Hot Rodding a Harman/Kardon T20, update 1.

A quick update about this build. I document my work if anyone else run into a similar problem. Cleaning the motor being enough to fix the erratic motor control was a bit of wishful thinking. It was spinning along fine for about three full albums. The speed then started to fluctuate a bit. Not per revolution and not much but enough for me to know that I had to tear it apart again.

Looking through the schematics and there is not much and not much in the service manual either. It could of course be something off with the motor still or almost any other component. But I consider the two trimpots and all electrolytes being obvious suspects. So I started with the trimpots, using some contact spray on a 2000 grit paper to get rid of any oxidation on the wipers.

The whole trimpots then got a full cleanup before I went on to the electrolytes. There are only four of them on the control board that is attached directly to the motor. I don't know if the values can be read from the image below but the stock values according to the schematics are; 4.7uF/25V, 3.3uF/25V, 10uF/16V, 0.47uF/50V. That was not exactly what was on my board but I replaced them with what I got in the bin (somewhat of an upgrade compared to the stock items).

The fifth capacitor (330uF/16V) is located on the board with the transformer. I replaced it too off course.

I also took the opportunity to recalibrate the trimpots. This is a bit tricky since the trimpots can only be accessed from underneath with the bottom plate removed. But it is nice when it is finally done and it is spinning exactly at both 33 and 45 rpm with the speed control in neutral.

It might be a bit premature to make a victory lap but it now seems to work flawlessly after more than three albums. Right now enjoying Fleetwood Macs Tango in the Night while holding my thumbs...