSUE 2 FIG 51 Et HE SECTION 5 PARTS LIST oub Section LIST OF CONTENTS Page No Introduction 5 1 Notes to Table 5 2 5 1 1 1 2 INTRODUCTION Parts lists for the ZX SPECTRUM are provided in table form one for the case assembly Table 5 1 and another for the board assembly Table 5 2 latter covers the Issue 2 and 3 Spectrums and is related to the board layout diagrams given in Figure 5 1 and 5 2 Table 5 2 also lists the alternative components which the service engineer will occasionally find on production versions of the Issue 2 board or may introduce retrospectively in order to improve performance These components are listed
6. ZX SPECTRUM a careful physical examination of the board can sometimes indicate an obvious fault Burst out discrete components or an overheated track show up ois as do the attentions of an enthusiastic amateur Bearing in mind the latter short circuits caused by hairline solder splatter several ohms resistahce can cause some very misleading fault symptoms Provided first principles are adhered to and a common sense approach is adopted it will be found after a short space of time that fixing a faulty Spectrum is very much a routine operation 4 6 2 2 2 3 Power Supply Unit Ihe unstabilised external power supply unit 15 source of some problems The design is such that at minimum input voltage 215V a c and 1 4A output the voltage trough should not be less than 7 0V at maximum input voltage 265V a c and 60QmA output the voltage peak should be less than 13V Initialisation At switch on the computer should automatically initialise and produce a clear screen with the statement 01982 Sinclair Research Ltd displayed in the lower left section of screen This indicates that most of the system is working If the Spectrum does not initialise carry out the following basic checks Basic Checks It 15 difficult to be specific in a fault finding guide because of the large variety of fault conditions which can occur but the following procedure starting with a table of checks set
7. i MREQ AIS 1C2310 1 23 3 RAS c23 8 0 ADDRESS SELECT LOW ORDER HIGH ORDER 1 1C23 6 CAS T DELAY FIG 12 EXPANSION RAM RAS CAS TIMING READ CYCLE SHOWN 1 7 25252 229 5 2 4 352 9 5 2 6 5 3 1 Using the 14 MHz clock the ULA derives line and field timing compatible with the external TV receiver Video is derived by accessing the memory mapped display area in the RAM in a set seguence at set times throughout the picture frame The addresses are necessarily independent of the CPU and appear on the ULA address lines A6 through AO as two separate bytes timed by the RAS CAS row column address select lines The net result is three separate video waveforms outputs from the ULA on pins 15 16 and 17 These carry the luminance signal Y incorporating the line and field sync and two unmodulated colour difference signals U and Y making the Spectrum compatible with both colour and monochrome receivers From the ULA the colour difference signals are applied to the colour modulator IC14 via two level shifting networks These match the ULA output levels with those reguired at the B Y and R Y inputs to the modulator In the Issue 2 Spectrum the level shifting network is passive incorporating two potentiometers VR2 These are reguired to set up the chroma bias level on 1 14 pin 3 such that the voltage difference measured betwee
8. 68R TRANSISTORS Circuit Reference TRI TR2 TR3 TRA TRS TR6 TR7 TRS TR9 MISCELLANEOUS Reference REG MOD Loudspeaker Modulator Screen Insulator Heatsink Regulator Fixings l ODT OIL OILL SKI Issue 2 Issue 2 Mod ZTX313 ZTX313 ZTX650 TIPP31 ZTX213 ZTX313 Description 5V regulator UHF Modulator with E36 vision carrier UK only 40 ohm T V Type Special Issue 2 or 3 Screw 2 Washer shk prf 4BA 3 Nut hex ABA l6 way 10 off for 48k expansion RAM 14 2 off for 48k expansion RAM 28 way for ch hd 4BA 15 16 Notes Issue 3 ZTX313 ZTX313 ZTX650 ZTX213 5 ZTX313 ZTX450 BC184 Manufacturer Part Number 7805 Astec UM1233 1740 in lok model only lok model only GENERAL DATA Earliest version very pale brown keys Second version grey keys Third Fourth versions grey keys but heatsink now visible through the edge connector slot Early Spectrum plus same as fourth type Dissembly after removing the screws tilt back face up and carefully lift the top taking care not to break any of the keyboard tails Heatsink when operating computer with the heatsink removed to obtain access a temporary heatsink must be used made of anything as long as it fits under regulator Circuit Diagram idealised version on centre pages shows all modific ations which should be made Note
9. However during the execution of a BEEP instruction the CPU writes instead to port 254 on data bus 4 This effectively boosts the MIC output driving the loudspeaker so that the BEEP tone can be easily heard During the execution of such an instruction the cassette recorder is not running so there is no conflict at the MIC EAR sockets 1 10 6 6 1 6 2 6 3 POWER SUPPLIES The on board power supply unit receives a 9V unregulated supply from the external Sinclair ZX power pack and derives the following internal supply rails a regulated 5V for the IC logic circuits ULA and the UHF modulator b 5V and 12V for the standard 16k dynamic RAM c 12V for the colour modulator circuits The external power pack incorporates a mains transformer full wave rectifier and capacitive smoothing A thermal fuse is fitted at the transformer input The on board power supply unit incorporates a 7805 regulator deriving 5V power rail and an inverter stage TR4 TR5 The latter raises the level of 9V unregulated supply to in excess of 12 The resultant sguare wave at the junction of TR4 collector and inverter coil is subseguently rectified and smoothed by D5 C44 producing 12V output for the RAM Additional smoothing imparted by R62 C45 produces the 12V supply for the TV circuits free from noise generated by the RAM The sguare wave at TR4 collector also supplies the Zener rectifier diode combination DI6
10. a b A modified layout of board i e Issue 1 Issue 2 and Issue 3 Issue 1 This layout allowed for the 16k RAM to be mounted direct the board with the 32k extension consisting of a subsidiary board mounting onto special connectors Approximately 26 000 units were manufactured Issue 2 This layout allows for all 48k of RAM to be mounted direct on the board sockets ready for a memory update are fitted on 16k versions small number of Issue 2 units were manufactured using disc capacitors for 47 pF and 100 values but subseguently axials were introduced Issue 3 This layout incorporates advanced circuitry for the colour tuning removing the need for potentiometers and trimmers and the associated adjustment It also allows for OKI ICs to be used in the 32k extension memory The heatsink is also redesigned and is relocated at the back of the case The Ferranti ULA type 5 102 plus spider addition replaced by ULA type 5C112 5 102 This ULA has a timing fault which was cured by connecting 74500 IC mounted on a miniature board and spider This was fitted to approximately 40 000 units 5C112 This improved ULA has no spider modification but has either diode or resistor or transistor connected to 1 The details are Diode resistor mod 4k7 resistor from 12V to pin 30 on IC2 and diode IN 4148 from pin 30 of IC2 to pin 33 of ICI Transistor mod TR6 ZTX313 connected as follows Base 10
11. b 22 Pin 4 RAT Pin 3 WITE Pin 15 If no fault has been found and the computer still has not initialised the fault could lie in the RAM the computer is a 48k machine the 32k of expansion RAM can be isolated An easy way of doing this assuming that ICs are not fitted into sockets is to remove the 5V from 1825 This is probably best done by very carefully cutting the track to 1825 pin 16 If this operation clears the fault condition the expansion RAM will have to be further isolated In either instance the point has been reached where it is necessary to start replacing ICs Where the fault persists after isolating the 32k expansion RAM it would be necessary to start changing individual ICs in the order of to 6 RAM ULA IC2 Z80A After each change of IC the unit must be powered up to check for correct initialisation A method of fault finding that can be used on both the 16k and 48k versions is to make up a test IC device This may be done by using an IC test clip to which is attached a serviceable IC of the relevant type e g 4116 or 4532 to bridge across each suspect in turn This method is not guaranteed to work but can often save a lot of time unnecessarily changing suspect ICs Memory Check Where a Spectrum has initialised correctly but a RAM memory fault is suspected it is possible to find the faulty address and relate it to a faulty IC by carrying out the following pr
