This technical manual was OCR`ed for the Sinclair world by Andy
Contents
1. m SERVICE MANUAL ZX Microdrive ZX Interface 1 ZX Interface 2 APPROVED This technical manual was OCR ed for the Sinclair world by Andy Dansby andydansby yahoo com All intellicial information contained inside this technical manual is the property of Amstrad Thank you Clive for the ZX Spectrum SERVICINGMANUAL FOR ZX MICRODRIVE INTERFACE AND INTERFACE 2 LIST OF CONTENTS SECTION 1 SYSTEM DESCRIPTION SECTION 2 DISASSEMBLY ASSEMBLY SECTION 3 SETTING UP AND SYSTEM TEST SECTION 4 FAULT DIAGNOSIS AND REPAIR SECTION 5 PARTS LIST LIST OF ILLUSTRATIONS Fig No ZX Interface 1 Block Diagram 1 1 Circuit Diagram 1 2 ZX Microdrive Circuit Diagram 1 3 ZX Interface 2 Circuit Diagram 1 4 ZX Microdrive Head Chassis Mechanical Layout 4 1 ZX Interface 1 PCBLayout 5 1 ZX Microdrive Base Board Layout 302 Head Board Layout 3 3 Prepared by THORN EMI DATATECH LTD _ for SINCLAIR RESEARCH LTD OCTOBER 1985 Sinclair Research Ltd SECTION 1 SYSTEM DESCRIPTION Sub Section LIST OF CONTENTS Page No 1 ZX Interface 1 1 1 2 ZX Microdrive 1 5 3 ZX Interface 2 1 8 4 Power Supply 1 9 l ZX INTERFACE 1 The ZX interface 1 combines the three functions of microdrive controller local area network and RS232 interface Using it the Spectrum can control up to 8 microdrives can connect up to 64 other Spectrums to form a network and can communicate with other computers and peripheral device2. t tao INPUT tt4 b 150 IF 25 THEN PAPER 0 INK 7 CLS PRINT WRITE FAILURE CLOSE 4 155 PRINT H INK 4 ERASE TEST LIC ERASE lle di Te t 175 CLS 1 20 PAPER INK 7 CLS PRINT DEI VE 3 PAUSE STOP 3 2 3 3 4 1 With a blank cartridge inserted in the Microdrive the above program performs a simple exercise of the writel read erasel functions An indication of another class of problem can be gained from the screen during the format operation If the screen remains white during the third stage of the format this is a sign of noise on the write line In this case the motor alignment the Microdrive ULA or the voltage regulator should be checked waveforms at either end of and C2 are significant for fault diagnosis Key in OUT 239 252 OUT 239 254 ENTER to set the ZX Microdrive spinning Look at the waveform ensuring that the oscilloscope lead is earthed on the body of the regulator There should be packets of oscillating voltage one long two short separated by quiet areas The oscillating voltage should be about 0 5V peak to peak but the important thing is that it should be consistent and not vary The other important parameter is the noise level in the quiet patches This should not be more than 25mV The best way to check waveforms is to compare with those on a known good unit ZX INTERFACE 2 The most practical test for the ZX interface 2
3. 27 THEM TO PRINT PA 1 553 SUB 200 IF NOT 4 THEN TQ 33 SO SUR 200 TH GO 33 PRINT PRINT cet GO TO FAIL STOP TEST OUT oc ute Ir 2871 LET 247 INT 4 2 THEN GO TO OUT 247 0 LET PRINT IN 247 IF INT d j 3 7 THEN GO TG be STOF FOR TO 4 STEP 1 IF d 2 i THEM LET degs MEZ i LET 7 RETURN d The first part of the 85232 test checks the data send receive and the second part checks the DTK function H the RS232 function still does not work despite passing these two tests the ULA must be functioning and the voltage levels between the ULA and the RS232 socket should be checked Clock Test Try formatting a cartridge in the ZX Microdrive If the screen border remains black during the first part of the format this indicates a clock problem in the Interface 1 and the crystal circuit should be examined ZX MICRODRIVE There are some basic tests that can be carried out using the following um This should be run with the microdrive unit connected to a nown good system 6 LET 3 1 7 PAPER 7 CLS BPOSDEF INK Z PRINT 5 2 Micredrive Interfacel tester 100 LET 8 FOR 1 TO 8 LET a a ta NEXT 1 10 FRIMT 0 INK WRITE TEST 105 OPEN m 2 Text 11 PRINT 4 2 120 CLOSE 4 125 PRINT amp INK 5 READ TEST 1 0 OPEN 40
4. 512090 2 Kenure 512095 Spectrum Logo James Cook 512095 Red G Engl ish LN28PP T 5 way x 1 in flex cable Dean 5 way x 1 1 2 in flex cable Dean 7 way daisy chain Pye 512102 Pan hd 4 2 mm x 1 4 in Ig Plastite Pan hd 4 2 mm x 1 2 in Ig Plastite C sk 4 2 mm x 3 8 in Ig Plastite TABLE 57 7 INTERFACE 2 Description Manufacturer Type Integrated Circuit MCE HT62001 28 way edge connector Pye 15 way edge connector Pye 9 D type connector ITT Cannon Canton Hill SRC126 Canton Hill SRC127 Canton Hill SRC128 C sk 2 9 mm x 13 mm Ig Plastite RA dm 1710 0 RABAR _ IN m aes uns fs 1000900 00 QOWOWDUN 25 oO D TH PD p 1 252758 c FIGURE 5 1 2 INTERFACE 1 BOARD LAYOUT 5 7 5 1 SS3R DE FIGURE 5 2 ZX MICRODRIVE BASE BOARD LAYOUT T aa 4882 1563 FIGURE 53 7 MICRODRIVE HEAD BOARD LAYOUT 5 8
