PAﾘPGA - BAL4U
Contents
1. E Temperature Range e Electrical Characteristics 7 fv DC Supply Voltage Voo Counter i led V Go 7 fv Operating Top 35 85 C Temperature Range e Maximum operating frequency Rating Symbol Condition Min Typ Max Unit Count frequency Voo 4 75 MHz Fin Vi 1Vp p Table 1 MSM5524 CONTROL 3 2KH2 O STOP WATCH x 3 AM BC OUT z gt 6 O PM FM OUT 2 NS SEG A TT be A o SEG B 35 o SEG C o gt va EG D K gt o SEG E og o SEG F o f 9 eo De SEG G 88 OFF TIMER point SLEEP BE o o 7 Db e 0 10 w ata o 10 E co 10 O a vw Sp D net eur JE w v sr v t O TIMER OUT Fig 2 MSM5524 CIRCUIT DESCRIPTION MSM5524 The equivalent circuit and electrical characteristics of the MSM5524 are shown in Table 1 and Figure 2 respectively 1 Display Drive Output The display drive output dynamically drives a five digit common anode display element Segment outputs are present at pins 25 31 while digit outputs are present at pins 2 6 The active state of each segment H and digit L requires an output current of 1 mA and 2 mA respectively which are supplied by drive transistors O35 039 2SA1015 Y Function display outputs are assigned to each pin as follows Pin 35 Point Pin 34 AM and BC Pin 33 PM and FM Pin 32 Stop watch These operation mode display elements are driven by transistors2. I could see that here had been a very fustrated amateur at work who had Le turned on every coil and trimmer in the process making more trouble than he started with After re alignment the PLL board was working again but now the VFO was not working well JK When I tested the output with the counter I found that the output wire in FR i the connector was broken so I had to repair the connector NE Now I had signals on every band but had another curious problem On USB or LSB I had signals but also a steady tone of around 3khz independent of the incoming signal It seemed to me that both sideband oscillators were running at the same time but I could not see how because the sideband switch was working correctly After pulling the board i out I discovered that there was a solder connection between the power pins of the two isuliatore so they worked at the same time Maybe a previous LAS es wa owner didn t like to switch between USB and LSB While the board was out I desoldered the MSM 5424 and the 74LS196 IC and put them in a socket Close inspection discovered some more shorts between solder joints The OM who worked on this receiver was clearly not qualified to work at this kind of equipment and has a BIG soldering iron After reinserting the board I had now signals at all bands The remaining problem was now the counter and the clock The counter displayed only a righthand zero the clock was partially working the A
3. Q42 and 43 2SC1815 DISPLAY SELECT ee fe Mii Clock Timer CI CI CE re CA CN ES IE Frequency Counter H Voo level or open L ground level Table 2 Function of indicator selection terminal ce TR an Resets to AM 1 00 005 2 Time Correction Pins 38 A and 39 B accept time setting inputs which are active at L level Placing these terminals to LU level permits the functions shown in Table 3 in accor dance with the mode selected from Table 2 Each time the time correction button is depressed in crements the clock display by one hour or minute When the button is depressed for more than 1 6 second the clock display is continuously incremented at a rate of 10 Hz Other Pin Functions a Pin 23 AC All clear input Initial clear is accomplished by groun ding this terminal through capacitor C198 0 047 uF when the power to the unit is turned ON b Pin 22 BLANKING Input logic of this pin is active at level H When this pin is set to H all the outputs except the timer and sleep outputs are inhibited It is usually set wm TL c Pin 11 DIMMER This pin accepts the command signal that causes to reduce display brightness When this pin is set to HK active the display output pulse width is reduc ed to one fourth d Pin 20 FIN This pin accepts the frequency counter input signal Function rile Advances the minute maintains the minutes and counts the
4. condenser and is brought out of the VFO together with the 3 existing wires This wire has to be some 10 cm longer than the others The variabele voltage from the fine tune potmeter is on pin 13 of Plug 34 this plug is not connected if you dont have a memory module so we can solder a pin to the end of the VFO wire isolate everything with crimping tube and plug this pin in position 13 of P34 For the pin I used a old wirewrap connectorpin it has the rigt size The wire of pin 13 has a white violet color See pictures from this mod If you should obtain a memory module the only thing you have to change is pulling the wire off the plug and connect the plug to the memory module This modification is very elegant because there is no drilling or extra knobs necessary simply undone if neccessary easy to use and has no side effects in stability of the receiver I can recommend this mod and have now done it to all my FRG 7700 s except one who had the memory module installed Another set of modifications are described on a very interesting Swiss internet site The adress Is http www dr boesch ch radio yaesu frg7700 modi htm You find very much interesting stuff there about ham equipment and a lot of very good descriptions of ham equipment The pages are in German so I will give a translation of the mods for the benefit of all of you who are not fluent in that language I did only the listed mods on the receiver board there are some more on t