12. for SINCLAIR RESEARCH LTD MARCH 194 Sinclair Research Ltd 1 INTRODUCTION This manual is for use by authorised SINCLAIR dealers engineers and representatives as a guide to rectifying faults on the SINCLAIR ZX SPECTRUM personal computer The manual refers principally to the Issue 2 and Issue 3 Spectrums but provides a background to the Issue 1 version in the section dealing with modification history Basic knowledge of ZX SPECTRUM operating procedures is assumed as is knowledge of current workshop practice relating to microcomputers NOTE Essential modifications are required on some Issue 2 Spectrums Refer to Modification History Section 4 and implement necessary SAFETY MEASURES This ianstruction manual contains certain WARNING and CAUTION notices which MUST be followed by the user to ensure SAFE operation and to retain the equipment in a SAFE condition Any adjustment maintenance and repair of the opened apparatus under voltage shall be carried cut only by a skilled person who is AWARE OF THE HAZARD INVOLVED SECTION 1 SYSTEM DESCRIPTION Sub Section LIST OF CONTENTS Page No 1 Introducbion ne 2 Architecture 3 780 CPU 4 Memory Organisation 1 4 Read Write Operations 1 4 5 Input Output 1 6 TV Picture Generation 1 6 Keyboard Scanning 1 8 Tape Interface 1 10 6 Power Supplies 1 11 Circuit Diagrams ZX Spectrum Issue 2 Fig 1 4 ZX Spectrum Issue 3 Fig 1 5
13. DI2 generating 5V for the RAM and is available at the expansion port for use by peripherals The 12V 5V and 5V are also made available SECTION 2 DISASSEMBLY ASSEMBLY Sub Section LIST OF CONTENTS Page No Disassembly Assembly 2l 11 1 3 2 1 2 7 DISASSEMBLY Unplug all input output leads and turn the computer upside down to reveal five self tapping screws Remove the screws Hold the two halves of the case together and return the computer to the keys uppermost position The top half of the case can now be separated from the bottom half although it remains connected to it by two flexible keyboard ribbon connectors Care should be taken not to damage the ribbon connectors As an aid to reassembly the lie of the connectors within the case should be noted remove the board from the lower half of the case remove one self tapping screw adjacent to 1822 socket and lift out the board It may be advantageous to make up two short pluggable extensions for the keyboard connectors in order to improve accessibility to the board To change either the keyboard membrane or the rubber keyboard mat it is first necessary to remove the escutcheon plate template This is attached to the case by double sided adhesive tape around the edges The template is removed by inserting a screwdriver at one end and levering it away from the case It 15 not normally possible to remove the template without damage ASSEMBLY A
14. IC2 pin 30 Emitter to ICI pin 33 Collector to IC2 pin 1l 60001 This alters the timing of the colour burst signal and improves the performance of the Spectrum with certain television sets e g Hitachi Grundig It also causes the screen picture to be shifted by one character width to the left NOTE The values of certain components vary depending on which board and which ULA is used as follows 4 3 1 3 Board Issue No 2 2 3 SOULS 0 001 0 001 Component R47 220 Ik Ik R49 8 k2 10 k 10 k R56 220 n 470 fi Ik R63 220 n 470 n Ik Modifications Issue Board A number of modifications were introduced and these should be checked for and if necessary introduced retrospectively a b d f g h 100 pF capacitor between RAS and ground necessary only when using 5 02 470 pF capacitor between IC2 pin 28 and ground required only when IC2 and RAM ICs are all of NEC manufacture resistor between RAS and 23V and resistor between CAS and 12V only when RAM ICs are of National manufacture R57 3300 must be removed and the 470 pF capacitor 15 not required 47 resistor between pin 13 of LMI889 and ground required only if the difference between white and yellow colours is inadequate If disc capacitors are used for C41 and C49 47 nF they must be replaced by axial components Capacitor C46 1 uF electrolytic should be replaced b
15. Integrated Circuits Link Settings For both the Issue 2 and the Issue 3 boards the memory upgrade is accomplished by plugging four logic ICs and eight memory ICs into existing board sockets Depending on the types of memory IC used appropriate circuit links must be fitted on the board Figure 4 3 shows the layout of the area of the board containing the empty sockets The Issue 3 board is shown which also gives positions top left of diagram of the links 4 19 4 2 Issue 2 Board The ICs used on this board NOTES are as follows ICIS 1222 TI 4532 3 or TI 4532 4 200ns 25005 IC23 141 532 24 1741500 25 26 7415157 National Semiconductors 1 external RAM ICs must be of same type 1 all 3 or 4 variants 2 3 on the board IC26 pin 10 should be fitted if ICI5 IC22 are type 4532 3 3 LINK 4 should be fitted if 5 22 are type 4532 4 3 Issue 3 Board The ICs used on this board are as follows NOTES IXPE IC15 1022 4532 3 TI 4532 4 or MSM3732 200 ns or 250ns IC23 741532 IC24 74LSOO IC25 26 7415157 NOT National Semiconductors 1 All extension RAM ICs must be of the same type 2 Two links must be fitted on the board grid located between edge connector and m c jack socket depending on memory manufacturer and type high or low enable See Figure 4 4 for link positions vs manufacturer and IC type 4 20
16. RAM failure as already described If RAMS are O K or fault is more serious and RAMS cannot be checked then check if the 5v supply is reaching all I C s in order ICI 2 24 23 3 4 26 25 and 5 Replace the open circuit component cutting off the 5v supply if this is the case Faulty or missing sound usually identifies the ULA as being faulty and this 1 most likely suspect in any case Flick the clock crystal with your finger this will guickly determine if it is faulty or not Although I C s are best checked out systematically using a logic probe or even a scope it is worth noting that after ICI the most likely culprits are IC2 and 105 neither of which are particularly reliable and it may even be worth replacing the three automatically as a fast check 12 PERMANENT CHECKER FOR LOGIC PROBE USE If a logic probe is available it is well worth making a table of the results of checking each pin with a good computer switched on with keyboard disconnected Thus when any computer is being tested all that is needed is to compare the readings with your correct set and different readings will quickly pinpoint the faults 13 FLICKERING WHITE BACKGROUND MAY BE CAUSING EYESTRAIN If resetting the computer doesn t help which is not uncommon if a CIV is being used then the only thing is to set up the computer to display a coloured background with white printing see spectrum manual for this but green 15 the
17. RAM location the first fault identified will have to be repaired before it is possible to proceed 4 9 250 Keyboard Structure The keyboard is connected horizontally in eight blocks of five keys ewn 1 e foh y hime sshaws tthe fault is with circuitry or the 8 way membrane and that if any block of eight keys fall the fault is with KBl circuitry or the 5 way membrane Possible keyboard faults are listed in paragraph 2 60 KB1 2 3 4 2 4 5 e KB2 un 3 CAPS SHIFT ENTER SYMBOL SPACE SHIFT M 1 d T e FIGURE 4 1 KEYBOARD FORMAT 4 10 2 6 Fault Finding Guide As with any complex digital equipment the possible fault permutations are vast thus the following table is not intended to be an exhaustive list of the faults that might occur on the Spectrum It is intended as a guide only to possible courses of action to follow when faults show up in particular areas of the circuit These areas are listed in the table with sub headings in no particular order of priority It is envisaged that the ZXTP test tape has been loaded or an attempt has been made to load the tape in order to check for a faulty condition AREA SYMPTOM ACTION TV screen dead TR4 base collector Remove TR4 smoke appears on shorted switch on Short persists with 1 Check TRS and C44 TR4removed 2 Visually check track 3 C