5. M headsprings check cartrid9e for scratches n Weak clamp Spring listen for clicks crunch sounds 111 Correct the operation of the ratchet spring assembly NOTE If motor has over heated check for buckled base plate Renew complete microdrive BILE Renew complete microdrive unit Renew LED LED is push fitted 3 5 ZX Interface 2 3 5 Since the ZX interface 2 comprises one integrated circuit and a number of connectors fault finding is simple Connect the unit to a Spectrum and connect a games ROM cartridge two joysticks and a printer to the unit Initiate the game and check out all functions If a fault 1 found power down and replace Printer faults must be due to discontinuity between input and output since pin to pin connections are used 4 REPAIR 4 1 Renewal of components should be carried out using recognised desoldering heatsinking techniques to prevent damage to the component or the printed circuit board General points to note are The head assembly in the microdrive is the only component which MUST NOT be changed o When replacing the plug in 1 in interface 2 use the correct removal and insertion tools When handling ICs take normal anti static precautions It vis recommended that only a suitably earthed low power soldering iron be used When removing a soldered in 1C cut each pin and remove the component before individually unsoldering each pin After a
6. 1 3 4 1 i b J g m t T Do un n 12 3 i 1 i L 1 1 n 5 H 1 t 3 5 t TrsscC lt is 1 W 5E 11 5 05760 1 nj TT i t1 15768 Y IL Hn uir c2 E4835 701 yo LILA f j SB CONNECTOR 7 MICA OME 1 OF LE TERN r Et r5 111 W A A 58 Ka k B TA TW EAIMECTHA 2 Ha I rra vipt ult n The euet toumegtens a3 Al T T a n ats INTERFACE 1 FIG 1 2 CIRCUIT DIAGRAM DSK 12860 ISSUE 58 5 16 Zh 68 7 13 5 Rh A Rh 83 n t 2 43 800 Ch 0 01 L x m uwa G ar w m r 0 BOARD riy 12100 n R7 150 180R T 1 2 64 t 5 itn apo ERASE CIMMS fll COMMS CLE 1 2 i mus YY at R B AF TET Hl RI R ERASE ci COMMS OUT L8 COMMS ELK 78 PY 1 14 DATA 2 18 gy LA WA PROT 7A 7 8 s Gs fA 6 gp dj 7 5 031 85 814 Les M SW BASE BOARD
7. 5 Carbon CAPACITORS 220 2 5 Ceramic Axial C2 220 pF 2 5 Ceramic Axial 0 47 50 V Electrolytic Axial C4 0 22uF 50 Electrolytic Axial 330 pF 2 5 Ceramic Axial C7 NOT USED C8 No 2 5 Ceramic Axial C9 NOT USED CIO 48nF 80 20 50V Tayo Axial DIODES DI 14148 Signal D2 IN4148 Signal TABLE 5 4 ZX MICRODRIVE BASE BOARD ASSEMBLY Circuit Value Rating Manufacturer Notes Reference Tolerance Type RESISIORS RI 33KO 0 25W 5 Carbon R2 IKO 0 25W 5 Carbon R3 820 Q 25W 554 Carbon RIO Link CAPACITORS 25 47 480 20 50V 1 1 OF 22UF Electrolytic Axial DIODES D3 IN4148 Signal D4 IN4148 Signal TRANSISTORS QI Motorola 184 BC184B BCI84C Q2 Ferranti ZTX551 Ferranti BCIMP permitted exceptionally TABLE 5 5 7 MICRODRIVE HEAD CHASSIS ASSEMBLY Item Description Manufacturer Type Head Assembly This component must not be changed Motor 9V 2400 rpm Mabuchi EG 500AD 9F clockwiserotation Drive Roller Smooth wall RE components Plastic Roller Microswitch Burgess Screw 2 off C sk 4 mm Posidrive M2 5 Screw 1 off Pan hd 2 28 mm x Plastite 3 8 1g TABLE Item Cover LED Inner Flex Outer Flex Connector Screw 4 off Screw 1 off Screw 2 off Item SKI SK2 SK3 SK4 Upper case Lower case Case lid Screw 4 off 5 6 ZX MICRODRIVE CASE ASSEMBLY Description Manufacturer Type 5
8. p c board to the base and a further cross head screw accessible on the underside of the microdrive securing the base to the head chassis CAUTION Having removed the base take care not to place excess strain on the flex cables linking the head and base p c boards Do not attempt to separate the head p c boards from the head chassis as the read write head alignment Is critical Special tools are needed to re align this assembly Assembly is the reverse of disassembly taking care not to trap the flying leads between the head p c board and the base After replacing the top cover fit a new adhesive trim ZX INTERFACE 2 Turn the interface upside down and remove 4 cross head screws After lifting the base clear the p c board is easily separated the top Assembly is the reverse of disassembly taking care to orientate the p c board correctly SECTION 3 SYSTEM TEST Sub Section LIST OF CONTENTS Page No 1 1 1 2 2 1 Q Ne Introduction ZX Interface 1 ZX Microdrive ZX Interface 2 WW 024 Q N INTRODUCTION The use of the following test procedures is strongly recommended after carrying out unit repairs thus ensuring that a once defective unit is completely operational before return to the owner The procedures may also be used effectively during fault diagnosis Section 4 In each instance where the list of test equipment specifies a ZX Spectrum or ZX Interface 1 or a ZX Microdriv
9. 12181 MSIOR MEIN 4 SWITCH 58 2 COMMS DUT t __ _ _ _ CMMMS 28 nr i FIN 3 FIN 3 RENE Ug sa Pl _ 1 3Y LA B 15 SOLOER SIDE WA FEM 7 ITT 68 7A 78 MICRODRIVE FIG 1 3 CIRCUIT DIAGRAM CSK 10626 Lm __1 _____ 77 4l Em 58548 a susugnus i 23 T iF RJ mp opos B T xs TEM CC T tHe 3 5 E Bi mr E zn LLL _ 5 b 11 I re teen ea ib mE cm T n 11 9 iia I g LLL LL mi T SEE H Sak 452 s 33 22 eee z wui s SUE SECTION 2 DISASSEMBLY ASSEMBLY Sub Section LIST OF CONTENTS Page No 1 Introduction 2 1 2 ZX Interface 1 2 1 3 ZX Microdrive 21 4 ZX Interface 2 22 1 INTRODUCTION i 244 feed 3 1 This section details the disassembly procedures for the two interfaces and the microdrive In general the assembly procedure is the reverse of disassembly although certain precautions are included where considered necessary The only tool reguired is a small cross head screwdriver CAUTION This eguipment contains CMOS integrated circuits All surfaces a
