Optimus STA-20 ... Left channel intermittent

[knoxl]

Hi,

I just picked up an Optimus STA-20 for $15 at a swap meet. It's a decent office radio with all the power I need for a small room. My problem is that the left channel seems to drop out sometimes. Oddly, if I push the Volume knob in the left speaker starts working again. If I release it then sometimes to left channel continues to work and sometimes it doesn't.

How would I begin to troubleshoot something like this? I done a little soldering in my life on disk drive PCBs but have never worked with radio equipment before. Any ideas? Any direction would be helpful. Thank you!

I've been looking for the schematics on this mini-black STA-20 but I can only find the 16 page user manual.

 

[prcguy]

The center wiper of a potentiometer is spring loaded to keep the contact riding on the carbon or conductive plastic resistor surface. It could be the spring has failed or the volume control was hit, pushing in and bending the contact. You can sometimes take them apart and do mechanical repairs and sometimes not.

You could also try carefully spraying a cleaner/lubricant into the volume control and the best thing on the market for that is Caig Labs DeoxIT D5 contact cleaner.

 

[W1KNE]

I agree with pcrguy, the volume pot is faulty. It's possible one of the solder joins the pot has become broken and just needs to be re-tacked.
The more likely culprit is, there is gunk in the control itself and it's causing the bad connection inside the pot like he said. Those are usually stereo pots, and are common parts you can find at digikey.