18. according to keys in error If the entire keyboard is non functional then check 5v supply 15 reaching it before replacing ULA Probably the commonest fault lies with a faulty 10K resistor R65 to R69 easily identified according to which keyboard co9lumn 15 faulty 8 VARIOUS FAULTS WHICH APPEAR ONLY WHEN WARM Check heatsink thoroughly heatsink is then the ICl will be the cause has been replaced before it may be worth adding extra heatsink for it See also following symptom 9 INTERMITTENT FAULTS If such faults show up with a comoaritively new Spectrum then it is most likely that they are due to poor contacts soldering during the manufacturing process Check all holders and pins for tarnish and dry joints Replace faulty holders by cutting them out and replacing completely Check after this for poor contacts or loose contacts look for items which have been poorly soldered or even where soldering has been omitted Finally check the boards for hairline cracks and breaks especially radiating from heatsink screws 10 TEXAS SNI889 INSTEAD OF LHA889 A few models appeared with the SN version and these may even have been used as replacements during repairs Although unlikely to find now if SN types have been used replace completely by LH type POWER SUPPLY COMPUTER NOT WORKING CORRECTLY If computer is functioning at all check for single RAM failure then multiple
19. and repair of the ZX SPECTRUM It is assumed that users have a reasonable knowledge of electronic servicing theory and standard fault finding techniques and have access to the test equipment and tools required to carry out the task The table below contains a list of the minimum recommended test equipment and materials EQUIPMENT SPECIFICATION MANUFACTURER Oscilloscope with Oscilloscope probe x10 0 02 us cm Rise Time Variable power supply unit to 30V d c Mono cassette recorder With RECORD and PLAYBACK facilities Mains extension lead Safebloc type Multimeter Colour Television ZX Printer test tape Blank tape General purpose Open Market Sinclair Open Market 12mm and 6mm wide Tesafix 959 Double sided adhesive tape B D F TESA or 3M equivalent Engineers who are already familiar with the Sinclair ZX81 will find some Similarities in ZX SPECTRUM The Spectrum however is a more sophisticated device with colour and sound circuitry The ZX SPECTRUM is supplied with either 16k or 48k of on board RAM The lok version is wired so that it can be expanded to 48k by the addition of a number of appropriate plug in ICs For details of the memory upgrade see sub section 4 of this section See Section 5 Figures 5 1 and 5 2 for the layouts of the Issue 2 and Issue 3 boards respectively 4 2 1 2 Modification History Two major modifications have been implemented on the Spectrum boards
20. cycles i e most rows are refreshed each time ULA accesses the memory mapped display area during picture compilation remaining rows are refreshed as a result of other read cycles also known to occur at regular intervals within the refresh period 1 5 4 5 9 4 5 10 4 5 11 5 1 5 2 5 2 1 32k Expansion RAM ICI5 IC32 The eight 32k ICs making up 32k x 8 bit expansion RAM are in fact 64k ICs with either row or column drop out rendering one half of the memory non functional In order to accommodate the Texas Instruments RAM Type TMS 4532 or the optional OKI RAM Type MSM3732 a set of links are provided visible on the circuit diagram above the address multiplexer IC25 IC26 These links not only cater for the different manufacturer Issue 3 Spectrums only but also allow in both instances one of two IC versions to be selected depending on which half of the RAM top bottom left or right is functional The links are respectively TI and OKI manufacturer Issue 3 Spectrums only 3 4 TI version and H L OKI version Issue 3 Spectrums only NOTE It is essential when replacing ICs in this area that all RAMs carry the same manufacturers part number and that the links are selected accordingly The expansion RAM is organised as a matrix of 128 rows x 256 columns RAMs or 256 rows x 128 OKI RAMs Thus separate 7 8 bit row and column addresses are required to access any of these locations Thes
21. most relaxing background Save this programme and load it every time Spectrum 15 not being used for games 14 SPARE PARTS SUPPLIERS At time of printing the most popular suppliers appear to be CPC Electronic Components 194 North Road Preston Lanes PV Tubes 104 Abbey Street Accrington Lanes BBS This list may be amended in future printings NOTES
22. version only 60 68 0 ar 0 38 version 4 eeanec hse pis Texas Toes Ta resa 3732 09 Early circuit showing presets TC2 and VR2 to match the early type boards 144148 835 935 X4 n TC2 64 65 Note the different pins 16 17 setup from Id in the generalised circuit diagram shown modulator 853 in the middle pages from fay fine In very versions instead of TRO somewhat unreliable resistor diode to 723 T was used which should be modified ING HE as shown in the centre pages TRS This very unreliable circuit was used in very early versions from pin 32 to base of Id This circuit should be modified to that shown in the centre 161 pages if not already done Modifications associated with 3 NO COIL BUZZ FROM INVERTER 5V ABSENT From symptom 1 it should be obvious that TR4 ZTX650 15 very prone to damage and this symptom is a sure indication that TRA must be replaced How ever before replacing the TR4 check the 21 213 using a transistor tester is O K and the coil since it is not unknown for all three to have gone at the same time and if only the TR4 is replaced it can fail again immediately if the others are faulty Whether or not these three are faulty or not there can be one or more faulty R
23. yF 22 yF 10 10 80 Elect C51 C52 C53 150 150 25V 10 Ceramic C54 470 25V 1090 C55 C62 47 nF 47 nF 25V 10 Ceramic C63 47 pF 47 pF 25V 10 Ceramic 64 IOOpF IOOpF 25V 10 Ceramic C65 IOOyF 22 yF 2 22 yF 20 10 80 Elect C66 47 nF 47 nF 25V 10 Ceramic C67 4 25 10 C68 C71 IOOnF 25V 1090 Ceramic CI2ICTS 16 pF 25V 1090 Ceramic C74 4 7WF 3 4 7uF 5V min Elect C75 IOOnF 25V 1090 Ceramic TC1 TC2 C76 47 nF 25V 10 Ceramic C77 7 IOOnF 25V 1090 Ceramic COIL Circuit Issue 2 Issue 2 Notes Issue 3 Rating Manufacture Reference Mod Tol Type Coil SPECTRUM SPECTRUM 1703 Duo CONNECTORS Reference Description Manufacturer Part Number EAR 3 5 mm jack socket MIC 3 5 mm jack socket PWR 2 1 mm co axial socket 5 ribbon connector Molex 5229 05CPB KB2 8 way ribbon connector Molex 5229 08CPB CRYSTALS Circuit Issue 2 Issue 2 Notes Issue 3 Manufacture Reference Mod Type XI 14 000000M Hz Note 14 000000MHz X2 4 433619MHz 6 4 433619MHz DIODES Circuit Issue 2 Issue 2 Notes Issue 3 Manufacture Reference Mod Type D1 D9 IN4148 1 4148 Signal D10 IN4148 Signal D11 D13 IN4148 IN4148 Signal 014 144148 4 Signal 015 157 157 Rectifier D16 5V 5V1 Zener INTEGRATED CIRCUITS Circuit Issue 2 Issue 2 Notes Issue 3 Manufacture Reference Mod Type ICI ULA 5C102 5C112 1 6C
24. 0001 Ferranti IC2 CPU 2780 7780 Z80A M780 741 5157 741 5157 Not National 1 5 SPECTRUM SPECTRUM SPECTRUM NEC Hitachi IC6 IC13 4116 4116 150 ns IC14 LM1889 LM1889 IC15 IC22 TI4532 T14532 48k only Texas MSM3732 OKI 123 7415323 7415323 48k only IC24 74LSOON 74LSOON 48k only IC25 IC26 74LS157N 7415157 48k only Not National RESISTORS 1 4W 5 unless otherwise stated Circuit Reference RI R 9 16 R17 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R33 R34 R35 R36 R37 R38 R39 R40 R41 R42 R43 R44 R4B R46 R47 R48 R49 RBO R61 R52 R53 R54 R55 R56 R57 R58 R59 R60 R61 R62 R63 R64 R65 R69 R70 R71 R72 R73 R74 R75 R76 R77 R78 VRI VR2 Issue 2 470R SK2 330R 3K3 180R 680R 10KO IKB IKO 220KO 100R 680R 156 10KO 680R 1KO 3K3 3K3 1KO IKB IKO 3KO SKI IKO 220 4K7 8K2 8K2 2K2 390R 100K 56R 220R 330R IKO 8 100R ISR 220R I5R 10KO 220R 47 18 2 Mod 1KO 1KO 2K2 10KO 4K7 470R 270R 470R IKO Notes 4 1 2 1 2 1 3 7 1 Issue 3 470 8K2 330R 180R 470 10K 10K 10K 220K 100R 680R I5R 10K 680R IK IKO 3KO IKO IKO 2K2 10KO 4K7 2K2 390 100K 56 IKO IKO 8 270R I5R IKO I5R 220 10KO 1KO 10KO IKO 470R Rating Issue 3B Tol 1 2 IW 2 2 2 2
