B&K Precision 2125 Oscilloscope Vertical Shift

[rsaxvc]

About a year ago I picked up quite a bit of test equipment, including several dual-trace analog oscilloscopes, a few of which have this issue where the vertical channel shifts up and down for a bit. It doesn't happen reliably, but often happens for a couple minutes on and off. Unless I'm monitoring something - then it works fine.

I've got a short video of it here:

It affects both channels similarly, independent of the vertical scale - I think this means that the problem is either after the preamps in the vertical amp or in something that affects both preamps similarly like a power supply. I figured I'd ask if anyone had seem something similar or might have some direction on where I should look next.

Todo/ideas:

• check XY mode to see if it affects horizontal amp
• check low/mid voltage power supplies with a scope - nothing interesting with a DMM

[bdunham7]

I'd take the cover off and try carefully wiggling all the various inter-board connections, jumpers and grounds to see if something is a bit loose.

[Wallace Gasiewicz]

I second the cleaning of connections and cleaning the pots and inputs.
Maybe even a bad solder joint.

[med6753]

If you checked the PSU voltages and they are OK then concentrate on an issue in the vertical amplifier. That's vertical shift, not horizontal shift.