I've had problems like that in the past with analog scopes. You can verify
that it is not the trigger circuit by simply not triggering it. Leave the
trigger on auto & turn the trigger level way up.
Most likely you have a problem in the vertical amp section or in the
vertical deflection driver.
If you are really seeing a worse problem when you adjust the volts/division,
then you may simply have a switch with bad contacts. I've got a kenwood with
this exact problem. Contact cleaner on the volts/div switch makes the
problem go away for a year or two.

Changing the switch will likely be tricky even if you can get a replacement.
If the switch is an open type where you can see the contacts you may have
more luck cleaning it.

Joe

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Marcel Birthelmer
> Sent: 06 July 2006 04:00
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] scope jumps
> 
> 
> 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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