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C33 - no sound (?)

R

R&B Stereo

New Member
Greetings y'all!

I have two units in the shop for servicing from a client, a MC2155 and a C33. The client said that the combo suddenly had no more sound (while playing). The 2155 did have some caps that were shot (power supply board) but didn't appear to cause a major issue with it. Anyway, it has been recapped, etc... and is playing fine. But the C33.... 'dead' - no sound output. It turns on fine, not shorts reported on the DBT, and relay clicks. Wondering if any of you out there could share a hint where to look first?

Much appreciated, as always.

Brian
 
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The schematics available for the c33 suck, but with the block diagram from the owners manual it should be pretty easy to trace the signal.

The last c33 I looked at had a faulty 5534 on the loudness/compandor board.
 
jlovda said:
You seem to be in the business of repairing equipment. Did you do any signal tracing or check voltages?
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Fair enough, jlovda ;-) I do run a side business of restoring / repairing vintage solid state stereo. For quite a few years now, and hundreds of units under my belt.... I am not an electronic engineer but got trained by one and self-taught otherwise. Mostly work on weekends. I finished working on the MC2155 yesterday Sunday late afternoon and was time to get the C33 on the bench. I was wrapping up my day and didn't want to start the signal tracing. Without probably getting back to it before next weekend, I thought I would request here if any insight from some that may have encountered the same, just to potentially save some time. That's all :-)
 
As stated, muting transistors or the switching FET transistors can cause no audio, (I’ve replaced both in a few units) but both channels simultaneously makes that unlikely. Sounds more like PS.
 
Good evening y'all. I thought I would report back that the C33 is singing again. I traced the signal almost all the way to the pre-output... ended at the optocouplers. I had concurrently come across some other post with someone having trouble with the CLM6500 optocouplers.... turns out they were indeed shot on both channels! replaced them with compatible replacement and problem solved! Thanks all for your support.
 
We
R&B Stereo said:
Good evening y'all. I thought I would report back that the C33 is singing again. I traced the signal almost all the way to the pre-output... ended at the optocouplers. I had concurrently come across some other post with someone having trouble with the CLM6500 optocouplers.... turns out they were indeed shot on both channels! replaced them with compatible replacement and problem solved! Thanks all for your support.
Click to expand...
What did you replace them with?
 
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