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G-7700 Digital Display -not reading proper (FM) frequency

M

Mike Morneau

New Member
Hi Everyone. I have scoured the internet, and these great forums on Audiokarma for some suggestions on the following problem...

The 40pin display IC on the display PCB was replaced recently due to some of the display segments not working.
The problem now is that the digital (vacuum fluorescent) display is not indicating the correct frequency on the FM band. For example, the readout shows ~ 138Mhz at the low part of the FM dial, and will decrease slightly to ~135Mhz at the top end of the FM band. Other than the tuner -which seems a little fussy to obtain a quartz lock, everything else with this receiver works fine. On the AM band, the digital display displays the proper frequency.
I have a hard-to-read copy of the service manual, and am leaning towards replacing the prescaler IC.
Any suggestions would be greatly appreciated.
Thanks in advance.,
-Mike
 
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There have been some recent 'discoveries' of faulty crystals in amongst these display problems. Some having a problem that most thought was that unreliable IC - but when the crystal was replaced all was well. I haven't checked the cost, but the crystal is apparently cheap to buy - might be worth trying?

There are some threads about this issue - and exactly what people did and found out about chasing the faults - let's see if I can find one....

Have a look here:-
http://audiokarma.org/forums/index....n-ic-thread-nudies.640569/page-2#post-8516652

Good luck.
 
Last edited:
Hyperion said:
There have been some recent 'discoveries' of faulty crystals in amongst these display problems. Some having a problem that most thought was that unreliable IC - but when the crystal was replaced all was well. I haven't checked the cost, but the crystal is apparently cheap to buy - might be worth trying?

There are some threads about this issue - and exactly what people did and found out about chasing the faults - let's see if I can find one....

Have a look here:-
http://audiokarma.org/forums/index....n-ic-thread-nudies.640569/page-2#post-8516652

Good luck.
Click to expand...
Thanks John (Hyperion) for the suggestion & link to a much more readable schematic.
I'll report back with my findings.
-Mike
 
Which digital display board do you have in your G-7700? Is it the F-3000 (as most are)? The other bd seems to have the prescaler built in.
 
Well, I did a little test today. I unsoldered the crystal to see what difference it would make. The logic being, if I remove the crystal, there shouldn't be any change to the behaviour of the digital display. There was.... When removed, the frequency display was fixed at 44.7 Mhz and did not change -at all, when the tuning dial was changed from the low end of the FM band to the high end. With the crystal installed, the display reads 138Mhz, and there are slight (10th's of a Mhz) changes when the tuning dial is changed.
I'm guessing that this problem is not likely related to the crystal.
Off to do more troubleshooting...
 
Did the dispaly behave properly and give the correct readout before replacement of the 40 pin IC? (other than missing some segments).
If it did, i would check for bad connections, or possible shorted connection due to the high density 40 pin chip. Or possibly the chip could have been damaged during install.
 
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