5. epoxy experiment board see the pictures and schematic below The LM 317 makes the construction very easy and the output to the rx is adjustable to exact 11 Volts I put in a couple of protection diodes over the LM 317 for safety reasons The 2k2 resistor is a trimmer The powersupply works fine and stays much cooler than the original one After a day on there is no warming up and Stability of this receiver is now the best of the lot After connection of the power supply the receiver seemed to work it had a hissing sound and after much searching the display did nt work the bandswitch was not in the right position and the P S UNIT 003 S2V 10 2SC945AQ analog dial was off scale I found a station in the 13 Mhz commercial band that I recognized and oor saveur after confirming with another receiver I was able ok D1 02 to calibrate the analog dial and put the oe BI Fra ee bandswitch knob at the right position Well that ee a mal 150 was the only band with signals but at least there o p F y was hope for the better ne ag After a careful inspection of the PLL board I saw 3 E 5 that the bandswitch had been tampered with the switch had been removed and resoldered but The changes in the powersupply several print traces were pulled off and repaired a ee ss te _ IN 2 11 with some wires
6. ragchewing Hams The ragchewers are not always at exactly the same frequency and constantly tuning with the main dial is no fun because you easely overcompensate losing all information The main dial can be set exact enough but not quick enough to follow quickly changing talk A FRG 7700 with a memory unit has no problem with that you tune in push the Memory button and then Memory read You can then tune around the frequency with the Memory fine knob After studying the circuit diagram I found that the Memory Fine potmeter is nothing more than a voltage divider the output is used to tune a varicap in the memory unit Well why not tune a varicap in the VFO with the existing circuit I did it this way in a home brew transceiver some 25 years ago and that worked fine So I took the VFO out the receiver a very easy job altough it means the removal of all Knobs scales and front panel Be careful with the lampholder on the VFO see above disconnect everything including the power cord IOP Us CIO A AS ic CI2 RIS LO3 VCO CO 2400P PB 2172 No 3 VFO UNIT RIO RII RI6 gt 100 100 100 S x x 8 e 3 SA O co7 E RS 28 PE y E Ee cos F7 0 O x O 8 00 lt S Rs 001 33 p a SL boa og OF L 42 I An gt ter qa P34 yu re 13 I then build in the VFO a small circuit with a VHF varicap that was on hand BB 209 and a small ceramic condenser 12pf over t
7. seconds Advances the hours maintains the minutes and counts the seconds on Norma operation L Resets to AMO 00 ON TIMER ora Advances the minutes and maintains the hours H Advances the hours and maintains the minutes os Maintains the timer ON time When the timer QN time ts reached pin 24 turns ON L Reset to AMO 00 OFF TIMER CB Advances the minutes and maintains the hours DIO Advances the hours and maintains the minutes PH Maintains the umer OFF time When the timer OFF time is reached pin 24 turns OFF Dropping A or B to L advances one digit When the or B is kept at L for more than 1 6 seconds the digit advances continuously at a speed of 10 Hz Table3 Function chart of input A B Ex West La p Te etter Aor sats miia ie TL en af PET bel Le aus p as A FRG 7700 adventure a resurrection story of a FRG 7700 I had a recently a receiver with a bad displaydriver and obtained another from Internet as spare with a defect Well as things go this rx had also a display problem the previous owner told me that he had used the receiving and PLL board himself for a swap because the powersupply of his had blown up so I expected that I had just got a bunch of spareparts for my other receivers After much searching I found a source for the MSM 5524RS and repaired the original receiver and after de
8. solder them to the existing long wires after cutting away the old bulb using isolation tube or crimping tube to isolate the wires and joints That way you don t have to remove the metal frontplate for access to the soldering joints Be Careful Remove the powercord first The lamp of the VFO is mounted in a small reflector that is very close to the soldering side of the receiving board and this lamp is always glued to the grommet from the heat of the lamp so changing is very difficult To get access you have to disassemble the front panel and the analog dial During the change it is easy to bend the reflector somewhat and make a short to the board destroying the counter clock ic in the process because the IC and part of the powersupply is On all the time It is really necessary to remove the power cord otherwise you do not remove all the power with disastrous results Displaydriver IC MSM 5524RS If the display is not working there can be several problems but the most common is the failure of the big driver IC the OKI MSM 5524RS or the surrounding switching circuit The MSM 5524RS is a 40 pin LSI chip with a clock dual timer on off time a countdown timer for 60 minutes and a 5 digit frequency counter which is used in this receiver for the display of the received frequency The MSM 5524RS drives a 5 digit fluoricent green tube multiplexed digital display for clock and frequency A mode switch changes the display for f
