Channel Issues 9090db

Jereostereo

Active Member
Hello all. I purchased a small trove of vintage gear this week. Everything I bought was super clean and worked perfectly, including six turntables, three pair of AR4x, and several other pieces. The seller also offered a very clean Sansui 9090db for $400. He said he had $280 in work done on it about two years ago to get it up and running, but when he took it home and it didn't fit in his stereo cabinet, he set it aside and never really used it. Bless his heart. I told him I would think about it, and came back the next day with the cash. I tested it with headphones before taking it, but must have fooled myself when I heard a click in both ears plugging them in. Had no real reason to think it was defective. Anyway, I get it home and only one channel is working.
I did enough trouble shooting to determine that it is the left side of the power section that is out. Both pre out sides work when fed into the right power section, but neither in the left. From previous posts it was recommended to really REALLY clean all switches, which I have done to no change. I also checked the fuses and they seem fine. I have the top and bottom off and have sprayed deoxit everywhere.
So my only real question is regarding the protection light. When I power on, the red light flashes about three seconds, goes dark, and there is no green light. I think from researching other posts maybe there should be a constant green? Would this offer any clue regarding the problem?
Thanks in advance to everyone.
 
If you have sound from either channel it is not in protection. There is a resistor in the circuit for the green led that has been known to fail and when that happens you get the red led acting normally (flashing) but no green led when it comes out of protection.

In most cases when you have this kind of channel drop, it's nothing more than dirty controls. When you say "sprayed deoxit everywhere," it does no good at all unless you get it INSIDE each of the pots and switches. To get access you need to do more disassembly than just taking the covers off. To get to the dolby switches, you need to remove the whole tuner tray.

Look at the back of the unit. Are both U shaped jumpers in place? They connect the preamp to the amp. Next, "exercise" all the controls. Vigorously move them all back and forth or in and out. Any change in the dead channel when you move a particular control? You may get lucky and fix it by doing this.

Please post the serial number for the database. Click on the link in my signature block.

- Pete
 
Thank you LB. I thought it possible that the lack of a green light was just a failure. Good to know. When I said I had sprayed everywhere, I meant all the usual places. Very specifically the monitor switches and other spots along he signal path. Tried to reach beneath the Dolby board as best I could - not very motivated to do any disassembly. Unless, however, the Dolby section is the likely culprit. I cannot get so much as a slight click or pop out of the dead channel by jiggling every switch and button on the unit. Might be one for the tech. Cheers.
 
Having issues with 1 channel, and no green light can also point to a dirty speaker protect relay. Remove the bottom cover, and with the unit on, tap the speaker protect relay with the plastic end of a screwdriver. Its best to do this with headphones, so you can listen. If you hear popping with sound coming and going, the contacts are dirty. You may also notice the green light coming on when you tap because one of the contacts support the protection led. De-energized a normally closed contact provides the flashing red. When the contact closes, the normally open contact closes and the Green light appears.
 
Also take some time cleaning the balance control which may cure the problem. Here's another possible solution which is not for the squeamish. I had some Wurlitzer organ speakers hooked up when the left channel went dead a few months after cleaning. I was so upset that I turned the volume almost up to max as I was so mad that I didn't care if the speakers blew. Lo and behold, the left channel came to life (scared the crap out of me!) and I turned the volume down quickly. The left channel continued to play and has been playing perfectly for the last couple of months. BTW, the speakers didn't blow. I still don't know why the channel came to life, but I'm glad it did considering how much time I spent in the restoration!
 
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