Could it be that your trigger level is set to something very close to
the signal level you're looking at so that it briefly loses sync every
once in a while?
- Marcel

Martin Klingensmith wrote:
> I'll be using my scope and both traces will jump up or down seemingly
> randomly once every several seconds (not periodically). Both traces are
> set to DC. It doesn't seem to matter what time/div setting I have it on.
> It may happen more frequently when I play with the vertical positions
> but perhaps it's because I'm staring at it when I do that.
> 
> I thought it might be a grounding issue but the signal generator and
> scope probe grounds are hooked directly together.
> 
> The scope is an HP 1220A and it is several years old I'm sure. Perhaps
> there might be something internally I could adjust or calibrate or
> replace, and you would know which part causes this symptom? (hey I can
> try, right?)
> 
> Thanks.
> 
> --
> Martin K
> 
> 
> 

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