25. 4 4 1 Renewal of components should be carried out using recognised desoldering heatsinking techniques to prevent damage to the component or to the printed circuit board Other points to be noted are a When replacing keyboard matrix take care that the ribbon connectors are fully inserted into the board connectors and are not kinked during insertion b Make sure there is good contact made between the voltage regulator body and the associated heatsink in order to ensure adequate heat conduction heatsink hole in certain Issue 3 boards allows excessive play which could cause fouling of the edge connector Take care in re assembly that the heatsink is fitted away from the edge connector c When the regulator is being replaced it is recommended that a suitable proprietary thermal grease is applied to rear surface of the component body d The modulator should be replaced as a complete unit When replacing plug in ICs it is advisable to use the correct removal and insertion tools Avoid contaminating the connection pins by hand ing f When handling ICs take normal anti static precautions It is recommended that only a suitably earthed low power soldering iron be used g After any component has been renewed the circuit board should be examined carefully to ensure that there are no solder splatters which may cause short circuits between tracks or connector pins lok TO 48k UPGRADE
26. 9 ICI 117 1 12 21 115 213 Where 170 is poked in 115 faulty gives 171 6 158 ICI7 174 ICIS 162 9 186 1020 138 1021 234 1022 42 3 NO COIL BUZZ FROM INVERTER REG7805 OPEN CIRCUIT Before replacing the 7805 check the heatsink to see if faulty or badly fitted Remedy physical defect in print or damage around screws Also check the TR4 5 and coil 6 CONTINUAL FAILURE OF POWER SUPPLY TRANSISTORS Ensure that all modifications have been carried out and that the edge connector is and not loose or damaged Check for proper fitting of all peripherals and verify that owner is not persistently inserting removing any of the add ons etc while the computer is switched on Note that many users are apparently incapable of grasping this simple point Check the plug sockets and cable if not suitable then replace with correct ones Check the mains and possible interference from other items on same circuit If satisfied then check if the Ov is correct on earth Monitor the Ov while running computer as this nay shew up an intermittent voltage fault A systematic check on all capacitors resistors to earth should find the culprit for this uncommon cause 7 KEYBOARD FAULTS It 15 recommended that keyboards are better replaced completely since they take a lot of battering and replacement is guite inexpensive If it 15 decided that the keyboard is worth repairing then tha diagram will show which tail is faulty
27. AMS as well caused possibly by the same forcing in interface during switch on all else has been fixed switch on and check if any RAM gets hot replace any very hot RAMS either in basic set or in extra board as this is a sure sign of being short circuit open circuit the guickest way to check is to bye pass each RAM in turn using a RAM known to be O K When so doing the same RAM must be used as the suspect and it should not be removed after each check for some ten seconds after each switch off or it will fault itself Use of a scope or logic probe is clearly a better alternative if available Tandy m tke a good inexpensive logic probe 4 DIRECT CHECK FOR A SINGLE FAULTY RAM Type PRINT PEEK 2373242560 PEEK 23733 CR If computer RAMS the reply is either 32767 or 85535 if less than either this means that there is a shortage of available RAMS thus one or more RAMS may be faulty Call the reply and if POKE N 1 85 CR then PRINT PEEK CR 15 typed the reply should be 85 RAMS O K in that case type POKE N 1 170 then PRINT PEEK CR when a different number to the 170 you have just poked into that address will be printed 85 and 170 are the easiest binary numbers 01010101 and 10101010 to cover all combinations in an 8 bit chip Where a different reply is given to either POKE locate the incorrect 1C as follows Where 85 is poked in faulty gives 84 IC7 87 IC8 81 IC9 93 6
28. IFT key is pressed row one output drives data bus DO high and so on The seguence ends with I O address 7F when column 8 is addressed In this instance operation of the SPACE key drives DO high Clearly the keyboard scanning routines make the distinction between the CAPS SHIFT and SPACE key by knowing which address line is being driven Tape Interface When LOADing or SAVEing programs using a cassette recorder ULA transfers information between the MIC and EAR sockets and the data bus performing A D and D A conversions as reguired Since the LOAD and SAVE functions are mutually exclusive a single pin on the ULA i e pin 28 is used both for input and output Separate I O read write cycles to port address 254 configure the pin accordingly During the LOAD operation the CPU executes successive I O read cycles reading the EAR input off data bus 6 When performing SAVE operation the CPU executes successive I O write cycles this time writing data to the MIC output via data bus 3 To ensure that I O cycles are correctly implemented the IOREQ line supplying the ULA is gated with address line AO via TR6 Thus if any memory transactions occur where AO is high not port address 254 then the IOREQ input is forced high inhibiting any attempt to perform an I O cycle Loudspeaker BEEP Operation It should be noted that while SAVEing the level of the MIC output is barely sufficient to drive the loudspeaker via D9 and TR7 010
29. Passed message not flashing Reduced memory size Keyboard does not allow loading Program fails to load Program appears ACTION 1 Change ICI 2 Carry fault finding procedure paragraph 2 2 Change 4 Carry out fault finding procedure paragraph 2 2 Chan5e Perform memory test 2 Change ICI See keyboard faults 1 Check jack sockets are fully inserted 2 If loading border are wide check D13 stripes in unusually 3 Check change Check Change IC2 401 NORM 0 680 100nF MIC EAR KO l nF Q 0v 5V AA FIGURE 4 2 SPEAKER LOAD INPUT WAVEFORMS 4 1 Pin No NOTES TABLE 4 1 4 IML889 PIN SIGNALS Signal CHROMA LEAD SINEWAVE BOOmV 0 2 5 d c 9 5V R Y INPUT 130 pS 65 pS CHROMA BIAS 4 8V 9 J de csv QV GROUND VIDEO INPUT d c 12V unreg CHROMA SUBCARRIER dc 122145 1212512 tyS pS REPETITION 65ms SUPPLY SOUND TANK LINKED d gt c CHROMA SUPPLY CHROMA OSCILLATOR OUTPUT SQUAREWAVE 0 2 us 4V PP D C 0 8V CHROMA LAG SINEWAVE BOOmV PP 2 uS 95 Not Connected 1 Rails and signals taken on switch on computer displaying Sinclair1 y 2 No keys pressed 3 All d c levels positive wrt OV 4 18 3 3 1
30. a memory location or I O device the control signals discussed so far are active low tri state outputs The control signal described here 15 the interrupt last maskable INT This input is active low and is generated by the ULA once every 20 ms Each time it is received the CPU calls the maskable interrupt routine during which the real time is incremented and the keyboard is scanned CPU Clock Returning to the CPU clock mentioned earlier in this section the ULA 15 able to inhibit this input bringing the CPU to temporary halt This mechanism gives the ULA absolute priority allowing it to access the standard 16k RAM without interference from the CPU see RAM description Switching transistor TR3 ensures that the clock amplitude is 5V rather than some arbitrary TTL level This is essential if the CPU is to operate effectively while executing fast machine code programs of the Space invader 1 2 CLOCR POAT 1 15 SELECT READ WRITE AGOAESS MULTIPLEXER CONTROL MULTIPLEXER 162526 12 23 34 1 6 MICROPROCESSOR KEYBOARD AM iiA T EH ROM 0000 3FFF 4 Logie ahi CASI COLOUR MODULATOR d t IFEF 0000
