Sansui 881 - Offset is OK but speakers are popping ... and smoke!

GJB

New Member
Hi guys. First post/question because I have managed to find answers to all previous questions from earlier posts. With your help, I have restored/recapped a Marantz 2235B and a Sansui 6060 that have been needing attention for years. So thank you very much for making this hobby so fun and rewarding!

I recapped all the Sansui 881 boards except the AM/FM sections. I changed the four output transistors to MJ21194Gs; the originals tested OK but I wanted new (so maybe this is my problem). Bias is set according to the manual. DC offset is also set according to the manual, and on the low side - around -8mV.

The issue is that I get speaker pops and SMOKE from board F-2436 on startup when speakers are attached.

The unit sounds great and I haven't found any other problems. Any advice would be greatly appreciated. Thank you
 
Pops, smokes, sounds great, just don't belong in the same sentence unless you're talking about a fireworks display.
 
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Yes I agree with bbqjoe. Pops and Smoke are signs of serious problems, and while you may momentarily have sound, it will stop as the components on the driver borad burn or fail. Use a dim bulb tester as you troubleshoot. Make sure the mica insulators are in place for the outputs, make sure proper NPN and PNP were done, although is they were reversed, you probably wouldn't get any sound. You may want to put original outputs back, especially if you bought the replacements on ebay. I only trust replacement outputs from places like mouser, and parts express. Too many counterfeits on ebay
 
This is not good - do you know which side its on. The new MJ21194G's, will only fit one way, and if you had a breached mica, you'd blow fuses instantly. Since you haven't replaced any transistors (recap only I assume ?) - you should start by meticulously checking each cap on the shared driver board F-2436. Check polarity, and especially the new solder joints on the backside - that one is not touching a neighbor trace when not supposed to. If you know which side is bad/good, then you can compared sides as it can be confusing at times to determine when the traces/joints are supposed to touch and when you need separation - the continuity function on DMM is a quick tool for that. Good luck !
 
Thanks. Insulators are in place and I got the parts from Mouser. I put back the original output transistors. No change. I will go back and check all caps polarity and solder joints and compare side to side. The problem side is clear.
Thanks again - very quick responses!!
 
It could be a DC filter cap on the driver board reversed. The screen printing on Sansui boards is many time wrong. Verify polarity by looking at and matching to the schematic, as well as verify via DC volts acrodd the cap. (the more positive DC voltage side always goes to the + pin) So that means that with a negative power supply, the + pin usually goes to ground, and the negative pin has neqative DC volts
 
Appreciate the replys. The smoke was coming from R46 on the F-2436 board. I pulled it and it tested ok (150 ohm) per spec; replaced it anyway. One solder joint on a cap was loose b/c of delaminated trace; I fixed that and no more smoke. But I still have speaker popping on startup from both speakers. The DC offset is now too high on the left channel, around 45mv. I'll search around for threads on this and come back if I need more help.

Thanks!!
 
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