I acquired this scope from work probably 30 years ago. We had purchased several of them for monitoring purposes during production testing of amplifiers. This one had a high frequency interference or oscillation on the channel 1 input. I recently pulled it out of my closet to see what it needed for repair.
At first I was suspicious of something wonky with the time-base and I devoted a some time to making sure all of the wave forms looked right. Next I traced the input and found the interference was coming from the -12 volt supply rail. Everything was fine before the -12v regulator but showed a high frequency oscillation after.
I decided to tack on two 100uf capacitors in addition to the bypass capacitors that were there. They showed 15uf on the schematic but in reality they were 33uf Phillips caps.
.
Well, that was it. Once again I found capacitors that were being baked by heat. These ones are situated between the voltage regulators on the power supply board and overtime were cooked by the regulator heat. When I measured them they measured in the low pf range so they were effectively open.
Removing the power supply circuit board is not that difficult once you have the rear panel separated from the rest of the unit. I left the CRT attached until I had the rear portion removed. The biggest hastle was the power switch. In the end I unsoldeed the switch so I could leave it and the powercord inplace. I then removed the bare wires attaching the switch to the power supply board and replaced them with insulated wires that I attached to stand off's I installed on the topside of the board.
Oh, and while you're at it there is a rifa capacitor across the line that should definatly be replaced if it hasn't already self destructed.
Well, that turned out to be a pretty easy fix in the end. It's a scope that I wanted to have more or less permanently attached to my B&K curve tracer on the bench. It seems to fit that application pretty well.
Phillips PM3207 Operators Manual
crwdns2944067:00crwdne2944067:0