31. ctor and the jack socket Again the extra memory is obtained by plugging in 4 logic ICs and eight memory ICs Hitachi vs NEC ROM During manufacture wiring links are selected and inserted in the board according to whether a Hitachi or ROM is used These links are marked and N as appropriate and are located as follows Board Issue between the ROM and the heatsink Board Issue 2 beneath the raised portion of the heatsink Board Issue 3 adjacent to the loudspeaker Clearly if the ROM is changed for one of a different make then these links must be changed as well FAULT DIAGNOSIS Techniques In a closed loop system such as a computer because of the inter dependence of numerous component parts fault diagnosis is not necessarily straight forward addition because of the high speed cyclic operation interpretation of any waveforms on control data and address lines as being valid depends to a large extent on practical experience of the system There are however certain checks with valid waveforms and levels that can be carried out before substituting any integrated circuits Experience has shown that the best method of initially checking waveforms and levels can be to compare with the same point in a known serviceable board The following pages provide a basic fault finding procedure and furnish a list of possible faults along with suggested ways of curing them With a densely populated board such as
32. d Upper Case Moulded Lower Case Keyboard Mat Rubber Keyboard Membrane N F I Keyboard Template Rubber Feet Self Tap Screws case fixings 5 off Double sided adhesive tape 12 mm wide Tesafix 959 B D F Tesa Double sided adhesive tape 6 mm wide Tesafix 959 B D F Tesa self Tap Screw board fixing 5 2 Wh ou w ouod uH uum ISSUE FIG 5 2 COMPONENT LAYOUT OSK12756 PRINTED CIRCUIT BOARD ISSUE 3 TABLE 5 2 BOARD ASSEMBLY Circuit Issue 2 Issue 2 Notes Issue 3 Rating Manufacture Reference Mod To Type CAPACITORS Unless otherwise stated all capacitors are axial types 1 8 47 nF 47 nF 25V 10 Ceramic C25 22 yF 22 yF 10V 10 80 Elect C26 47 nF 47 nF 25V 10 Ceramic C24 yF 1 yF 50 10 Ceramic C28 22 yF 22 yF 10 1090 8090 Elect C29 C30 47 nF 47 nF 25V 1090 Ceramic C31 C32 IOOnF IOOnF 25V 1090 Ceramic C33 47 nF 47 nF 25V 10 Ceramic C34 22 yF 22 yF 10V 10 80 Elect C35 10 nF 10 nF 25V 10 Ceramic C36 47 nF 25V 10 Ceramic C37 C38 33 pF 33 pF 25V 109 Ceramic C39 10 nF 10 nF 25V 1090 Ceramic C40 C42 47 nF 47 nF 25V 10 Ceramic C43 IOOnF IOOnF 25V 1090 Ceramic C44 C45 IOOyF IOOyF 16 10 80 Ceramic C46 1 yF 1 50 10 80 Elect C47 22 yF 22 yF 10 1090 8090 Elect C48 47 nF 47 nF 25V 10 Ceramic C49 47 nF 7 47 560pF 25V 10 Ceramic C50 22
33. e addresses are supplied by the CPU on address bus Al4 AO via an address multiplexer 1 25 1 26 For example when accessing the TI RAM the low order address bits A6 to AO give the row address AR is held low on the 3 version selecting the top half of the memory and high on the 4 version selecting the bottom half The column address is given by the high order address bits 14 Row column address selection and RAS CAS timing for the RAM is decoded in IC23 IC24 from inputs supplied by the CPU i e address line 15 selecting addresses 8000 upwards and MREQ heralding a memory read or write cycle theoretical timing diagram illustrating the RAS CAS waveforms is given in Figure 1 2 INPUT OUTPUT The input output section of the Spectrum is centered round the ULA ICI The functions performed within the device include TV video compilation keyboard scanning and tape input output It also derives and controls the CPU clock lt j gt CPU using an external 14 MHz crystal XI and drives the loudspeaker when a instruction is being executed Each of these sections and the supporting circuits are described below TV Picture Generation The video compilation section of the ULA operates in conjunction with the memory mapped picture display area in the standard 16k RAM the colour chrominance modulator ICI4 and the UHF modulator This combination produces a high resolution 24 line x 32 character eight colour TV display 1 6
34. heck TRA blows again l Change TR4 and TRS even though TR5 checks out 24 Check that TR5 circuit components are to latest specification Not initialising No C 1982 Follow fault finding ore paragraph 2 2 No video No video 1 Change ICI 2 Check TRI and TR2 NOTE Table 4 1 No video after 1 Visually check and sets out typical ULA changed socket signals found on 3 Check for shorting ICIA pins 1 18 between C65 and R53 4 pins 1 18 4 Carry out fault finding procedure para 2 2 above Check voltage drop across R64 2 Check 45V regulator 0 and 9V regulator I P 3 Check PWR socket not shorted 4 Check power unit SYMPTOM No video contd 4 pin 12 3 4 No VIDEO INPUT at 1 ACTION Check waveform at pin 13 If correct check TRI and TR2 Check waveforms at pins 15 16 and 17 15 2v L w L PIN16 35V pu ph ms 65n correct check VRZ Issue 1 and Issue 2 boards Change ICI If and VIDEO INPUT correct change modulator Corrupt Paper 1 after ULA change No 3 MHz at ds pin 6 Check socket Check PWR socket 15 not intermittent Check 14 for 45V with no discernible ripple Low amplitude check R25 Check TR3 Check IC pin 32 for 3 MHz Check pin 39 for 14 MHz C
35. heck crystal XI Check pin 13 for 43V Video Incorrect Colour tuning faults Issue 1 and Issue 2 boards SYMPTOM ACTION Dark Screen Check tuning 2 Change modulator Dim Sinclair 097 Check 12V 2 Check C65 for high impedance 3 Check R52 4 Check 5V on 4 pin 3 Wavy lines across 1 Press down on each Screen electrolytic capacitor to see if lines disappear us SO change that Capacitor Check crystal X2 Check change TRI and or TR2 4 Check change W N Self resetting Check Random dynamic Change C54 squares Paper area too low Change ICI Diagonal lines in Change R47 the border area Distorted video 1 Check for 43V at pin 13 2 Change C30 Visually check ICIA circuits or VR2 fails to 1 Monitor ICI4 pin 2 adjust 1 14 pin 13 trimming VR2 waveform 2 Monitor IC14 pin 4 trimming VRI 3 Change 1 14 AREA SYMPTOM ACTION Colour tuning VRI or VR2 d c Change faults cont d shifts ICI4 pin 13 waveform Alternate dark lines Change 4 screen No colour after trimming TC2 ICH pin 17 not Check crystal X2 oscillating 2 Change ICH 3 Change X2 ICH pam 3j 1 Check for broken track 2 Change T fails to tune 3 Change ICH ICH pin 17 output le With oxsclarr logo on correct but still screen ICH pin 2 and no colour boards ICH pin 4 s
36. hould be as at all Issue Nos follows PIN 2 PIN 4 Lf 6575 2 ICH pins 2 and 4 are change modulator Colour faults Pin screen Change crystal X2 Issue 1 Issue 3 boards Blue haze around If untunable Issue 1 and Sinclair issue 2 boards chage ICH ocreen too yellow Change ICH Colour faults cont d Keyboard faults Regulator coil Speaker NOTE Figure 4 2 shows typical waveforms in the speaker circuit Test program SYMPTOM Intermittent colour Red Blue or Green Sinclair logo Washed out colours fault KB2 fault Dead keyboard Wrong keyboard response Keyboard response too fast Coil excessively noise No speaker output Tape Loading Error QLSEorEt ACTION Change TC2 Issue and Issue 2 boards 2 Change 4 Change Check TR2 1 Check for short on 2 or more of the 5 tracks 2 Change membrane 1 Check for short on 2 or more of the 8 tracks 2 Change membrane Change ICI Change Change Change coil 1 Check load input wave forms Check Check D9 4 Reload program Change AREA Test Program cont d Program Loading SYMPTOM Paper area corrupts during tests Border colours are Striped Failure messages Test
37. il hi uk p i tose NNR JL n ERN M ea a END 119 Ci LU I4 EE EE D at a a E 7 EB 1 TT 1 j us Abi u I i a i N M Urna i 4 PEE aT IRE TIPP I rm Tri TE n 93 d 7 n g 1 H RGR ETE 1 CHR 558 W IH m 11 I _ n n TE di n m Hr ats T AI e Hn PE OEN SO dH A A ee ____ _____ 7 _ ______ Tv TIL ______ al Ha tt te tt 4 LLL IM ____ 4 na ____ oxo zum E 1 114 L rn T T ELM
38. ilable to the user for writing BASIC or machine code programs The remainder is used to hold the system variables including 6k bytes reserved for the memory mapped display area In the 48k Spectrum an additional 32k bytes of RAM are provided addresses 8000 FFFF which are implemented using eight 32k bit dynamic RAMs 1 15 1 32 The RAM providing extra memory space for the user is normally fitted during manufacture but may be added retrospectively using the RAM expander kit In addition to the RAMs the kit includes the address multiplexer and read write control ICs IC23 IC26 Board space and the necessary discrete components are already provided on the board Read Write Operations Ihe following description should be read in conjunction with the circuit diagrams given in Figures 1 4 and 1 5 Read Only Memory ICS Ihe CPU addresses the ROM directly during memory read cycles using the address bus A13 AO0 MREQ and RD enable the ROM and the ROM outputs respectively third input CS derived by the ULA ROMCS selects the ROM provided the higher order address bits 14 and 15 are both low These are reserved for accessing the RAM memory which starts with address 4000 1 e address A14 set An external ROM 1C select input supplied via the expansion port on pin 29 selectively disables the on board ROM by pulling the select input high By virtue of R33 placed on the ULA side of the ROM the ULA ROMCS output is effectively inhibi
