Repair Philips PM3384

[ChristophMS72]

Hello everyone!

I'm searching for some help on putting my 4-channel digital scope from Philips back to operation. Some years ago I got it from my former company and I used it sometimes.
Then, one and a half in the past, it began behaving quite strange: it crashed crashed from time to time, and after that it seemed to work no further.

Some days ago I took some time to open the scope to have a closer look to all the electrolytic capacitors for a defective one, but on the first look I did not find any.
When I turned it on, only the fan was working but after a couple of minutes I heard the clicking sound of the relays inside the device and the normal text appeared on the display.

Now it is possible to make measurements with it  but in DSO mode the scope still crashes sometimes. In analog mode that seems to be no bigger problem.
The strange thing about that is a difference between the timebase of DSO and analog mode: both are incorrect (I checked that by measuring the CAL pin @2kHz/600mV) and both also differ from each other.
Does anybody have an idea, what the problem(s) could be?

Cheers, ChristophMS72

[David Hess]

I would start by checking the power supply outputs for voltage and ripple, but chances are the aluminum electrolytic capacitors needs to be replaced.