10. damage Suspect units should be connected into the test system using workshop cables and connectors which are known to be serviceable If a successful test result is obtained then the customer s cable connector must be faulty Initial Checks Before power is applied to a suspect unit a check should be made between each power rail and OV to isolate any short circuits Check for open circuit between and the pins set out in the following table 4 4 PIN OV PIN DEVICE CONNECTOR NO Ground POWER RAIL ZX Interface 1 5 4 3b 6b 5 4 9 V 20 6b 5 22 6b 412 V ZX Microdrive Edge conn 4b 6b 9 V ZX Interface 2 Spectrum 3b 6b 5 edge conn 4b 6b 9 V 3 3 ZX Interface 1 3 3 1 With this unit connected to a known serviceable system apply power Carry out the checks set out in the table below to establish start conditions CAUTION Do not connect interface 1 with the power ON as damage to inductance LI and the ULA may occur FUNCTION CIRCUIT REE WAVEFORM VOLTAGE VALUE On board d c power supplies 5 pin 40 5V d c 0 25 no discernable ripple 5 Pin 20a of 5 V d c exp conn 112 V 811 PL deg 12271 R17 gt y MESE ToS R34 Clock pulses Id pin 5 8 0 MHz squarewave at t5 V amplitude 3 3 2 Carry out the ZX Interface 1 tests described in Section 3 2 which also gives details of fault diagnosis As an additional check try loading program from Microdrive The fol
11. is a functional check using a suitable ROM cartridge e g Space Raiders and a pair of industry standard joysticks 3 3 EA 4 2 4 3 ZX Interface 2 is plugged into the ZX Spectrum and the ROM cartridge software RUN in the normal way Provided the game employs joystick controls it is simple matter to determine whether the game 15 running correctly and the UP DOWN LEFT RIGHT and FIRE control switches are operational If the game does not run suspect the ZX interface 2 p c board and or edge connectors The same applies if the joysticks are non operational but also include a check of the 9 pin D type connectors and possible renewal of the ULA SECTION 4 FAULT DIAGNOSIS AND REPAIR Sub Section LIST OF CONTENTS Page Mo 1 Introduction 4 2 Modification History 4 2 3 Fault Diagnosis 4 4 Techniques 4 4 Initial Checks 4 4 ZX Interface 1 4 5 ZX Microdrive 4 6 ZX Interface 2 4 8 4 Repair 4 8 INTRODUCTION 1 1 Section 4 is intended as guide to the fault diagnosis and repair of the ZX interface 1 ZX microdrive and ZX interface 2 is assumed that the service engineer has a reasonable knowledge of electronic theory servicing and fault finding techniques and has access to the test equipment and tools required to carry out the task The following items of test equipment and materials is the minimum recommended a Oscilloscope with rise time 0 02 S cm b Oscilloscope probe 10 c Multimeter ge
12. 6 1 6 1 1 6 2 1 7 1 7 1 Network The NET jack sockets SK2 and SK3 are connected in parallel to the NET input pin 36 on network is common emitter in that all stations on the network can either source current into the net or be turned off Jack plugs are used in such a way that any socket not used automatically terminates the network When a jack is inserted in the socket it breaks the connection to a 330n resistor R22 and R23 disconnecting it from the circuit With a network set up the two end stations would be the only ones with the 3301 resistors circuit There is therefore their combined resistance giving a pull down impedance of about 165n to the circuit Zener diode Zl provides protection for NETIN by clamping pin 16 to 5 1V Microdrive Control Seven lines are used by gate array to control the input and output of data to and from the microdrive These signals are summarised in the table below SIGNAL FUNCTION 1 PIN NO ERASE Control of erase current to microdrive 35 R W Instructs microdrive to either read or write 29 COMMS OUT Microdrive selection Also selects NET RS232 when microdrive not in use 30 COMMS CLK Microdrive clock 31 WRPROT Input which informs of the status of the write protect microswitch on the selected microdrive 32 DATA 1 Data from to microdrive track number 1 37 DATA 2 Data from to microdrive track number 2 38 1 7 2 implementation of the above
13. PCB ASSEMBLY contd Circuit Value Rating Manufacturer Notes Reference Tolerance Type RESISTORS contd R26 10KO 0 25W 5 Carbon R27 NOT USED R28 6K8 0 25W 5 R29 6K8 0 25W 5 R30 270R 0 250 5 R31 IKO 0 25W 5 Carbon R32 680R 0 05W 5 R33 10 0 25W 5 R34 330R 0 25W 5 R35 47KO 0 25W 5 R36 10KO 0 25W 5 TRANSISTORS QI BC213C Q2 BC213C Q3 Motorola BC184 BC184B or BC184C Q4 BC213C Q5 BC213C Q6 Motorola BCI84 BCI84B or BCI84C Q7 NOT USED Q8 NOT USED Q9 Motorola 184 184 or 184 010 Ferranti ZTX313 Alternative Ferranti ZTX313 15 BCIS3L NOTE fitted on later boards only Ferranti 184 permitted exceptionally MISCELLANEOUS SKI ITT Common Pye 9 way D socket SK2 Tuda 3 5mm jack socket XI 8 OMHz 1 nominal G English HC18U 5 3 INTEGRATED CIRCUITS TABLE 5 2 2X INTERFACE 1 CASE ASSEMBLY ICI ULA IC2 5V Ferranti ULA2G007 78 05 Regulator Item Description Manufacturer Type Cover Kenure 512110 Base E Kenure 512111 Screw 2 off C s LO ammo Plastite Screw 2 off C sk 4 2 mm x 3 8 in Ig Plastite Screw 5 off C sk 4 2 mm x 1 2 in Ig Plastite Ribbon Cable Interface 1 to Microdrive Varelco Jack Cable 3 5 mm jack ends x 2 m Ig Able TABLE 5 3 7X MICRODRIVE HEAD BOARD ASSEMBLY Circuit Value Rating Manufacturer Notes Reference Tolerance Type RESISTORS R4 150 0 25 5 Carbon R5 180 0 25 5 Carbon R6 to R9 4K7 0 25W