39. in the column headed ISSUE 2 MODS with references to notes against them These notes are explained below NOTES TO TABLE 5 2 1 The alternative values given for R47 R49 R56 and T63 are used if fitted is 6 001 2 The alternative values for R48 R50 R72 and C65 are introduced to improve the colour quality 3 C74 15 essential on all Issue 2 boards and should be fitted retrospectively At the same time R60 must be replaced with the larger value 4 The introduction of alternative components for R24 and R27 15 essential At the same time C67 replaces 014 and R73 is added 5 Issue 2 boards fitted with the Type 5 112 have either transistor TR6 or diode resistor modification see Issue 2 circuit diagram for details 6 On Issue 3 boards only crystal X2 must have a close tolerance specification 1 e 10 ppm absolute 10 ppm 20 C to 60 C 5 ppm per year 7 On Issue 3B boards the d c converter design has improved reliability R60 is changed from 270n to 681 and C49 is changed from 47nF to 560pF Capacitor C77 1001 has been added 5 1 24 General Capacitor Change Early Issue 2 units were manufactured using a considerable number of 47 nF and 100 nF disc capacitors Where these occur the service engineer should take the opportunity to replace C41 and C49 with axial types TABLE 51 CASE ASSEMBLY DESCRIPTION MANUFACTURER Assembled board as appropriate Table 5 2 Moulde
40. ked at 14 0 MHz from an external source controlled by the logic gate array ULA and has a standard three bus input output arrangement These buses are the Data Bus Address Bus and Control Bus respectively Data Bus 07 010 constitutes an 8 bit bi directional data bus with active high tri state input outputs It is used for data exchanges with the memory and with the ULA Address Bus AI5 AO constitutes a 16 bit address bus with active high tri state outputs The address bus provides the address for memory up to 64k bytes data exchanges and for data exchanges with the ULA It is also used during the interrupt routine see below when scanning the keyboard matrix Control Bus The control bus is a collection of individual signals which generally organise the flow of data on the address and data buses The block diagram only shows five of these signals although others of minor importance are made available at the expansion port see Figures 1 4 and 1 5 for details Starting with memory reguest this signal is active low indicating when the address bus holds a valid address for a memory read or memory write operation Input Output reguest is also active low but indicates when the lower half of the address bus holds a valid I O address for the ULA during I O read write operations The read and write signals RD and WR are active low and one or other is active indicating that the CPU wants to read or write data to
41. loose there overtightened screws Look for dry joints cracks in print or cracked boards badly fitted components especially ICs dirty or tarnished contacts pins holders edge connectors damaged keyboard tails and fins are certainly not uncommon for whatever reason Before investigating any fault check any add ons and interfaces to the computer for broken solder etc caused by user wiggling them about It is also essential to note if add on is loose or faulty which will give a guide to any damage so caused This will also determine if fault in add on not computer Knowing what add ons are used can be a good guide to probable fault for example suspect TR4 blown and or destroyed RAMS if a Kempton is used Check if customer has been inserting or removing any add ons without first switching off and point out how this practice has damaged machine and costing him unnecessary expenditure If this 15 admitted then check TR4 first then RAMS and see symptom 3 2 WONT LOAD FROM RECORDER Almost invariably this will be caused by the alignment of the recorder head not being good enough The recorder will play music etc and function well but it will still need adjusted to operate the Spectrum properly and it matters not whether it is an old or just newly bought recorder Disconnect Spectrum from recorder and with any tape playing use a long thin bladed screwdriver to adjust the azimuth screw through the hole normally provided for this purpo
42. n of each row and column bridged by a normally open switch contact The row outputs and column inputs are shown connected by separate ribbon cables and KB2 one to ULA and the other to the high order address lines 15 8 Pull up resistors R64 through R68 ensure that when the address bus is in the high Z state or none of the key switches is closed row outputs KBO to KB4 remain high 571 ROWS ADORESS BUS COLUMNS FIG 1 3 KEYBOARD MATRIX INTERCONNECTIONS 1 See ETT ph DATA 805 5 3 3 5 4 5 4 1 5 4 2 5 4 3 When the keyboard scanning routines are entered performs successive I O read cycles setting the IOREQ and RD lines to the low the same time the I O port addresses placed on the upper half of the address bus are modified with each cycle such that each of the address lines A15 through 8 is set low in turn the other lines remaininghigh The seguence starts with I O port address FE driving address line 8 low The keyboard matrix also sees this potential on column 6 applied via D6 and the ribbon cable KB2 Thus when any of the switches the inter section with column 6 15 pressed the corresponding row output supplying the ULA via the second ribbon cable is pulled low The row signal s is subseguently inverted by the ULA and placed on one of the five low order data bus lines For example if the CAPS SH
43. n pin 3 and the colour difference signals on pins 2 and 3 respectively is nominally OV d c In the Issue 3 Spectrum two active networks incorporating IRS and TR9 eliminate the potentiometers greatly improving colour stability The level shifted colour difference signals input to ICIA are then encoded by guadrature modulating two 4 43 MHz chroma sub carriers The sub carriers are generated with the assistance of an external crystal X2 and a CR lead lag network introducing a 90 phase shift between pins 1 and 18 A further difference between the Issue 2 and 3 Spectrums lies in the bias oscillator The early issues incorporate a trimmer TC2 allowing chroma sub carrier freguency to adjusted on the later issues the freguency is fixed The resultant modulated colour difference signals are finally mixed producing a composite chroma sub carrier at ICIA pin 13 At this point the chroma signal is a c coupled to the base of TR2 and added to the inverted luminence signal on TRI collector The resultant composite video is then buffered and applied to encapsulated UHF modulator operating on European standard channel 30 Keyboard Scanning Every 20 ms i e once per maskable interrupt the CPU systematically scans the keyboard recording which keys if any have been pressed The scanning method is described below with the aid of Figure 13 As the figure clearly illustrates the keyboard consists of an 8 x 5 matrix the inter sectio
44. nimise rather than remove this effect Proceed as follows a Set up the Spectrum to display qreen PAPER with red INK b Type in three or four lines of characters and monitor the screen c Adjust trimmer TCI to minimise the effects of distortion 3 2 25 2 1 242 SYSTEM TEST The system test for the Spectrum may be undertaken using the ZXTP taped program see 1 1 Test Equipment in Section 4 loaded conventionally this requires that the keyboard 15 connected The test should be carried out with the Spectrum connected to its own power supply The test program exercises all of the Spectrum circuitry with the exception of the SAVE function t st this function Small possibly one line program should be typed in SAVED and then VERIFIED as described in the instruction manual 252 SECTION 4 FAULT DIAGNOSIS AND REPAIR Sub Section LIST OF CONTENTS Page No 1 Introduction 4 2 Test Equipment 4 2 Modification History 4 3 Modifications Issue 1 Board 4 4 Modifications Issue 2 Board 259 32k Extension Memory 16k 48k 4 5 Hitachi vs NEC 4 6 2 Fault Diagnosis 4 6 Techniques 4 6 Power Supply Unit 4 7 Initialisation 4 7 Memory Check 4 8 Keyboard Structure 4 10 Fault Finding Guide 4 11 3 Repair 4 19 4 lok to 48k Upgrade 4 19 Integrated Circuits Link Settings 4 19 Issue 2 Board 4 20 Issue 3 Board 4 20 bgl INTRODUCTION Test Equipment Section 4 15 intended as a guide to fault diagnosis