9. 0 asc No past mes mo Ml Fe MODE p Gan gt TONS am Es o POWER PHONES REC il Use ca ROO VED
10. 0microhenry minichoke for a better decoupling of the mixer 14 8 9 10 11 12 Change C94 and C95 all 10nf in inf for a lower load of T09 and T10 Remove R85 4k7 for a better Q of T09 If step 8 and 9 is done you have to re align T09 and T10 for maximum signal Change C89 C101 C111 and C117 all 10nf to 560pf to lessen the load on T08 T10 T11 and T12 Remove R65 12k to raise the Q of TO5 Remove R124 10k to raise the Q of T13 It is possible to remove also R115 10k but the gain and noise of the 2 TF will raise to high level and can cause oscillations So it is not recommended You can change the IF filters for better ones a recommendation I did not change any 13 14 CFO1 CFW 455HT or CFG 455H bandwidth 6khz CF02 CF 455k6 or much more expensive Icom FL44A 2 3 khz CF03 CFS 455J 3khz CF04 CFS 455H6 6 khz Change C164 470 uF to 47 UF for a higher pitched audio Personally i did not like the result and changed this elco back to 150 uF Solder a 330nf condenser parallel to C158 100nf for a better tone correction Again I did not like the result and changed C158 to 270nf This last part is a pure audio modification and makes the audio somewhat higher and gives a better SSB signal but for SW broadcast the audio quality is good as is and need no changes ri ES M o This is the resurrected FRG 7700 in my shack COMMUNICATIONS RECEIVER vaesu fRG 770
11. COMMUNICATIONS RECEIVER YAESU FRG 7700 PHONES REC o Y Yaesu FRG 7700 SPECIFICATIONS Frequency Range Audio Output 150 khz 30 Mhz in 30 bands 1 5 Watts 8 ohms 10 THD Modes Speaker Impedance AM SSB USB LSB CW FM 8 ohms 4 16 ohms for external speaker or headphone Sensitivity AM SSB CW FM 0 15 0 3Mhz 30 UV 3 UV 500 ohm n 0 3 2Mhz 25 uV 2 UV 500 ohm 2 30 Mhz 5 UV 0 5 uV 50 ohm 1 pV 50 ohm Selectivity 6 db 50 db AM wide 12 khz 25 khz AM medium 6 khz 15 khz AM narrow 2 7 khz 8 khz SSB CW 2 7 khz 8 khz FM 15 khz 30 khz 40db Stability Less than 1 khz from 1 30 minutes after power on Less than 300 hz after 30 minutes warm up Antenna Impedance 0 15 2 Mhz BC 500 ohms unbalanced 2 30 Mhz SW BC 50 ohms unbalanced Power Requirement 100 110 220 240 Volts AC 50 60 hz Power Consumption With Memory Unit Standby 10W 10W ON 33W 39W 12Vdc 850mA Size 334 W x 129 H x 225 D mm Weight With memory unit Approx 6 kg 6 5 kg PA PGA ia q ni ERR ad a FRG 7700 Survival guide Av GET pen nina EN EE nt e ET nn a tt lider BLUES COMMUNE ATOMS RECEIVE TERME Caen somrene FRE 7700 POSES una i rea md MIF POE REC ef 3 PAn n JE This is a survival guide for the FRG 7700 one of the most versatile receivers from Yaesu With the help of this guide your Frog can survive the next 20 years and mor
12. M Led was on all the time the ON and OFF timer had the same time only the countdown timer was working My first impression was that the clock counter IC was defective I tested the counter amplifier and discovered that the 74LS196 dit not get a proper signal The first 2 transistors of the amplifier were working but then things went wrong so I took the board out again to change the transistors but after close inspection I found that the BIG soldering iron has been there also and made a short between collector and base of the third amplifier transistor After correction of this I had a signal at the 74LS196 IC and surprise had now also a 3 digit frequency display The displayed frequency was the counter input without the IF offset of 455khz and divided by a factor 10 I had the counter still connected So it seemed that the counter IC did at least something The Xtal oscillator was working and at the good frequency Mode switching is done at pins 7 8 and 9 so I checked the in and outputs of the IC and found that pin 8 was no true zero I checked again the mode switch which was ok and the diodes D42 D43 D44 who are used for switching Bingo D43 was defect and displayed a resistance of 5 K ohm in both directions The diode wires were very corroded so I changed all three diodes I found out afterwarts that this receiver was used on a sea going yacht and some spots were corroded from the salt water After changing the diode the frequency displa