14. connector 01 52 from for example Interface 2 connected to would disable both ROM IC2 and the Spectrum ROM via isolating diodes DIO and D9 respectively 1 4 Gate Array ICI 141 major functions of are to control the following a RS232 serial link b network c microdrive 1 2 1 4 2 is clocked at 8 0 MHz from its own external crystal oscillator on pin 5 and 15 controlled by the Spectrum CPU which uses a standard three bus input output arrangement These busses are the address bus data bus and control bus 1 4 3 Address Bus Addresses AO AIS are decoded to select particular port or memory addresses depending on the required function Eight of these lines are decoded in IC3 as previously discussed 1 4 4 Data Bus DQ D7 constitutes 8 bit bi directional data bus used for data exchanges with the CPU or memory Parallel data input output on this bus is converted to from serial data within since all input output devices connected to are serial data devices 1 4 5 Contro Bus This is a set of individual signals which organises the flow of data on the ups and data busses MREQ indicates that the address bus holds a address for a memory read or write operation The RD and WR signals indicate that the CPU wishes to read or write data to a memory location or device IORQ the input output request indicates that the address bus holds a valid address for the gate a
15. e use a workshop serviceable unit NOT one returned by the customer ZX INTERFACE The following are a number of tests to verify the operation of the various functions of the ZX Interface unit The Interface 1 should be connected to a known good ZX Spectrum or Spectrum and a known good ZX Microdrive a After switch on key in PRINT p ENTER which should give the message Variable not foundl Then key in RUN ENTER The message Program finished should appear This indicates that the paging mechanism is working the ROM is functional 1 2 and IC3 are functional and that at least parts of the ULA and most of the connections to the Spectrum are good If the message appears this means that the ZX Interface 1 Is not functioning or not connected 3 1 2 tr 30 a 50 70 SO 85 ae Ara 33 100 3t 140 50 EO 200 LET 220 ou b E BE Key CAT 1 ENTER If the red LED the microdrive lights and the motor spins briefly this indicates that pins 29 32 37 and 38 of the UL A are functioning properly To test the RS232 and NET ports plug into the RS232 port a D connector with pins 2 and 3 shorted together and pins 4 and 5 shorted together Then run the following program eo rescue DEBA Firs mer Ps M oa i rt i kw k k F OUT eat iis aut HEFT ae DOS THE GPM TO Ux TM
16. e control circuit the microdrive circuit diagram contains one stage of a shift register a flip COMMS CLK is connected to each microdrive and COMMS OUT is routed via the expansion connector to the COMMS IN pin on the next microdrive which is the input to the shift register To select a U U miaradrL a is shifted into its shift register to give COMMS OUT not only feeds the next microdrive it is used to select its own 1 internal functions and to select the LED the motor the erase current and the write protect for the selected microdrive Therefore while this signal is low the motor is disabled the LED is off no current can flow through the microdrive switch and therefore no erase current can flow Consider the motor drive circuit high on pin 20 of Id turns on Ql This pulls the base of Q2 low turning it on and switching power to the motor Capacitor CIO and resistor R2 time constant ensure that the motor does not cut in too quickly and damage the tape The red indicator LED D5 1 switched on at the same time With Q2 turned on and the write protect microswitch closed the erase head current circuit is enabled via pin 6 of the headboard connector When the erase output is enabled on pin 35 of Id transistor Q9 switches on and current flows in the selected microdrive erase head Diodes D3 and D4 provide protection against reverse currents Diodes Dl across the erase head and 02 perform
17. e head spring needs adjusting this is done as follows 1 Unscrew the motor and push the head spring downwards each side of the head to achieve the dimension shown below ii Replace the motor and set its position with the motor location jig 4 3 Ihe two problems associated with faulty mechanical operation of the cartridge are burrs on the head springs and a weak clamp spring Both faults prevent the cartridge from being firmly pushed into the drive position and can cause intermittent operation tape spill etc 4 4 Burrs on the head springs may be filed off using a small flat instrument file Take care not to damage the drive roller on the motor side 4 5 Ihe clamp spring may be bent back into position using a pair of bull nosed pliers Ihe final position of the spring should be within the diameter of the adjacent head assembly post MtN Omm 0 15mm MEASURED TO HIGHEST POINT OF SPRING ON BOTH SIDES HEAD SPRING REFERENCE DIMENSION Sub Section k 1 1 SECTION 5 PARTS LIST LIST OF CONTENTS Page No Introduction ZX Interface 1 Table 5 1 PCB Assembly Table 5 2 Case Assembly ZX Microdrive Table 5 3 Head Board Assembly Table 5 4 Base Board Assembly Table 5 5 Head Chassis Assembly Table 5 6 Case Assembly ZX Interface 2 Table 5 7 Assembly N OO OO P INTRODUCTION The following parts tables 1156 only those components considered practicable to renew The m
