Pioneer SA-500 Restoration Help Bad CH2

[misterc57]

forgot to mention that the old VR4 had very high resistance readings, in the K ohms.

and it looks like there is some kind of white substance or glue. I will see if I can force it to turn and if a cleaning can bring it back to operattion.

edit: I was able to scrape away the white stuff and rotate and clean the pot. It reads over 1M resistance so it is a goner.

[Helmholtz]

VR4 should be a 100R trimpot. Try to find a similar size/footprint. Wattage rating is not critical.
If the idle current is too low there will be crossover distortion.

[misterc57]

VR4 should be a 100R trimpot. Try to find a similar size/footprint. Wattage rating is not critical.
If the idle current is too low there will be crossover distortion.

So far no luck sourcing a 100R trim pot with 2 legs. Anyone know some sources? Do I have to use a 3 leg pot?

The old pot has a 10 mm spacing between the two legs.

Thank you

[The Dude]

I'd just clip one leg off a regular pot. Look for a trimmer with approximately 10mm spacing between the center and one outside leg. It should be easier to find.

[misterc57]

Not many 100 ohm pots out there. I found a trimmer. see pic.

The outside legs are 10 mm apart.

I am thinking that I can jump one outside leg and center leg. Then insert the outer legs to the board. Make sense (will this work)?

[The Dude]

That should work just fine as you described.

[misterc57]

Finally got the new trim pot installed. Amp can be insanely loud for its size.

Adjusted to @ 13 mV voltage across the emitter resistors of the outputs (R31,32,33,34). Need to lookup if this is a proper value. It was the lowest I could get them to be matching.

[misterc57]

I had to replace both trim pots to get both sides around 5 mV across the emitter resistors of the outputs (R31,32,33,34)