13. e This guide is in the true boatanchor tradition a collection of known faults and their solution and a story of resurrection of a receiver at my workbench My command of the english language could be better so I apologise for languistic mistakes here and there I just hope that I could help anybody to maintain his FRG 7700 in good condition 73 Wim Penders PAOPGA Description The FRG 7700 is a compact communication receiver for the reception of AM SSB CW and FM signals between 150khz and 30 Mhz The receiver is very sensitive and stable and has a pleasant audio It has no special bells and whistles but is designed with the shortwave listener in mind That is maybe the reason that the receiver after 20 years is still very popular and in demand by hams Tuning is simple and exact choose band and mode and you are in business No trills and frills listening with this receiver is very basic and you learn to listen instead to play with menus You can obtain a used one in good condition for a affordable price on hamfests or on Internet Be careful if you buy from Internet there are many guys who advertise with a receiver in good condition but when it arrives it is a box full of junk I have a credo here If it is not possible to collect equipment myself and pay cash I am not intersted and can better save my money I have to see what I buy Serial The FRG 7700 was getting to the amateur market in 1981 and is replaced in 1986 by t
14. e display circuit operates on 11 V DC which is created by a DC DC converter The FUNCTION switch has four positions FREQUENCY dis play CLOCK display TIMER ON and TIMER OFF Each time the HOUR switch is depressed increments the clock display by one minute continuously depressing the MIN switch continuously increments the minutes digit of the clock while the hours digit is left unchanged Depressing the HOUR and MIN switches at the same time resets clock display to 1 hour O minute O second and releasing both switches restarts clock operation When the FUNCTION switch is placed in the ON or OFF position pressing the HOUR and MIN switches at the same time resets the clock to 0 00 To preset the timer first preset the desired ON time or OFF time then set the TIMER switch to ON This will turn off or on the power to the unit When the preset ON time or OFF time is reached the power to the unit is again turned ON or OFF At this time the POWER switch may be placed either ON or OFF position A relay contact output interlocked with this timer operation is available at the REMOTE terminal LOAD LATCH See OG raeovener couvre FiNO hos FREQUENCY COUNTER Ce a CE RESET PRESET 1051 BOOH1 IOHr de wer LE s0 122 i f x pa u u wu we N mala ca 90009206 E J OE EG GEBE Te Tic DECODER Tse ari sO Jun jo oecon f se creer nom MSM5524 e Maximum Ratings
15. ext mod project and I will update this page when I have everything figured out Paint You can find now and then a mint receiver on the market Generally speaking the appearance is a sign of how careful the previous OM was with it but most receivers have seen some use and look like it The paint on the frontplate of the FRG 7700 is easely scratched in particular the sides Yaesu did it the cheap way here a spray of metallic paint over the plastic faceplate and that is a pity because it is very difficult to repair I tested with different car repair sticks but was not able to find the right shade paint Most sides of the frontplate are heavely scratched so I will try to paint the sides alone if there is then a small difference in shade it will not be so obvious Removing the paint altogether from the sides is also a possibility it can be done with thinner and rubbing with an old cloth you have just to be careful with the front itself the paint there is quick damaged Thereafter you have black sides which don t look bad and scratches are for the most part invisible I did a test the plastic was not affected by the thinner Painting the front is as a whole is almost impossible the lettering is printed on the front and is easely damaged So I clean everything including knobs and dials with water and soap and a old toothbrush Rub it dry with an old cloth Don t let parts long in the water the aluminium inserts are glued to the knobs a
16. ge is getting lower at the high side of each band a re alignment of the first PLL is necessary receiver receives not higher than 950 or so on the analog scala If only the end points at the 5 12 20 and 29 Mhz bands are too low a re alignment of the second PLL is necessary This alignments are not difficult to do you need a good counter a VTVM RF millivolt meter or oscilloscope and fitting plastic or ceramic tuning tools Under no circumstances use metal screwdrivers for alignment of the coil cores they will ruin the cores Use only fitting plastic or ceramic alignment sets For the trimmers use a small screwdriver or a ceramic one The procedure to align the PLL is described in the Yaesu Operator and also in the Service Manual There are some changes to make in the manual PLL Reference oscillator Adjustment Set the MR switch off and connect a frequency counter to TP04 instead of pin 9 of the MB 84040B ic as the manual says and adjust TC 2002 for a frequency of exact 6 400 Mhz on the counter The result is the same as in the manual but you dont have to work at the ic with the risk of shorting pins The PLL Local alignment can be done as in the book if you don t have a HF VTVM to measure the voltage you can use a HF oscilloscope for this alignment together with a counter However if you do nt have either skip this alignment If you receive signals this section is working Just check for a 47 6 Mhz signal For align