18. from polystyrene to ceramic axial purely for convenience of production The value of Cl and C2 has also been changed from 150 pF to 22 pF This value change should be checked for and if necessary fitted retrospectively A 47nF capacitor has been added between pins 9 12 of ICI This is a decoupling capacitor which prevents high frequency interference d The microswitch positioning peg has been moved 1 2 mm towards the edge In early issues the microswitch moving arm can be bent by rough use causing incorrect switch operation e The ratchet roller ratchet and ratchet spring Fig 4 1 have been replaced by two rollers one rubber and one plastic which operate more simply and economically The ratchet is designed to stop a loop forming in the tape as the roller is turned mechanically by the action of inserting the cartridge the drive position the cartridge disables the ratchet A ROLLER nal T PLASTIC ROLLER DRIVE ROLLER VIEW HEAD SPRING HEAD DRIVE ROLLER RUBBER BURRS ASSEMBLY HEAD ASSEMBLY WITH PLASTIC ROLLER POST UNDER BN CLAMP rx ki Em SPRING es 7 MICROSWITCH 1 9 RATCHET 1 USED ONLY WITH N RATCHET SPRING J RATCHET ORIVE 2 4 3 1 3 1 1 2 2 3 2 1 harder material has been used for the clamp spring It has been found that the original material did not retain its spring and sometimes reg
19. icrodrive record playback 1 not listed neither are the side head and ratchet springs TABLE 5 1 ZX INTERFACE 1 PCB ASSEMBLY Circuit Value Rating Manufacturer Notes Reference Tolerance Type CAPACITORS C1 C2 16V Electrolytic Axial C3 1 5 50V Ceramic Axial C4 22 pP 5 50 Ceramic Axial C5 47 nF 80 20 50 Axial ATUF 16V Electrolytic Axial C7 C8 330pF 10 50V Tayol sxtat COIL L 22MH 041 A DIODES D1 D2 157 Rectifier D3 D4 IN4148 Signal D6 to 08 43V 500 mV BZX79C4V3 Zener D9 to DII IN4148 signal continued TABLE 5 1 ZX INTERFACE 1 PCB ASSEMBLY Circuit Heference INTEGRATED CIRCUITS ICI ULA IC2 ROM IC3 4 RESISTORS R2 H3 H4 R5 R6 R7 R8 R9 RIO RII R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 Value 1KO 1KO 3K9 1KO 3K9 47R 3K9 10KO 1KO 12KO 680R 1KO 12KO 3K9 2 7 680R 1KO 2K7 10KO 3308 330R 4K7 10KO Rating Tolerance 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25U 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 0 25W 5 5 Manufacturer Type General LA15 302 Motorola SCH9288 OP 74155260 T4HCU04N Carbon Carbon Carbon Carbon Carbon Carbon Carbon Notes Alternative 5 Texas TP1S4764NLZA 62408 continued TABLE 5 1 ZX INTERFACE 1
20. lowing table lists possible faults and remedies SYMPTOM REMEDY Software does not load 1 Check for low on pin 20 and pin GO OP ICL If high renew IC3 2 Renew IC2 3 Renew ULA 10 Software does not run and Renew one of the following messages displayed File not found Microdrive not present 3 4 ZX Microdrive 3 4 With the ZX microdrive connected to a serviceable system apply power Establish that on board voltages are correct by carrying out the checks set out in the table below VOLTAGE CIRCUIT REF VOLTAGE VALUE 5 V Pin 11 5 7 9 5 no discernible ripple 49 V Pin 10 of ribbon 49 V connector 3 4 2 Perform the ZX Microdrive tests described in Section 3 para 3 1 3 2 Ihe following table lists possible faults and remedies For detailed diagnosis use the test in Section 3 para 3 3 as required SYMPTOM Messaye Microdrive not present displayed If program stops during Write test Read test Message Write protect broken displayed Microdrive does not operate although selected correctly Tape being looped out of cartridge causing Jjarmiing Tight cartridge tape Broken tape Head failure LED failure REMEDY 1 Check and or replace 02 2 Renew ICI 1 Check R4 RS 2 Renew ICI 1 Check Cl C2 2 ICI 3 Renew whole unit Check microswitch a Check motor b Check microdrive mechanics for 1 Burrs
21. nd handling devices must be properly earthed in order to avoid damage resulting from electrostatic discharge ZX INTERFACE 1 Turn the interface upside down and remove 5 cross head screws securing the top cover to the base Lift the base clear and place on one side Remove two 5 8in self tapping screws used to secure the interface to the Spectrum and turn the interface right side up on a clean work surface Remove the 2 cross head screws securing the printed circuit board to the top cover and while restraining the edge connector ease the top cover clear Assembly is the reverse of disassembly remembering to replace the 5 8in self tapping screws the recesses provided BEFORE fitting and securing the base ZX MICRODRIVE Using a small blade screwdriver carefully lift one corner of the adhesive cover trim Having partially separated the trim from the cover remove it completely and discard Remove two cross head screws previously obscured by the trim and after releasing a tongue positioned along the back edge separate the top cover from the base NOTE LED affixed to the cover is connected to the base p c board via flying leads These prevent the cover and base being separated entirely 2 4 324 3 3 4 1 4 2 renew the motor assembly or components on either p c board it 15 advisable to separate the base from the head chassis and base p c board by preceeding as follows Remove 2 cross head screws securing the base
