Korg Maxi-Korg 800DV / Univox K3 part 6: Controls clean up

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With the keyboard all cleaned up, the circuit boards capacitors replaced and much general clean up attended to, I turned my attention to the controls – the sliders, pots and switches that you interface with to play the instrument. The Traveler sliders in the VCF section felt awful when I first checked out this synth. They were stiff and notchy when they would move. I figured worst case I would have to find suitable replacements for the 4 of them. I don’t remember if I even tried any of the other controls – once I got bad news I just moved on.

Starting at the end. The controls have all been cleaned and it’s nearly ready for final assembly at this point.
I took this picture to help me wire it up if I got distracted and couldn’t remember what went where.
I desoldered and removed a slider to open it up and see what needed doing. Here I am using my lead snips to gently pry the metal fingers that hold these together. Once all 6 are bent out of the way it falls apart.
It’s hard to tell, but there are two thin pieces inside the slider at the top. the black one is a dust seal and under it is a copper plate to give the slider a nice feel. I was worried about removing the seal in case it also acted as an insulator, but I see no electrical connections to the copper piece through the slider contact, so I am pretty sure it isn’t an insulator. This all got cleaned out with q tips and reassembled.
No wonder these didn’t work very well! Feels much better with the dust seal removed and all cleaned out. Rather than desolder and remove the other three I disassembled the bottoms from the tops leaving the metal bodies in place – much quicker.
These were all nice and smooth feeling although slightly stiff, so I wiped them off, squirted a shot of fader lube in each and exercised them a bit.
There were 4 tantalum capacitors on these switch backs – I replaced them with electrolytics I had on hand.
This pot is the coarse tune for the lower synth. It is frozen. I tried penetrating oil and heat to no improvement.
Here I am using a little brute force. I gave up and ordered a new 1K Linear taper pot from Mouser. Actually ordered two so that if they are noticeable different feeling I can replace both.

So where does this leave me?

  • I still need to refinish the wood cheeks to use the originals until I can get new made
  • I need to clean up and remove some paint speckles around the bodywork from someone painting with a roller near this – hopefully it is latex paint
  • I have 1 capacitor to replace on an oscillator board
  • I have to repair the foot that got bent in transit
  • I need to power on and test it – all sorts of things can go wrong there.

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