17. he FRG 8800 There is not much difference between the first and the last receivers the only thing I saw was a different coupling of the frequency scala to the dial mechanism In the early versions it was a felt ring in the later version a spring You can check the age of your FRG 7700 if you look at the serial number I have here sn 4E 290421 this receiver is made in May 1984 the first digit gives the production year the second letter the month A Jan B Feb a s o then 3 digits of the production run and 3 for the serial number Another is 1F 070507 this receiver is made in June 1981 Other numbers are M1C 050492 march 1981 with memory module and 1E 060340 May 1981 Manuals Copies of the User Manual and the Service Manual can be obtained from the Fox Tango website by far the best website for all classic Yaesu equipment If you want to work on your FRG 7700 it is a must to have the manuals and schematics See http www foxtango org The manuals are very informative and deal with the use and alignment of the receiver and have a complete partlist Another very good source for free manuals is http www mods dk who has manuals of almost all modern Ham equipment The only drawback is that you are limited to 2 manuals a day On this site are also modifications pictures descriptions and more Recommended Parts Unfortunately after 20 years there is no dealer around who still carries spare parts but fortunately there are n
18. he existing variabele condenser The tune voltage is HF decoupled by a 10k resistor and a 22n condenser I soldered everything spider style to the tuning condenser See picture The only critical part in this mod is the ceramic condenser it must be a type with a neutral temperature coefficient NP 0 black dot After testing the VFO was retuned with the trimmer only to 2500 khz with the variabele condenser fully meshed With the condenser fully open I had a frequency of around 3600Khz The variabele tuning range changes somewhat over the band on the low side the frequency span of the fine tuning is around 12 khz at the high side it is around 3 4 khz but because the fine tuning was meant for the hambands which are all on the low end the variation is more than enough for normal use The stability of the VFO is just the same as before and also the calibration of the analog scale is not affected In normal use I have the fine tuning in the midposition so I can tune either way of the station Should you need a smaller or greater variation just change the ceramic condenser I found that the variation at the low side is around 1 khz pf The reason of the frequency span variation is that the new condenser at the low side has a smaller effect because it is in parallel with the whole main tuning condenser and if the condenser is fully out the added capacitor varicap is doing the job A wire is soldered to the connection of the 10k resistor and the 22nf
19. he powersupply but i did not use them so look at the site eventually I used parts what I had on hand special the minichokes I listed the used ones After modification the receiver is to re align according the service manual for the best results The adjustments are very minor in a well aligned set The original mods were described by Georg Lechner in magazine Weltweit Horen nr 11 1986 Description of the mod The FRG7700 is a half synthesiser half conventional design and is nearly identical to the Kenwood R1000 The circuit design is ok but can be improved The set and memory module is very stable but some changes improve the receiver considerabely 1 Put parallel to the SW socket a minichoke of 100 200 microhenry and parallel with the BC socket a choke of 1 MilliHenry to form a DC path to unload antenna charges 2 Change R3 47 ohm near the antenna plug in 470 ohm to make the attennuator more usable For the rest of the mods it is necessary to remove the receiver board from the receiver 3 Remove RO1 4k7 and R03 470 ohm to lessen the coupling between the BC and SW inputs 4 Change C07 47nf to 4n7 and C69 10nf to 2n2 for lower audio interference 5 Change R46 470 ohm to 330 ohm and put a 500microHenry 1 MilliHenry minichoke in series for a higher collector current of Q1 to Q6 6 Change R60 R61 R76 and R78 from 470 ohm to 330 ohm for a better 1 and 274 mixer current 7 Change R79 100 ohm in a 100 30
