This is the 2nd Sansui 9090db I have had on the bench in the last 6 months, as well as a complete rebuild of a G-9700 in between. This 9090db is very strange. After complete cleaning and deox i powered it up on Variac and was thrilled to see it come out of protection mode right away! I have power to the PA and of course the output transistors. But no signal past the Dolby board. I have recapped the Dolby board since I had it out already. Repaired all of the pull through circuitsI The ribbon cable needed replacement after only a few days of working in that area several traces failed. I have replaced with some very sturdy new ribbon cable and reasembled. Still no signal. Using scope the farthest I was able to trace signal was Pin 2 of the BA 312 IC on the Tone control board F-2544. Now I can's see it past the the F-2654 Push Switch. Odd about that PCB as well, the traces were physically broken on the Tape Monitor 1 switch, almost like it was done on purpose. I thought that would be the problem but it wasn't! I am stumped. does anyone have any ideas? Going to start checking voltages on the boards.
SANSUI 9090db Losing Signal at Push Switch PCB F-2654
- Thread starter HankM
- Start date
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- Tags
- 9090db dolby board sansui
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Here are my thoughts. I really dislike those dolby/switch board pairs, which can be very confusing especially seeing there are 2 different flavors. Much of the damage occurs to the ribbon cable when attempts are made to pull out the pair of boards. I found the best is to unsolder the ribbons from the dolby board before attempting to remove either board. But I am hoping your repairs of the dolby board didn't create any issues. Verify especially that the wires connecting the dolby board to the volume/balance circuit board are all in place, and that the molex connector is in place on top of the switch board, although I think that would only affect am/fm. And make sure the pre out main in jumpers are in place.
In those Sansui's basically all of the functions and various switches feed into the Dolby/switch board pair. The output of this feeds to the volume/balance control board. the output of the volume/balance board feeds the Tone board which outputs to the Pre out connections. If you have audio on pin 2 of the BA312 IC, this means audio has made it though all the switches, dolby board, vol and blance control.
You should find audio on pin 6 of those tone control BA312 IC's, and hopefully audio at the pre out connector to main in connector jumpers.
If no audio on pin 6 of the BA312 IC but you have audio on pin 2 still, check your 29vDC supply feeding the tone board, or look for a leaky or shorted filter cap (C602) on the tone board.
In those Sansui's basically all of the functions and various switches feed into the Dolby/switch board pair. The output of this feeds to the volume/balance control board. the output of the volume/balance board feeds the Tone board which outputs to the Pre out connections. If you have audio on pin 2 of the BA312 IC, this means audio has made it though all the switches, dolby board, vol and blance control.
You should find audio on pin 6 of those tone control BA312 IC's, and hopefully audio at the pre out connector to main in connector jumpers.
If no audio on pin 6 of the BA312 IC but you have audio on pin 2 still, check your 29vDC supply feeding the tone board, or look for a leaky or shorted filter cap (C602) on the tone board.
Somewhere in the AK archives there is a very detailed thread posted by I believe either CdFixer or CdFac that accurately details the entire dolby board signal path. Could not find it, seems to me LBPete was working on one when the subject came up many years back, perhaps he will chime in on where that thread my reside.
-Lee
-Lee