GumiElectronic

Have a bad volume slider on your TR-707? Don’t go looking for a replacement slider (yet). If you’re lucky, it can be a very simple fix:

My TR-707 had a broken slide pot for the Mid Tom. It wouldn’t change the tom’s volume and the voice was very loud and a little distorted from both the main and individual outputs. When I tested the pot with my meter, I got a sporadic reading of several hundred k anywhere in the slider’s travel. When I removed the pot from the board, I noticed that the slider’s shaft was a little loose in its track (i.e. I could wiggle it up and down slightly).  Then I noticed I could get the normal resistance range (0R to about 40k) if I pressed down on the slider’s shaft while moving it. To fix the problem, all I had to do was lightly pinch the tabs of the slider’s case, which reseated the slider snug into its track. Now it works like new. Here’s a quick how to:

1) Remove the offending slide pot from the PCB.

2) Test the resistance with a meter, sliding the shaft as you normally would. If you get seemingly random readings, this might mean the shaft is loose in its track.

3) Try pressing downward on the slider’s shaft while moving it and test the resistance range. It should go from 0R to around 40k (or at least that’s the range of all the sliders I tested on my 707). If so, this fix will probably work for you. If not, the problem might be someplace else, though you can try cleaning the contacts with DeoxIT, which might help.

4) Look at the rear of the slider’s case and note the four tabs holding it together (marked in orange below):

5) Lightly pinch these tabs into the case using a needle-nose pliers or similar tool. Be careful not to pinch too hard. If you do the slider can become stiff/sticky at the top and bottom of its travel. If that happens you can just pry the tabs outward again and start over. You can try just pinching each tab a little at time until you get smooth action and solid resistance readings:

6) It wouldn’t hurt to clean the slider with DeoxIT as long as you’re here, eh?

7) Once the slider is tested and functioning normally, solder it back into the PCB. That’s it.