1970's Multivox MX-51 electric piano help

Good Day all,

I have an old Multivox MX-51 that is in beautiful condition.

It has two keys that need repairing. When pressed they play at a hardly noticeable volume compared to the other keys. Not all the way dead but damn close!

It is a pretty basic synth on the inside. So far I have used Deoxit to clean contacts and looked for cold solder joints to reflow. Neither of those helped and all of the soldering inside looks great. This thing is definitely unmolested inside and would prefer to not start pulling parts off without some direction, and even then I may just button it all back up and move on from it so I don’t screw anything else up on it! :laughing:

I’m wondering if it’s maybe bad transistors or capacitors, since the keys still make the slightest noise? They just aren’t being amplified basically.

Each “cluster” for a note only has 1 transistor, 2 capacitors, 6 resistors and 3 diodes

I tried to add pictures but ran into issues.

Thanks for any insights!

The two caps in each cluster are electrolytics. And 50 years old. I would check these first.

I found pics here: https://reverb.com/uk/item/3988692-multivox-mx-51-final-markdown-70-s-wood-black-rare-analog-synth-electric-keyboard

Correct. After swapping out the old capacitors everything worked perfectly.