20. ment of the first PLL connect your dc VTVM to TPOS in front of the first PLL box and rotate the main dial to the 1000 position of the analog dial Adjust T2007 for a reading of 7 volts on the meter Try to make 7 volts as close as possible Rotate the dial to the 0 position and check the voltage it will be around 2 4 Volts The manual says between 1 5 and 2 0 Volts but none of the four receivers I tested were in that range All of them had higher values from 2 25 3 1 volt and are working fine so I let it at that For alignment of the second PLL connect your dc VTVM to TP03 just in front of the MB8718 ic and rotate the dial again in the 1000 position Set the bandswitch at the 5 Mhz band and adjust T2004 for a reading of 7 4 volts dc Change the bandswitch to the 12 Mhz band and adjust T2003 for a reading of 7 4 volts dc Change the bandswitch to the 20 Mhz band and adjust T2002 for a reading of 7 4 volts dc Change the bandswitch to the 29 Mhz band and adjust T2001 for a reading of 7 0 volts dc Try to make this adjustments very careful often these voltages are too high resulting in a loss of range or a failure to lock properly with a high noise level as result Now rotate the dial to the 0 position and change the bandswitch to 0 6 13 and 21 Mhz position and check the voltage at TP03 they should be between 1 5 and 2 0 volts I measured voltages between 1 45 and 1 70 volts in my sets Be carefully with
21. nd come off if you leave them to long in the water and there is a possibility that the white paint on the knobs comes off too I repair them with a toothpick and white Hammerite paint Direct after filling the lines I sweep the excess paint off with a cloth saturated with white spirit You have then a excellent line The Hammerite paint dries quickly and is very strong I have never had to repaint a knob again I use it also for repainting and refill markings on boatanchor receivers like the R390A and Racal The covers are sprayed twice by Yaesu first a spray of normal paint and then the sides and coverplate were sprayed with a kind of cracle paint In some occasions parts of the second layer flaked off This is very impossible to repair so I clean the plates rigorously and after that use a good automobile wax to make the best of them I like everything clean but some wear and tear is visible after 20 years I have no problem with that if the receiver is electrically sound Don t we have all wear and tear problems hi CIRCUIT DESCRIPTION COUNTER AND CLOCK CIRCUITS The PLL circuit output is amplified by 029 032 2SC1815 Y in the RX unit then is fed to Q33 SN74LS196N where it is divided by ten The divider output is fed to Clock and Counter IC MSM5524 which provides a display output that is reduced in frequency by 455 kHz with respect to its input The master oscillator for the Clock and Counter oscillates at 3 2768 MHz Th
22. ot much special parts used in this receiver and most parts are easy substituted by standard parts The receiver is very rugged and normal used there are not much problems The only parts that can give trouble after longer use are the mechanical parts as switches and potmeters It is not easy to find replacements for them keep an eye open for special parts at hamfests or have a good junkbox with old radio parts I can recommend the Graveyard section on the Fox Tango site they are a excellent source for special parts See for yourself at www Foxtango org Alignment Most FRG 7700 receivers have no problems but after 20 years of use a re alignment can be necessary To align the receiver you have to be very familiar with the used circuits or you end up with a worthless piece of junk if you don t understand what you doing That is true for all kinds of communication equipment I have seen all kinds of junky stuff on e bay that was tampered with and sold for high prices to the chagrin of the new owner Most of the time the problem is a loss of the frequency coverage usually at the end of the tuning scala The receiver has normally a overlap at each range from between 30 to 50 khz at each side from the range for example at 7 Mhz the receiver tunes from 6950 to 8050 khz and other bands have the same overlap at each end The PLL circuit in the FRG 7700 needs some attention if you have the following sympthoms If the end point of each Mhz ran
23. requency clock on time off time and sleep function If the receiver is switched off the display is off however power to the IC is always on The display stays on when the mode switch is in one of the clock modes and then displays the time even when the powerswitch is off The MSM 5524RS IC is the same as used in the Kenwood R 1000 receiver and you can find some info of the chip and circuit diagrams in the R 1000 manual which I reproduce at the next pages There are some things to know about the frequency display The displayed frequency is the PLL frequency 0 455 30 455Mhz offset bij the IF frequency 455khz resulting in a frequency display of 0 000 to 30 000Mhz There is just one offset possible so in SSB mode there is always a frequency difference between the carrier frequency and the displayed frequency of about 1 5 khz because the carrier of a SSB signal is at the lower or upper side of the signal The highest resolution of the display is 1 khz so there is always a frequency difference of 1 2 khz between the true and the displayed frequency This explains the difference in frequency as you are listening to a ham net on a given frequency For AM however the displayed frequency is correct if the received station is tuned in the center of the filter The MSM 5524RS IC is very dependable and when normally used there is seldom a failure You see seldom a R 1000 with a display failure because they use a different board layout P