45. ocedure Key in the instruction PRINT PEEK 23732 PEEK 23733 256 The value printed should be 4 8 a for a 48k unit 65535 b for a 16k unit 32767 The value printed in each instance is the last valid memory location and in a serviceable unit would be as set out above Therefore if a different value n is printed the faulty location will be n 1 If the value returned is less than 32767 the fault lies in the original 16 of RAM The following example illustrates the method of relating a faulty location to a faulty IC Example If a 48k Spectrum is giving a memory of 25 25k key in the following instruction PRINT PEEK 23732 PEEK 23733 250 Assume the answer displayed is 43200 therefore the faulty location is 43201 stops at last valid location 1 POKE 43201 85 PRINT PEEK 43201 answer If answer is 85 key in POKE 43201170 PRINT PEEK 43201 answer If answer B is anything other than 170 look up in the following table which to change e g if answer is 234 change IC21 Similarly if answer A is other than 85 refer to the table to find the faulty 1C Data 85 Data 170 Size of Error Faulty RAM location if IC6 IC13 IC15 IC22 Error Bit lt 32767 gt 32767 84 171 1 0 IC6 5 87 168 2 1 IC7 16 81 174 4 2 IC8 1 17 93 162 8 3 IC9 IC18 69 186 16 4 0 1 19 117 138 32 5 1820 21 234 64 6 1 12 IC21 213 42 128 7 IC13 IC22 If there is more than one faulty
46. onfined to checking that the internally generated power supply voltages and two oscillator frequencies are correct Adjustment instructions apply strictly to the Issue 2 Spectrum boards only but generally relevant to the Issue 1 Spectrum as well To carry out the setting up procedure it is first necessary to remove the ZX SPECTRUM from the case Section 2 Assembly Disassembly For convenience the keyboard may also be disconnected 152 Voltage Check Check that internally generated power voltages are as follows Circuit Reference Nominal Value Tolerance IC6 pin 9 0 25V IC6 pin 1 5V 5 5V to 4V IC6 pin 8 12 1 2V LT side of C52 12VA 1 2V 13 Colour Adjustment Potentiometers and are used to effectively null the voltages between pins 4 and 2 for and pins 2 and 3 for on 4 1 1889 To allow for thermal drift the potentiometers are set for non zero voltages furthermore these voltage off sets are set to satisfactory but non optimum levels in production and optimum values may be used to advantage in servicing The relevant figures are given in the following table voltages are given relative to pin 3 of LM1889 3 1 4 1 5 Pot IC14 Factory Setting Optimum mV Overall Range Pin No mV Voltage Tolerance mV VRI 4 130 20 50 5 45 to 150 VR2 2 75 20 50 50 45 to 100 5 Sub Carrier Oscillator The chrominance sub carrier oscillator frequency sho
47. ons replace all ceramic capacitors by axial ones and replace C46 by a high temperature luf type All resistors to be changed to show the second value show in centre pages circuit diagram herein same applies to capacitors Weak sound Only if particularly noticeable should the sound section be changed to same as shown herein Tape and Sound Circuits 5Vp p at ear socket for 2Vp p at verifies ICI Alignment Only needed for early models Place meter on pin 4 of IC4 and adjust to obtain 130mV adjust VR2 to obtain 75raV at pin 2 with a 20mV allowable error either way Use TC2 to set colour subcarrier frequency to 4 433619MHz to 50Hz either way TCI only helpful to improve screen colour pattern Alignment models Run the programme to display the eight colours in sequence from black to white This is normally given as 10 FOR A 0 TO 7 20 FOR B 0 TO 3 30 PAPER A PRINT 40 50 NEXT 60 GOTO 10 If this shows incorrect or missing colours then align as stated for early models See repair data for later models REPAIR DATA 1 GENERAL REPAIR PROCEDURE AND NOTES ON ALL FAULTS These computers are reportedly very unreliable with some 50 of new ones alleged to have to be returned for replacement Many faults are due to loose or badly fitted components so that a good checkover is essential for this reason to determine if a factory failure first Check heatsink first for any reported fault is it
48. out in order of priority will however isolate the major fault area FUNCTION CIRCUIT REF WAVEFORM VOLTAGE Voltage regulator ve side of C50 9V d c 2 0V At less input than 7V the regulator not operate correctly Voltage regulator ve side of C34 5V d c 0 25 output discernable ripple On board power supply outputs 15V d c IC6 pin 9 5V d c 0 25V discernable ripple 5V d c IC6 pin 1 5V d c 12V d c IV6 pin 8 12V d c 12VA to IC14 only LT end of C52 12V d c Clock pulses IC1 pin 32 14MHz squarewave at base and amplitude collector IC2 pin 6 Address and data side of R17 R23 Waveform of amplitude 3 5V lines following through to relevant RT side of R1 R8 ICs If these tests prove satisfactory check pin 14 C2 pin 11 and 105 28 for 45V Also check for ground at pin 40 IC2 pin 29 and IC5 pin 14 If all is still satisfactory at this point and ICI 15 the plug in type replace ICI If replacement of ICI does not cure the fault check the address and data lines of IC2 and 5 for active data It is possible that one of or RAM control lines has become faulty therefore comparing with known serviceable board if possible check the waveforms at the following points at origin and destination a 2 Pin 16 INT Pin 17 NMI Pin 20 IDREQ Pin 24 WAIT Pin 19 MREQ Pin 23 HICTEQ Pin 21 M Pin b KtbM Pin 22 WR
49. roduced to the top edge of the template Previously only the other 3 edges had tape This modification should be introduced whenever template lifting 15 found to be a problem d See Items 1 3 g and h above 15 Modifications Issue 3B Board Although functionally similar to the Issue 3 board the layout differs The DC converter design has been improved providing greater power supply reliability Component changes are as follows see Fig 1 5 for details C77 IQOnF added C49 changed from 47nF to 560 R60 changed from 2701 to 68n TR4 can be either ZTX650 or TIPP31 32k Extension Memory 16k to 48k Board Issue 1 The extension memory is supplied as a plug in module which is inserted into sockets near the edge connector The ICs used are either TI 4532 3 or TI 4532 4 and all ICs in a unit must be of the same type i e all must be 3 or all must be 4 Board Issue 2 The extra memory is obtained by plugging in 4 logic ICs and 8 memory ICs see Sub Section 4 The ICs used are either TI 4532 3 or TI 4532 4 and all ICs must again be of the same type It should be noted that the RAM select signal is OV for the 3 and 5V for the 4 A link on the board provides the required select level 4 5 1 7 2 1 Board Issue 3 This allows OKI ICs to be used in place of TI 4532 Again all ICs must be of the same designation Appropriate links 2 must be fitted in the grid located on the board between the edge conne
50. se The object is to obtain sharpest possible sounding note noting that if note is in the least muffled sounding then there is no chance of the Spectrum loading from it If no hole is provided this should be done with the recorder cover removed Although it is reccomnended that volume should be set at midpoint it is far better to vary volume setting to that at which maximum treble 15 obtained Finally give head a good clean and recheck setting If the adjustment does not cure the problem then save a short programme from the computer or use one previously saved and if this doesn t load then it 18 safe to assume that there is fault probably in the computer In this case check connections to computer and the circuit from the edge connector to the first I C 0 gn C t L 3 ON mmo gt ae nr OO Po Ee 5 Later types board Sinclair Spectrum fiv ae ae amp fe23 1552 5 D Ac 4 tiu alo F c3 EH m dade T S IE LEEN gau pili 1 Ld 4 L ot E M p bet 176 760 MP 476 tome models X ff auf ale