22. neral purpose d Head cleaner Open market e Motor location jig as shown TAP m312 POTIONS FIX s REWS 19 OTE Ka ET RES MOTOR LOCATION JIG 4 1 12 2 1 22 2 9 For details of how the ZX interfaces and 2 and the ZX microdrive connect to the Spectrum and for Spectrum operating procedures refer to the relevant manuals which accompany each unit MODIFICATION HISTORY ZX Interface 1 small number of the EPROM version of the ZX interface were produced This version is characterised by a socket mounted EPROM in IC2 position and by IC3 and ICA mounted pickaback fashion CAUTION This version has no keyway on the microdrive edge connector Take care when connecting a keyway less ribbon connector otherwise a short circuit could occur Where 06 and 09 are Ferranti type 184 these are inserted in the opposite orientation to the pcb legend ZX Microdrive A number of modifications have been introduced on the microdrive These modifications and the reasons for their implementation are summarised below a 22uF capacitor C7 has been added across Q2 base to collector This allows the motor to build up to running speed rather than change rest to speed immediately with the possibility of damage to tape This modification should be checked for and if necessary fitted retrospectively b Capacitors Cl C2 C6 and C8 have been changed
23. ny component has been removed the p c board should be examined carefully to ensure that there no solder splatters which may cause short circuits between tracks or connector pins f Disassembly assembly instructions are given in Section 2 4 2 Actions to take to rectify problems encountered in the mechanical operation of the microdrive are set out in the following paragraphs Replace the motor as follows a Insert the motor and loosely assemble the fixing screws b Insert the motor location 114 to position the motor Tighten fixing screws NOTES 1 When renewing the motor also renew the plastic and the rubber drive rollers If the motor has a combined rubber roller and ratchet discard complete ratchet assembly and replace with the rubber and plastic roller 2 The gap between the rubber roller and the plastic roller should be 0 25 millimetre q Perform the following motor drive test 1 With a cartridge inserted and the motor running push the cartridge gently away from the motor drive roller until tape movement ceases 11 Release the cartridge It should return under the action of the clamp spring and tape movement restart without any rattling or noise If this is not the case then provided that the clamp spring is set satisfactorily the head spring must be adjusted as follows Never adjust new type clamp spring which has a loop below chassis level the motor drive test above indicates that th
24. o the DATA 1 and DATA 2 outputs from on pins 24 and 19 These signals are routed to the interface within the gate array via microdrive edge connector J2 signal recorded on magnetic tape is at the greatest when the rate of change of the signal imposing it was at its fastest Therefore when a squarewave has been written the greatest recovered voltage is obtained on the edge of the pulse Since the object is to produce a waveform which changes at the peaks of the recovered signal contains amplifiers to bring the signal up to the required level and a peak detect circuit which changes state when the input reaches its greatest level The peak detector is followed by a hysteresis circuit which ensures that the output does not change on spurious signals The gain of the circuit should not need to be changed as only one type of high quality video tape is used reproduce signal levels may be read across capacitors Cl and C2 and are typically in the order of 400 mV to 500 mV and 250 mV to 350 mV for the low frequency and high frequency signals respectively In the record mode the modulator in converts the ones and zeros in the data into FM frequency modulation where there is always a transition at the beginning of the bit cell If the data is one there is a transition at the beginning and in the middle of the bit cell which means essentially that the frequency doubles if the data contains ones The gain of the ci
25. rcuit can be adjusted if necessary by changing the ratio of resistors R9 and R8 on pins 15 and 14 of ICI Consider a write cycle When the R V signal from the gate array goes low the selected microdrive is placed in the write mode This has the 1 7 3 1 2 2 3 3 3 4 effect of changing DATA 1 and DATA 2 on ICI from outputs to inputs These inputs are used to drive current sources for track and track 2 When DATA 1 is high for example current is pulled in one direction through the head when it is low current 1 pulled in the other direction Writing is done with an asymmetric write current Because the erase function is carried out with a d c field it is necessary to write harder in one direction than in the other to overcome residual magnetism Resistors and 5 on pins 11 and 7 of are chosen to allow this action Should a different tape be introduced or a different head type be fitted these resistors would also need to be changed ZX INTERFACE 2 The ZX interface 2 connects directly to either the ZX interface 1 module to the Spectrum expansion connector It provides the interface for any joystick that has a standard 9 way D plug and enables the use of ZX ROM cartridge software It also enables joysticks to be used with cassette loaded programs and provides connector for a ZX printer The interface comprises printed circuit board upon which are mounted a single integrated circuit and all the input o
