Electronic – Problematic electronic volume control TC9176P

audiocontrolsignal

I found this site on google while looking for a palce where I could ask electronics questions so bare with me if I'm a bit fuzzy on details and articulation.

I have a vintage sony TA-158 stereo amp with electronic (+/- buttons) volume controls. The volume jumps high and then low and then back to normal within the lower third (1/3) of the volume range whenever I try adjusting the volume.

I purchased the service manual and from looking at the schematics I found there was a Volume Control (signal attenuator??) TC9176P and figured this was the right palce to start. So I ordered a handfull for these ICs and replaced the one in the amp. The problem still persists. From a quick scan of the schematics it looks like the TC9176P talks directly to the main power amp via some basic circuity components (no ICs between them both).

MY QUESTION:
Does anyone have any experience with volume controls / signal attenuators like this and can point me in the right direction as to what component might be causing the jumpy volume. What should I be troubleshooting next?? Dry/faulty Capacitors?? Resistors?? The amp is from the early 1980s so it's around 30+ years old. What components typically give-up at this stage??

Any insights would be greatly appreciated.

Best Answer

The TC9176P doesn't determine what the volume should be - it just sets the volume to what it is told to set it to.

You want to be focusing your attention to the circuitry between the +/- buttons and the TC9176P. This circuitry will be generating a serial bit-stream from some register values which are controlled by the +/- (incremented / decremented).

It sounds like either the data stream is being generated incorrectly or the register values are not being maintained / set properly.

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