As some of you know, I also have been rebuilding a 9090db over the last few months. Not much time these days....

Anyway, I am down to bias. The driver board is re-capped, and resistors are all changed. I did change out the VD1212 diodes as recomended btw. Bias on the right channel holds steady at 30ma +/-5 microamp.

Bias on the left channel fluctuates about 4ma +/- from 30. Seems a lot. It also starts high, at 120ma cold and quickly settles down in about a minute.

Any ideas where to look for this one? I'm not a good amp tech, so could use a little advice there. The receiver otherwise runs cold to the touch on the heatsink even after a day running low volume. DC offset is pretty much as close to zero as you could want on both channels.

Thanks..

The trim pots are dirty. clean them with deoxit or replace them. Take an ohm reading from each one and note it before cleaning or replacing. Also, allow about an hour to warm up before you make final adjustments.

Cleaned the pots and blew them dry. Same thing. I was hoping to avoid it, but I'll order some pots anyway. It just never ENDS...:cry:

OK.... pots replaced.

Power up, relay clicks and bias on right channel runs almost immediately around 30ma and very stable.

Bias on left channel starts about 50ma and slooowly drifts down to about 30ma +/- a milliamp. Better, but not as stable as the right.

The question is: Why is the left channel starting high and drifting down plus a little unstable and the right is by all account rock steady?

Which parts would be the most likely culprit? Once again, amplifiers are foreign to me. Ask me about video monitors instead.

And.... should I worry about it? It's been playing hours on end just fine, does not get warm unless I want the police to show up.

I've just had so much trouble with this one, I'm a bit paranoid now.

What does the bias do with a load on it? I think it's normal for the bias to climb to a higher level untill it warms up. They have temp-comp diodes or the like, on top of the drivers that kinda work like an O2 sensor in a car. They keep the car running when it's cold. Make sense? I would'nt worry about it. Also, replace the red-dot diodes at the bottom of the board (VD1212). Use a series pair of 1N4148 diodes to replace each one.

Also, replace the red-dot diodes at the bottom of the board (VD1212). Use a series pair of 1N4148 diodes to replace each one.

First thing I did. :thmbsp:

My guess is that it's fine, one side is just not AS stable as the other. But I had so much grief with this beast that I start to sweat at every little thing.

It sure does sound VERY good, though.

Well, it's still not quite fixed.:gigglemad

I know some of you love these sansui receivers, but it is by far the WORST piece of gear I ever had. I don't know why I spend so much time on this pile.

It would be one thing if it had only one problem, but no.... it had many.

Anyway, the 9090db plays wonderful at low to medium volume, but the left channel (the one with unstable bias) starts to click or clip at about 10-20 watt on the meters. This did get better as the bias was properly adjusted, so it does it at higher volumes. :scratch2: Before it would "CLICK" very hard at lower volume. I thought I finally had it... but no.

Once again, I am not in my element when it comes to amplifiers. Rebuilding the bad volume pot, the tuner can, the tuner power supply, the dolby board, aaaand the driver board wasn't difficult. But now I suspect that maybe I do have a flaky output?

I suppose I could either swap the outputs around as a test or turn the driver board and see if the problems follow. I KNOW it's something really stupid, but I seem to be too close to see it.

WHERE ARE THE EXPERTS!!!????


I just thought of something.... it has all it's original outputs. Would it be a good idea to just replace them? I am on a wild goose chase here, maybe it IS the outputs?

Well, it's still not quite fixed.:gigglemad

I know some of you love these sansui receivers, but it is by far the WORST piece of gear I ever had. I don't know why I spend so much time on this pile.

It would be one thing if it had only one problem, but no.... it had many.

Anyway, the 9090db plays wonderful at low to medium volume, but the left channel (the one with unstable bias) starts to click or clip at about 10-20 watt on the meters. This did get better as the bias was properly adjusted, so it does it at higher volumes. :scratch2: Before it would "CLICK" very hard at lower volume. I thought I finally had it... but no.

Once again, I am not in my element when it comes to amplifiers. Rebuilding the bad volume pot, the tuner can, the tuner power supply, the dolby board, aaaand the driver board wasn't difficult. But now I suspect that maybe I do have a flaky output?

I suppose I could either swap the outputs around as a test or turn the driver board and see if the problems follow. I KNOW it's something really stupid, but I seem to be too close to see it.

WHERE ARE THE EXPERTS!!!????


I just thought of something.... it has all it's original outputs. Would it be a good idea to just replace them? I am on a wild goose chase here, maybe it IS the outputs?

Sorry to hear the frustration in your post...
You could swap the outputs around, they simply unplug from the heatsink, changing them is not a good choice, I think originals are unobtainable, any you find are likely counterfeit.Did you test them all with your meter?
Is it time to send this along to say CDFixer? I think he's been said to be quite good at these X0X0 units?
Casey