Repairing power supply unit of Philips PM 3065 CRO

[afsar]

Hi everyone,
I want to repair power supply unit of Philips PM 3065CRO of the late 80s. That is my first repair. Please suggest me tips and safety issues. Can multimeter be sufficient to test and repair power supply unit as it has HT voltage? Please help!

[jancumps]

my bet is that the largest electrolytical capacitor failed and took out the rectifier. a typical failure these days for 80s and 90s Philips scopes.

[cheeseit]

You should have kept this in the previous thread you started but maybe a mod can merge them.

I'd suggest that you just replace most capacitors without measuring anything, especially while the scope is powered up, but only attempt this repair if you honestly feel confident that you can do this safely. This kind of repair can easily kill you - keep that in mind at all times. Otherwise get someone capable of doing it to help you, or pay someone to do it. Remember that both the CRT tube and components on the PSU board can kill, and not just by electrocution. Your life is worth a heck of a lot more than a scope repair, and being dead just sucks.

Read this and this, and make sure you understand everything before you proceed. Perform further research (Google) if you're the least unsure, or just stop here. If you feel up to it then discharge the CRT safely.

Follow the disassembly procedure in the service manual (wait ~30 seconds for the "...Processing..." to change to a "Get Manual" download link), making sure only to touch the board by the edges and discharge the capacitors safely, especially the two large ones behind the power switch. Perform further research (Google) if you're the least unsure.

The reason I suggested checking and replacing electrolytic capacitors in your original thread is that the whistling/whine is most likely caused by the transformer being strained by bad/out of spec caps. This is apparently a common problem on this series of scopes, and I repaired a similar scope with the same problem recently. I replaced all electrolytics except for C6007, C6008, C6100 and C6101 that were fine. Almost all the smaller ones were way out of spec and I'd suggest that you start by replacing those first.
Keep in mind that several versions of this PSU were used but they are generally more or less like the one in the SM linked above. Replace caps with same voltage rating and capacity, preferably 105° degree, and don't use super low ESR types. You should also replace the golden resin encased RIFA caps if found since they have a strong tendency to blow up.

You didn't specify if the scope works, apart from the noise, so this may or may not be all that you need to do to repair it but it's certainly a good start.