Sansui 9090 Driver Board r

I've got a DBT but thought that the variac would allow the fused resistors to build up without blowing them. Will they not blow with the DBT?
 
It's hard to say if either a Variac or DBT will prevent old fuse resistors from blowing. They become unstable over time. The DBT will lower input voltage as well as limiting current draw. Unless your Variac has an ammeter, you have know way to know if the unit is drawing too much current. Even if it has an ammeter, you have to be looking right at it. The DBT gives a visual reference that you can see from another room. Much harder to miss the que.

- Pete
 
I wanted to publicly thanks Robisme for making this happen. When I posted originally looking for someone to redo the board, Rob reached out and offered to do the job for me. I sent him the board and it was quickly returned, all parts needing replaced properly, and it is the reason this vintage Sui is breathing life again. Rob, a HUGE THANK YOU for your kindness, generosity, and for helping a total AK stranger. Good karma will come back to you in spades my friend.

You're welcome, glad to help.

I recommend you check the DC offset and bias.

Rob
 
You're welcome, glad to help.

I recommend you check the DC offset and bias.

Rob
Thanks Rob, that's definitely on the list. I have not done either before so need to research it a bit. If I ever get done with work, maybe can do it this holiday week.
 
DC Offset with meter set at 200mv and leads securely in the speaker wire spring clips on the rear. Receiver warmed up for 15 minutes, all set flat, volume zero in Aux position. Turning speaker selector to Off I get a zero reading.

Setting speaker selector to A, B, and C and testing all 6 pairs of wire connections are all pretty much the same - I'm reading pretty steady 42-44 on the Left channel. Right will come in at nearly dead zero or .1, then starts moving all over the place bouncing around eratically from 20ish to 50ish or a high of 60. It won't settle in and get a good reading.

Would the fact that I've not cleaned any of the pots yet make a difference? I have scratchiness in the volume pot and it needs to be cleaned. Should I expect the right channel to settle in with a decent reading after cleaning?

Setting bias looks a bit more complicated at a glance so far:)

I can certainly post this elsewhere or if the topic has already been covered, just let know, thanks
 
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Removed the bottom case again and Deoxit cleaned all the toggles and rotary switches on the bottom row. I did not pull the face plate so could not access the push buttons in the row above. Good news is this cleaning removed all the static and it's working great now!

Retested DC offset and the right channel is now getting stable readings, however, they are high numbers ranging from low to mid 80's to low to mid 90's. The left channel reads steady and consistent at 36-38, much better and seemingly acceptable levels. I should probably let the unit play for few hours as its been in closet for 20 years before being woken up here again. Maybe caps will set in and I can try the readings again.

I will take a shot at adjusting the pots for the offset next.

Bias looks complicated unless I'm missing the boat on how to with the 9090, the pots are very sensitive to the slightest movement and that could make it worse. Again, not my intent to make things worse being a rookie on this stuff!

Thanks in advance for any advice AK gurus!
 
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Definitely try to get the DC adjusted down. As for the bias, if it's not running hot at low volume after 15 minutes, and there is no distortion at very low levels, then you are probably good.

Rob
 
Thanks Rob, I just read an awesome post here and reset the DC and idle current on my Pioneer SX980. I am tacking this one next!
 
DC offset all set. .1 on right channel and less than 1 on left channel. Right is rock steady at .1 and left fluctuates a little but both are great, thanks again!

I think after readying about bias, will leave it alone and use the receiver awhile. It doesn't run hot at all with the little I've used it so far. Thanks again all! IMG_7113.JPG
 
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