Sansui AU-9500 Odd Left Channel Problem

Ron13a

Revolver of Vinyl
Hello Sansui lovers. I just scored my second AU-9500. I was foolish enough to let the first one go. I'm determined not to repeat the mistake!

I get it home, hook it up and I get VERY loud trash out of the left channel, static like noise.

I disconnect the left speaker.

The right channel is fine. I adjust the volume and all other pots and switches and there is no static at all. Doesn't look like a quick fix for deoxit. As you can imagine, I was immediately bummed out.

So I tried the left channel with A, B, C and headphones. Nothing but extremely loud static with the volume all the way down.

Next, I pulled the Pre-Out Main-In jumpers out. Hooked my computer into the main in and just used the amplifier section, completely bypassing the pre amp. Slowly turned the volume up on the computer and played a song off iTunes. Both channels are nice and clear.

The issue, I figure, must be in the pre amp section. The amplifier is fine. I put the jumpers back in and hook everything back up and test it. As soon as I hear the relay click, the super loud garbage comes out of the left channel.

Anyone out there have an idea of what's going on here? :confused:
 
You didn't mention which inputs (aux assumed) and if you tried another input (probably sounds the same). Well you've determined that the problem is in the pre. Now a scope would really help. You can send a 1K signal to the left input and then follow the circuit until you get to the spot where there's no longer a nice wave on the screen. I'm no tech - but that's one way to find it. Get a schematic and follow the signal. Even without a scope you can do a visual inspection on the boards for burned resistors and diodes or popped/puffed caps. Chances are it's some transistor though... Good luck! I hope a real tech chimes in with help.
 
I'm not deeply familiar with that unit but the first suspects that come to mind are "known" trouble maker transistors, fusible resistors and capacitors that have suffered "glue rot".

It needs service by a tech.
 
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