Kikusui COR5541U oscilloscope readout off screen

[JanR]

Hello!

I've been following Eevblog for quite some time and now I finally joined the forum!

I recently bought a Kikusui COR5541U analog/digital oscilloscope from the early 90s. The analog traces work perfectly, but after using it a while the digital cursors and readouts started moving downwards and out of the screen. Now when the scope is powered on, the last row of numbers is partly out of the screen. After a while it goes even further. Of course when the scope is in digital mode, the trace also moves out of screen. Sometimes everything on the screen disappears, but returns when restarting the scope.

What can be the cause of this? Bad capacitors? I have tried to find a service manual online but with no luck. There are many trimmers inside the scope, but I'm afraid to touch anything, since the problem is not constant.


Thanks in advance,

Jan

[SMdude]

I don't have a manual, but the first thing I would do, given that it is (was)ok when cold, but no good after "warming up" would be to carefully warm (hot air solder station is ideal)around the board(with everything cold) and see which area you hit to cause it to show the problem.
From there you can probably narrow it down.
A can of freeze spray may be handy too.
Don't let the scope bite you!
I'd be looking at any electro's in the suspect area first.

Good luck!
If the above doesn't do anything for you then a schematic will be the best help.

[JanR]

Thank you. Heating with a hot air station is a good idea. I'll try that.

I also contacted Kikusui and they were kind enough to send the service manual. 

I'll keep you updated on the progress.