26. rray during gate array input output operations The AIT signal is used to instruct the Spectrum to wait until a looked for signal arrives on the network 1 4 6 Port Addresses The following table sets out the port addresses and individual bits which control input output operations These ports and bits may be addressed in BASIC from the keyboard ADDRESS PORT BIT 7 6 5 1 j 2 0 DECIMAL lt MSB gt BIT LSB STATUS READ BUSY DIR GAP SYNC WRITE EF 239 PROTECT CONTROL WRITE WAIT CTS ERASE R W COMMS COMMS CLK DATA MICRO DRIVE Accessing this port from BASIC will almost E7 231 DATA certainly cause the computer to crash RS232 READ TXDATA NET F7 247 NETWORK R232 INPUT DATA INPUT NET WRITE OUTPUT RXDATA I O PORT ASSIGNMENTS FOR INTERFACE 1 1 5 65232 Serial Link 1 5 1 The same pin on pin 33 is used for the network transmit data and for the RS232 transmit data In order to select the required function IC uses its COMMS OUT signal borrowed from the microdrive control when the microdrive is not being used This signal is routed from pin 30 to the emitter of transistor Q3 and via resistor R4 to the base of transistor QI When COMMS OUT is high Q3 is enabled thus selecting RS232 and when it is low QI is enabled selecting the network 1 5 2 The RS232 link provides a signal of 12V This is obtained directly from the Spectrum via pin 22B on the expansion connector and the 12V is derived from
27. s a latch which asserts the outputs on pins 7 ROMEN and 6 of ICI which enable the interface 1 ROM IC2 and disable the Spectrum ROM respectively 1 2 3 At this time the new software examines the content of the machine stack produced by the original error indication it recognises one of its own instructions it takes over If it sees a genuine error it passes control back to the Spectrum via a message on the data bus 1 2 4 Transistors 010 and control the IORQ line input to the Spectrum ULA pin 33 The IORQ line from the Spectrum CPU supplies both the interface gate array and the Spectrum ULA and is an active low signal 1 2 5 When IORQ is asserted from the Spectrum the Spectrum s own ULA may inhibit the CPU clock for several cycles Transistor 010 disables this action for any transaction except for those during which is low ie I O transactions with Spectrum ULA This transistor is duplicated inside the Spectrum in later issues Transistor is provided to speed up the propagation of IORQ from 780 to Spectrum ULA This is necessary to overcome the extra capacitance on the processor bus and particularly on IORQGE 13 Interface 1 ROM IC2 1 3 1 the additional software needed to operate the interface 1 functions resides IC2 IC2 enable is discussed in paragraph 1 2 2 above In addition to control from the ROM may be disabled by a device connected to the expansion
28. s via the RS232 serial data link ZX interface 1 also provides an extension to the Basic Spectrum software which incorporates all the microdrive RS232 link and network functions block diagram of the unit is given in Figure 1 1 The circuit comprises 4 integrated circuits These and their major functions are set out below a 1 4 oscillator for b IC3 address decoder to page ROM IC2 c IC2 ZX interface 1 ROM d gate array controller of microdrive RS232 serial link and network 1 1 Oscillator and Buffer 1 4 111 1 4 is a fast CMOS integrated circuit which forms with crystal XI a clock oscillator for the gate array It provides a very high drive level to with a very high slew rate 1 1 2 The link shown on the circuit diagram between pin 5 and capacitor 15 included so that the circuit can accommodate some time in the future a self oscillating replacement for ICI 1 2 Address Decoder IC3 1 2 1 The function of IC3 is to enable ICI to substitute the interface 1 ROM IC2 for the Spectrum ROM whenever an error code 1 generated by the Spectrum BASIC 1 2 2 In normal operation the Spectrum program transfers to address 8 when it finds an instruction it does not recognise and an error message is displayed on the screen With interface 1 connected the Spectrum software brings up all zeros on the address line inputs to 3 forcing input pin 3 DECODE on IClJiigh This signal set
29. signals is described in the following paragraphs ZX MICRODRIVE Figure 13 The ZX microdrive is a floppy tape system used to store and retrieve up to 100 k bytes of information per cartridge It is connected to the Spectrum via ZX interface and its own flexible ribbon cable and houses all its own read write and motor control electronics within its case Expansion port connectors on each microdrive allow up to 8 devices to be plugged together and connected to one Spectrum computer 1 5 2 2 P 2 4 252 2 6 1 The microdrive cartridge uses a continuous loop of 2 mm wide video tape Data is written on two tracks using a standard stereo head arrangement and is written in bytes one byte to each track Data 15 read from the tape in the same way Software sees the tape as one continuous track since hardware takes care of switching between tracks Although up to 8 microdrives can be connected together and controlled from Spectrum only 1 can be in use at any instant The required microdrive and the type of operation read or write is selected under software control During a read operation data is read from the selected microdrive tape During a write operation the microdrive tape 15 erased before being written The erase head is displaced from the write head and is timed by ICI to sink current before the write head is enabled Microdrives are selected using the COMMS OUT and COMMS CLK signals from Each microdriv
