I recently took my 9090DB out of 5 years of storage and it immediately went into power protection mode. After reading several excellent posts on the subject in this forum I decided to attempt to troubleshoot and repair the problem(s). I found several bad resistors on the driver board and one on the power supply board. I also decided to recap the power supply and driver boards while I was at it. I also used Deoxit several times on the switches and controls. After the rework I set the bias and DC offset per the service manual and fired up the beast. It came out of power protection but there is distortion in the right channel. The left channel sounds fine. I believe that the problem is in the amplifier section because I removed the preamp-to-main jumpers and fed the mains with my Hafler preamp and the distortion was still present. I have also reversed the driver board and the distortion stays in the right channel. I have tested the output transistors and the transistors on the power supply board and all test OK. Any ideas as to what may possibly be wrong?

Bad output relay, bad speaker selector switch, or bad output transistors.

EchoWars,
Thanks for the quick reponse. I will clean the speaker selector switch again and see if it helps. If the transistors are the problem I am assuming that switching them from left to right should switch the distortion to the other channel. Do you know the orientation of the output transistors on the back of the unit as they relate to left and right channels? Is it as simple as swapping the four on the left with the four on the right?

That issue rises to the level of importance only if it fixes the problem or makes it worse. :D

..but yes, I'm fairly certain that's the deal.

Swapping them one at a time will help isolate the bad one.

- Pete

I have cleaned the speaker selector switch twice with Deoxit and tried all 3 speaker positions with no change. I then switched the output transistors from left to right and top to bottom and distortion stays in the right channel (no change from original problem). During testing I noticed that the power level meters are at the same level for both channels when the speakers are turned off. As soon as the spekers are turned on, the right channel reads much lower than the left. Does this additional power level info help narrow down the problem? Also, how do I test for a bad output relay?

You can bypass the protection relay with jumpers to test it. I'm not sure what to tell you about the meters. Are they reading above zero when the volumn is set to zero?

- Pete

They read zero when the volume is set to zero.

Does bypassing the protection relay change anything?

- Pete

This problem can be caused by a bad feedback circuit on the driver board. I have seen this numerous times. Everything looks normal (using a scope to monitor the input to the protection relay) until the relay clicks in then there is distortion, every time it has been a resistor or transistor on the driver board that caused the problem.

Hard to troubleshoot without seeing the unit.

Check the following and note differences in the values from the right and left channels
Note the odd numbered components are in the left channel, the even in the right.
I have paired them for you

D7-D8
D9-D10
D11-D12
R55-R56
R57-R58
TR15-TR16
TR17-TR18
D13-D14
D15-D16
R63-R64
R65-R66
R59-R60
TR3-TR4

Good Luck

Welcome to AK, elGuapo:thmbsp: Aren't the folks here cool?:yes:

I too, have a 9090DB that needs repair. I bought mine in Germany in 1976, but have not been able to use for several years.
Mine has a problem with one of the channels also. I can't remember which one, right I think. The Dolby doesn't seem to work properly either. The tuner string is also broken; I think it needs a major overhaul.
I really want to get it repaired; I haven't been able to afford anything comparable; guess I don't really want anything since I have this, just need to get it fixed.
Any idea where I can take it? I live an hour east of St. Louis. I haven't been able to find anyone here that works on them. Can you help?

Thanks,

tgraves2

Tgraves2, welcome to AudioKarma. The 9090DB is well worth fixing. Contact AK member EchoWars. He's a wizard with this stuff working out of Lees Summit MO.

- Pete

Checked all the suggested components on the driver board and all test OK. Also, in my original post I did reverse the driver board and the problem did not change to the other channel. It makes me think that the driver board may not be the problem. Thanks for all the suggestions.

tgraves,
I don't know that I've heard of anyone here in your area either.... the actual closest person here to you I'm aware of would be Nakdoc (I think that's how he spells it), he's in Nashville. Other than that there's a bunch further east and points south.

Ron

Problem Solved!
As it turns out, AK'er APPROSE lives about 20 miles from me and kindly offered to invite me and my receiver to his house for a troubleshooting session. We narrowed it down to a problem on the power supply board and he found that one of the fuses was not making good contact in it's holder. After crimping the tabs on the fuse holder to make the fuse fit tightly, no more distortion. The unit is now at home driving my Polk Audio 10A's and has never sounded better. In fact, I don't recall it ever sounding as open with this much detail and I have owned it since it was new. Don't know if the perceived improvement is from the recapping or not. but I would like to think so. Many thanks to Ron for taking the time to help me out. He is a real expert on this stuff and a super nice guy. Also, thanks to everyone else who provided help and suggestions.

Another AK and [Exclusively Sansui] success story! :banana:

Is this place awesome or what? :tresbon:

Paul