AU-9900 Tone/filter switch dropping channel

[KeithD]

When the tone control/filter switch is in the tone defeat/center position or filter position, all is good. But, when I switch to Tone/filter position (to the right) the right channel drops out. I’ve used DeOxit on the switch, but that has not cleared up the issue. If it momentarily push the volume to the max either with speakers or just with speakers set to off, the right channel comes back in the Tone/filter position. It remains for a while, but eventually the problem comes back. I think there was a thread on there some time back with a similar issue, but I can’t seem to find it now. Seems like this really is a dirty switch, but the DeOxit with exercising the switch has made no difference. Any thoughts other that removing the switch and opening it up? That looks like a major pain...

 

[vic]

Try and DeOxit the switch a few times also other switches and some of the circuit boards unplug and deoxit the pins and board itself. I cant remember but there is one small circuit board tucked in a narrow cavity, that was the main problem with mine after cleaning that all was good.
have attached pic of the circuit board.

 

[oldsysop]

When the tone control/filter switch is in the tone defeat/center position or filter position, all is good. But, when I switch to Tone/filter position (to the right) the right channel drops out. I’ve used DeOxit on the switch, but that has not cleared up the issue. If it momentarily push the volume to the max either with speakers or just with speakers set to off, the right channel comes back in the Tone/filter position. It remains for a while, but eventually the problem comes back. I think there was a thread on there some time back with a similar issue, but I can’t seem to find it now. Seems like this really is a dirty switch, but the DeOxit with exercising the switch has made no difference. Any thoughts other that removing the switch and opening it up? That looks like a major pain...

I had exactly the same problem with my AU9900. In my case it was the flat cable with the molex connector. I took it out, cleaned it with isopropyl alcohol and it was solved.

 

[KeithD]

Thanks! I will clean those contacts. Sounds right, it does seem like it is a dirty contact somewhere.

 

[DAnny45acp]

Your right there was a thread with same trouble his midrange potentiometer was damaged.
https://audiokarma.org/forums/index...storation-project.836435/page-3#post-12200189

 

[KeithD]

Your right there was a thread with same trouble his midrange potentiometer was damaged.
https://audiokarma.org/forums/index...storation-project.836435/page-3#post-12200189

Thanks for finding that! I assumed "tone control" would be in the thread title when I did my search.

I think that problem is different from what I had. I could get the right channel to come back just by turning the volume way up momentarily.

I did clean the board contacts as suggested, and the problem has not returned, so that may have solved it. Thanks!

 

[slimecity]

There are many soldered "pass through" connections in this amp - that can cause issues.

If the issue isnt as oldysop points out above, do a search on AK for how to address this.

I also had one of these amps and couldnt locate the source of a preamp channel dropout without investing many hours in the machine - time that I didnt have.

 

[KeithD]

There are many soldered "pass through" connections in this amp - that can cause issues.

If the issue isnt as oldysop points out above, do a search on AK for how to address this.

I also had one of these amps and couldnt locate the source of a preamp channel dropout without investing many hours in the machine - time that I didnt have.

Thanks for the insights. For now, the amp is working just fine. I acquired this recently and it was shipped, so it may be that the connector became loose in shipping, as I had this issue from the start. Eventually I will likely restore this amp, as it seems worth the effort. I have a TU-9900 coming to match the AU-9900.