30. similar functions The amount of current flowing in the erase head is limited and is about 25 mA The write protect signal WR PROT on pin 32 of gate array 15 normally low selected microdrive pulls this signal high when the WR PROT microswitch is closed When the microdrive cartridge is not present or the write protect flange is broken off this signal is low informing the user that it cannot write 1 6 2 8 249 2 10 2 11 2 12 2 13 2 14 29 During read write operations the R W signal on pin 23 places the selected microdrive in either the read or the write mode and enables the read or the write amplifiers Data is recorded on 2 tracks using a standard stereo cassette head arrangement and is written in bytes one byte to one track and the next byte to the other track It is recovered in the same way tape itself is one continuous loop Since hardware takes care of switching between tracks the software sees the tape as one double length single track Power to the microdrive circuits has to be filtered and IC2 and capacitors C3 and C4 are used to accomplish this Consider a read cycle the read mode the signals appearing in the two read coils inside the heads are differentially amplified through two amplifier chains within signals are then converted to digital form to enable logic processing outputs from the 2 amplifiers in digital form are enabled int
31. the output of a charge pump formed by diodes 01 and D2 and capacitors Cl and C2 The output may in fact fall as low as 7V but since the RS232 interface specifies 3V this is adequate 1 5 3 The RS232 serial data interface can be sent 2 types of data 8 bit 1 5 4 1 5 5 binary code and 7 bit text only information Refer to the interface 1 manual for details The RS232 employs 4 data and control lines as set out in the table below LINE FUNCTION IC PIN Rx DATA Receive Data Transmitted data 33 Tx DATA Transmit Data Received data 4 CTS Clear to Send Tells remote station that Spectrum wishes to send data 34 DTR Data Terminal Ready Tells Spectrum that remote Station wishes to send data 1 In operation serial data prepared in the Spectrum is transmitted to line via transistors Q3 and Q4 These form an amplifier which produces a large voltage swing The same circuit is used for the transmission of the CTS signal using transistors Q6 and Q5 The Tx DATA and DTR signals received from the line are fed into a terminating and clamping circuit formed by resistors R24 and R25 R28 and R29 and diodes D6 and D7 Negative excursions of signals are prevented and the signals input to ICI are limited to 45V The RS232 interface is output on a 9 pin connector SKI which provides a ground signal and a pull up signal This allows for a high level signal to be fed back into DTR when the remote device does not provide a DTR signal 1 4 1
32. uired to be bent back to its original position Where is Ferranti type BCI84P this transistor is inserted in the opposite orientation to the pcb legend ZX Interface 2 problems have to date arisen with this unit 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 Since the number of discrete components is limited it 1 possible that the major source of faults will be within integrated circuits However before any 1 1 chanyecl waveforms and levels in the circuit must checked 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 following pages provide a basic fault finding procedure and a list of possible faults along with suggested remedies As matter of course the suspect board should be inspected for obvious faults such as burnt out components or raised tracks Edge connector pins should also be cleaned either with an eraser or an appropriate cleansing agent applied with a small stencil brush and wiped clean with lint free cloth Pin connections should be inspected for
33. utput connectors With the interface 2 connected to either the Spectrum or interface 1 and with a ROM cartridge inserted the signal disables the Spectrum ROM and enables the Spectrum to interface with the cartridge The Spectrum CPU then uses its address data and control busses to access the ROM via the expansion connector The interface 2 ULA is a custom built CMOS integrated circuit which plugs into the p c board mounted socket Figure 1 4 gives a schematic of the device Address bits AO and Al2 are used to address the 2 joysticks with IORQ W performing their standard control functions Lines Kl to receive the control inputs from the 2 joysticks The functions and connection details are summarised in the table below PIN NO SK3 SK4 FUNCTION K9 K4 UP DOWN 3 K6 Kl LEFT E K2 RIGHT 6 KO K5 FIRE 7 0V COMMON NOTE Kl to K9 correspond to keyboard keys 1 to 9 Leo The rear edge connector provides connections for a ZX Printer POWER SUPPLY The Spectrum power supply is capable of driving the Spectrum interface 1 interface 2 ZX printer and 8 microdrives at the same time FIG 1 1 INTERFACE 1 AND MICRODRIVE BLOCK DIAGRAM x HLAS 0 EPECTAUNI in nA 1 w w 1 xi LE nale 4 4 if al Iu CIMM COMMS CLA WA 8415 amp 1j
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