24. roblems with this IC are almost allways man made like a short during the change of the light bulb in the VFO see above or poking around in the set with the powercord attached If this IC fails you are in big trouble because the manufacturer stopped the production some 15 years ago and supply is very scarce if found at all I saw one used on e bay for a rediculous price around 60 so be prepared for a long search Maybe they have been used in some clock radio s from the eighties but I did not find any yet Your best bet is to obtain a Spare set with a defect display or otherwise and use the good IC Kenwood used the same IC in their R 1000 receiver so that can be a source as well Causes of trouble for this IC are the switch and the switching diodes which choose the mode of operation One of my sets had a bad mode switch Using the clock was no problem but the switch could not change to the frequency mode it still displayed the time The reasons where bad switching contacts in the mode switch I took the switch out and removed the back plate If this is carefully done you can put the switch back together again without problem After a squirt of contactspray and working the switch a couple of times everything worked nice again In another case I found diode D43 that was no diode anymore but a resistor of 5k ohm the on and off time of the display was the same and there was a curious frequency display The frequency displayed wa
25. s the receiving frequency 10 plus 455 so 7455 displayed as 791 so apparently the 455 khz offset was not switched on I changed all three diodes for 1N4448 types because they had a bad oxydation of their leads Later I found out that this particular receiver has been used in a yacht and salt water spray left its corroding mark If you have some weird display problems check those diodes first or the attached switches and transistors Display The display type is FIP 5A8B a 5 digit green fluoricent tube of the kind that is much used in home audio equipment and in practically every receiver and transceiver of the eighties Yeasu uses a amber filter to change the color in the style of all their equipment of the time FT101ZD FT901 This tube has a filament and has in the long run the same problem as all tubes the filament is coated with emitting material but after long use this material is exhausted and the display is getting dim If your display goes weak you can solve the problem temporarly by removing the orange filter in the display window Your Frog has then a very bright green display that will again last for years I tried it but was not happy with the look of it It was no Frog anymore so I put the filter back AM band Under 2 Mhz the FRG 7700 is in my opinion very unsensitive and if I want to do some Dx ing in this band I use my R390A receiver I will try to make my FRG 7700 at least as sensitive it will be the n
26. so I measured the connections and found a broken trace To repair the board it was necessary to take the PLL board out of the receiver While I was at it I measured all diodes and inspected the rest of the board very carefully All seemed ok After studying the schematic I suspected a partially defect MC14504 It is a level translator between the BCD bandswitch memory unit and the MB 8718 programmable divider so I soldered the IC out and put in a IC socket If I got a spare changing the IC was done in no time After inserting the board I checked the bands and now I had several more bands with signals Several bands were there but on the wrong position of the switch 7 000 8 000Mhz was now 12 13Mhz and other bands had also weird switch positions Because the display didn t worked either I put a counter to the counter output of the PLL to have at least a indication of the frequency the counter frequency 455khz is the receiving frequency I made a truth table of the 6 input pins of the MB 8718 and soon discovered that pin 15 had no true 0 or 1 but had always a voltage of 3 15V on it When touched with the multimeter probe the divider switched to the right frequency SO my suspection of a bad MC14504 proved correct and I ordered a new MC14504 After putting it in the socket all bands were now in the correct order FZ I checked and adjusted the two PLL circuits because they were way off the right f org A tuning voltage af
