Need ideas for repairing soft volume in KORG piano

[hanschee]

Greetings! I’m trying to help repair an electronic KORG SP300 stage piano, which is having very soft internal speaker volume. The slide potentiometer for master volume still affect the volume level from no volume to increasing volume when sliding, but it's still very soft even at the maximum level. The external line and phone out seems to be working fine.

Which component is likely giving the problem?

I’ve already tried swapping out most of the capacitors but the problem is still there.

Could the old slide potentiometer for the master volume be the problem? It does affect the volume level when adjusted, but just couldn’t get the loudness expected. I've difficulty sourcing for this slide potentiometer too, and would appreciate if someone can suggest what equivalent slide potentiometer I can use to replace it.

It's 45mm full length and about 30mm slide distance. .How can I test this potentiometer to see if it is the problem? Can I short its pin somehow to simulate the volume adjustment? (if it's the source of problem at all

 

[hanschee]

I located a data sheet of this sliding dual gang potentiometer and tested it with a meter, confirmed its working properly with 0 to 10K ohm range. So it’s unlikely to be a problem with this component.

Can someone suggest which is the other likely candidates to troubleshoot for the very soft master volume?

The two white wires on back is my desperate attempt to hardwire the phone-out to a small external LM386 amplifier circuit from eBay; to the internal speakers. It failed with too much static sounds and hums, that will be my other option, and I welcome any other alternative solution as long as I get internal loud speaker sound


TIA.

 

[hanschee]

Wishing all a happy new year ahead!

Just a quick update that I’ve managed to repair this piano by swapping out the tiny surface mounted capacitors in the other logic board instead of the big ones in the amplifier board. There were some challenge learning how to remove and solder these smd tiny caps and I panicked when I broke a surface copper thread when forcing one out!

Got the hint from a YouTube video by a guy who repairs pianos. Apparently, volume issues are common for these pianos due to smd capacitors having an average lifetime of 20 years; that’s the age of this piano

Now the it has a new lease of life with full volume! Hope this post will help someone else.