51. ssembly is carried out using the reverse procedure to that of disassembly not overtighten self tapping fixing screws When replacing a keyboard component note that the membrane keys into projections on the case Place the keypad over the membrane and ensure that it is positioned and seated properly Faulty installation can result in depressed keys being trapped under the template during subsequent key operations To install the template place double sided adhesive tape around all four edges locate it in position on the case and apply firm pressure around the edges 12 mm tape on sides and bottom 6 mm at top 2 1 2 3 When aligning top half of case with the bottom half ensure that the two keyboard ribbon cables are not trapped between projecting components within the case In their correct positions there is sufficient room for the cables to take up a comfortably curved position inside the case If a cable is trapped and bent double an open circuit will sooner or later result SEC LION 3 SETTING UP AND SYSTEM TEST Sub Section LIST OF CONTENTS Page No 1 General Alignment al Introduction osl Voltage Check Spl Colour Adjustment uu 12201 22 14MHz Oscillator 322 2 System Test 3 9 l GENERAL ALIGNMENT 1 1 Introduction The Issue 3 Spectrum modification removes need for adjustment of the colour tuning using potentiometers and trimmers Therefore the setting up procedure for this board is c
52. te Li TIE A LT Umm ML CIEN XUI ke en MI DUE EXER QE a 2 1 i a un in NER 1 150 ks 1 as ee E n aia ten sU Hcr S 1 all ah ae tU m APPROVE This technical manual was OCR ed for the Sinclair world by Andy Dansby andydansby yahoo com All 3ntellicral information contained inside this technical manual is the property or Amstrad Thank you Clive for the ZX Spectrum SERVICINGMANUAL FOR ZX SPECTRUM LIST OF CONTENTS INTRODUCTION SECTION SYSTEM DESCRIPTION SECTION 2 DISASSEMBLY ASSEMBLY SECTION 3 SETTING UP AND SYSTEM TEST SECTION 4 FAULT DIAGNOSIS AND REPAIR SECTION 5 PARTS LISTS LIST OF ILLUSTRATIONS Fig No ZX Spectrum Block Diagram 1 1 Expansion RAS CAS Timing Read Cycle shown 1 2 Keyboard Matrix Interconnections 13 ZX Spectrum Issue 2 Circuit Diagram 1 4 ZX Spectrum Issue 3 Circuit Diagram 1 5 Keyboard Format 4 1 Speaker Load Input Waveforms 4 2 Expansion Memory 1C Locations 4 3 Issue 3 Links vs IC Manufacturer and Type 4 4 Printed Circuit Board Issue 2 Component Layout 5 1 Printed Circuit Board Issue 3 Component Layout Printed Circuit Board Issue 3B Component Layout 5 3 Prepared by THORN EMI DATATECH LTD
53. ted Interface 1 uses this 1 4 a lap uir TENE LN a _ T rr i Cod wj t Ld Tab L pla I fil 1 pa Clk EERE EEE RES IN ill qe oe il eis iae Miel dl a Aum IRE SALES OF THESE RUIT k M M n M ie n emi P I un MCN nin Y a EET m alil sm eo IM m SSS SS TL 1 8 He HHE TIL nn mr pee DL S ty ff BREL 1 d L 44 inn mr ww 1 aur cA TUE TES dn TII TI TH Sieg
54. that connecting items such as standard capacitors may not be shown Edge Connector 28 pin double sided to which no interface may inserted or removed whilst computer is switched on Plugs amp Cables use only genuine Sinclair issue or HK plugs etc Power Supply Where any possibility of fluctuating mains exists a transient suppressor should be fitted Links TI T3 for Texas THS4532 3 4 for Texas TMS4532 4 for OKI HSH3732H for OKI MSM3732 L Other Service Hepair Manuals 5 Rank A823 CTV Chassis Philips G8 CTV Chassis Thorn 3000 3500 CTV Chassis Thorn 8000 8004 8500 8600 CTV Chassis Rank T20 20A CTV Chassis The Tunbridge amp McCourt T V Repair Manuals The Tunbridge Video Repair Manuals SERVICE DATA Modification of earplug Connect a 330 ohm resistor between signal and earth leads of earplug to allow earplug to be left in place while saving a programme Inserting or removing such items joysticks especially via a Kempston interface while the computer is switched on will damage the power resistors and regulator Modification to voltage generator circuit Where not fitted already insert a 22uf capacitor between TR4 and D15 as shown in the circuit diagram this will ensure the correct 12v supply On early models replace R60 by a 270 ohm resistor and fit C74 if missing Ensure that the 12v supply is 12 Manufacturer s advised modifications In early versi
55. the row address is latched RAS goes low selecting the high order address bits 13 7 giving the column address The RAS CAS outputs from the ULA are generated in seguence in response to MREQ and Al4 from_the CPU The DRAMWE output also from the ULA 1s a decode of the RD WR waveforms telling the RAM tto expect either a read or a write cycle It is also apparent from the circuit diagram that the ULA access RAM by generating a set of addresses independent of those generated by the CPU The address port for the RAM is therefore dualled by the insertion of small value resistors RI7T R23 on address multiplexer side of the RAM This ensures that where there is likely to be conflict between the ULA and CPU the ULA address has priority Priority is assigned on the basis that the ULA must access the memory mapped display area in the RAM at set intervals in order to build up the video for the TV display If the ULA is about to access the RAM and it detects either 14 or 15 the CPU 15 also about to access the RAM the ULA inhibits the CPU clock temporarily halting the CPU memory transaction until its own transaction is completed Resistors to R8 in series with the data bus lines perform a similar function to the address portplr sistors described above They ensure that the ULA does not see CPU write data while the ULA is accessing the RAM Refresh for the standard 16k dynamic RAM is accomplished during normal read
56. uld be 4 433619 MHz 50 Hz This frequency may be checked adjusted by usinq one of two methods listed in a or b below Apply power to the power socket using a bench power supply set at 9V Current consumption will be approximately 500 mA to 700 mA for the 16k Spectrum and 700 mA to 900 mA for the 48k Spectrum a Feed the Spectrum modulator output via a co axial cable into a standard colour TV receiver Measure the frequency of the locked TV chroma sub carrier b Connect pin 17 of IC14 1 1889 via a 4 7 pF capacitor and a lead to the frequency meter is recommended that this 18 done using a jiq made up from an 1C test clip Pin 18 of this clip must be removed to minimise stray capacitance Connect a 10k ohm resistor between the input terminals of the frequency meter Measure the frequency and adjust trimmer TC2 if the measured frequency is outside tolerance 14 MHz Oscillator This frequency is not readily set by working to a specified frequency and tolerance Issue 2 boards trimmer should be adjusted to minimise the effects of beat frequencies which cause waves of distortion to flow across the screen These are particularly apparent with certain colour combinations e g red INK or green PAPER and the phenomenon is sometimes referred to as dot crawl It is stressed that adjustment of this frequency is not straight forward as deviations due to temperature change are easily visible tuning should be adjusted to mi
57. y a high temperature component This modification is required for efficient operation of certain machine code software and should be implemented on all units It has been implemented in manufacture for all ULAs 5 12 2 and later D14 replaced by C67 100 pF R24 changed from 3k3 to Ik R27 changed from 680 n to 470 n R73 added between 14 32 and 5 A significant cause of problems has been found to be failure of the internal power supply transistor TRA The circuit may be improved by changing the value of R60 from 100 to 270 and connecting a 4 7 uF electrolytic perferably radial type with positive end to TR5 emitter positive end of C34 and negative end to TR5 base to R58 4 4 14 Modifications Issue 2 Board A number of modifications have also been introduced for the Issue 2 board These should be checked and if necessary introduced retrospectively a These components should be changed if colour quality needs upgrading R48 changed from 4k7 to 2k2 R49 changed from 18 to 8k2 R50 changed from 8k2 to 4k7 R72 changed from 47 k or 18 k to 10 k C65 changed from 100 yF to 22 yF b Early Issue 2 boards were manufactured using a considerable number of 47 yF and 100 uF disc capacitors C41 47 nF and C43 100 nF should be replaced with axial components to prevent undue risk of short circuits c To prevent lifting of the keyboard template a thin strip 6 mm wide of double sided tape was int
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