27. soldering the old IC I put the new IC in a IC socket because several times desoldering a 40 pin IC is not good for the quality of the board and the IC In fact I use always a IC socket if I change IC s If they fail once there can be a reason they fail again in the future and putting in a socket is cheap and makes life easier when the need arise The spare receiver didn t look too bad so I decided to try how far I could get with the resurrection of this receiver just for the fun of it After 46 working years I am retired now so time is no issue First I had to construct a new powersupply because the owner had trown away the burned board but fortunately had still the original transformer complete with burn marks and burned wires First of all I tested the transformer after cutting off the burned wires and repairing them with the use of crimping tube and suitable wires The transformer was ok after a day under full load there was no trouble so I decided to use him The transformer is a common type with a switched primary 110 117 and 220 240V the secundary is 12V 2 Amps For the power supply board I had 2 options copy the existing board from another receiver or construct one myself I wanted to use the original features and designed a board centered around a trustful LM 317 regulator IC and a NPN power transistor For the bridge I used 4x 1N5005 5A silicium diodes and the condenser is a 10000uF 50V type I mounted all on a piece of
28. tered where man made by amateurs who never read a handbook but first plug in a soldering iron and sell the set when the smoke has settled and then often try it again with the next set coming their way Troubles I have encountered so far Power Supply There is a source for trouble here the transformer rectifier bridge and condensor 6800u 40V are always on because they deliver 13 5V to parts of the receiver used for the clock and automatic switching at the selected time This should not put too much strain on the powersupply because the current is minimal The source for trouble is the rectifier who becomes very hot so hot in fact that in one case the wires to the transformer caught fire and the condensor exploded Check the soldering joints from the bridge in the board they can have some cratering soldering them trough with a soldering iron is then the solution A change for 4x 1N5405 or another bridge rectifier is also possible If you don t use the receiver for automatic recording of transmissions or for a long time disconnect the set from the mains or mount a powerswitch at the backside of the set that way there is no risk of fire If you have the memory option it is best to use the backup battery adapter Dial Lamps Dial lamps are long lasting but they have to be changed now and then They are 12 Volt 100mA types with long wires and can be obtained in every parts store Eventually you can use bulbs with short wires and
29. the coil cores of the PLL they have been stabilized by a lot of wax which can give some trouble Be gentle you can feel trough the wax for the correct position of the core and normally there is not much movement necessary in any direction to obtain the correct voltage Don t force things if the core breaks you are in trouble In case of a broken core slot remove the core altogether and put it in upside down you have a second try this way The cores are not interchangeable so do one at a time The general alignment can be done as described in the manual with the proper tools and equipment it is a straightforward job For a fully alignment you need a signal generator with attennuator and a range from 0 1 65 Mhz a frequency counter VTVM and if you want to align the noise blanker too you need a noise generator Follow closely the procedure in the manual if the receiver is in a normal condition the changes should be minor Is the set very unsensitive check first the semiconductors in the circuit or there can be resistor or condensor failure that is much more likely than misalignment Closely check for abnormalities burnt or cracked components bad soldering joints bad connectors and other trouble spots If you check carefully use the schematics and the very good circuit description in the handbook to make yourself familiar with the circuits used My experience with 4 of this receivers is that most of the failures I encoun
30. y was working correctly and the problem with the clock was solved also The AM Led was checked and was changed because it seemed at the end of his lifespan It was the first time I saw a burned out Led they seem to have a ethernal life 12 The S Meter was also not functioning properly and after taking it out I saw that the movement was just a block of rust I cleaned it as far as possible but the needle stuck every now and then so I suspected a broken movement or the coil out of his bearings While I had the meter out I searched my junkbox and found a VU meter from an old cassettedeck which was a near perfect fit I checked the resistance of the movement and even that was almost the same I swapped the meter scale and put the meter back The only change was the connection it was reversed on the new meter The FRG 7700 was now working again so I did a tune up according the manual surprisingly it needed not much re alignment Compared with my other FRG 7700 the signals were almost the same strenght so I spended some time to clean the chassis knobs and frontpanel and rebuild the set After rebuilding I will try some modifications to improve selectivity and test some ideas of my own like a clarifier improve sensitivity for the AM bands and others Modifications Fine tuning One of the things I missed on this receivers is a small RIT control or fine tuning a very handy device when I am listening in on a net or
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