Fredenstein V. A. S. Microphone Preamp

I bought this unit more than a year ago and I let it sit for most of that time as I was able to use other mic preamplifiers. A few weeks ago I pressed into service as an audiophile told me that he really loved his unit. Updated (Oct 1, 2024)images. Please check the 2 additional photos. One shows the item with the -20 dB pad engaged (you can tell by the LEDs of the Level meter) and one without. I had a condenser mic that required +48V phantom power plugged into the XLR IN on the back of the pre.

When using this (I have a condenser mic), I noticed that it produces a "scratching" sound, causing really bad distortion which is unpleasant. I decided to open up the unit, to see whether there were any loose wires, but didn't detect any. Then I thought I would very gingerly apply DeOxit to the "Gain" and "Output" knobs(pots) as I thought that the contact surfaces inside the pots might have gotten oxidized after the unit was just sitting on my desk. The problem can't be the XLR and TRS cables that I used (both made by Mogami).

Perhaps the issue is temperature related (thermal issue). See the several pictures that I have provided. The unit appears to work well - when the scratching sound doesn't appear - but the cause of the glitch is still unclear. It could be that the unit works for a day without the glitch. It is hit or miss. Someone who is willing to spend a little time with the unit will likely be able to get it all sorted out. I just don't have the time to devote to any more trouble-shooting.