slanted oscilloscope traces

[dfuruta]

A few weeks ago, my oscilloscope started doing this.  Has anyone seen this before?  Is there some easy cure?

My thought is maybe something got magnetized, but I'm not at all sure that's right.

 

[JohnRoberts]

bummer

JR

 

[RuudNL]

Just a wild guess: the flyback suppression?

 

[ruffrecords]

WOW, you invented time travel! That downward trace goes backwards in time.

One of the kids hasn't stuck a fridge magnet on the side of the scope have they??

Most scopes use electrostatic deflection so it's not likely to be a scope fault. However, most of them use steel cases which can get magnetised.

Cheers

Ian

 

[dfuruta]

WOW, you invented time travel! That downward trace goes backwards in time.

One of the kids hasn't stuck a fridge magnet on the side of the scope have they??

Most scopes use electrostatic deflection so it's not likely to be a scope fault. However, most of them use steel cases which can get magnetised.

Cheers

Ian

Yeah, I didn't realize I'd accidentally fired up the flux capacitor!

I wondered if the case (or something else) getting magnetized might have caused this.  Maybe I'll try degaussing it.

 

[JohnRoberts]

The apparent time travel may simply be an artifact of triggering. While the display is presumably of a single sweep, it is really displaying multiple snapshots.

JR

 

[Andy Peters]

A few weeks ago, my oscilloscope started doing this.  Has anyone seen this before?  Is there some easy cure?

My thought is maybe something got magnetized, but I'm not at all sure that's right.

When was the last time you checked your probe compensation? That's what those little screws in the probe body are used for.

-a

 

[s2udio]

Yup with Andy there ,, check the probes and give em a twiddle

 

[dfuruta]

It's not probe compensation, nor is it the trace rotation;  this behavior is consistent with different probes (all of them compensated) & signal sources.  The picture in the first post is using the built-in signal generator.

Could probe compensation actually lead to an issue like this?  Can't imagine it would...

 

[gyraf]

Try moving a magnet around the outside of the scope to see if you can compensate - that'll show if this is the problem. I had something like this on a very-old tek I had once, "cured" by rotating the mu-metal screen around the crt.

Jakob E.

 

[JohnRoberts]

It's a strange one... looks crt or drive related. the raster is shifted in time. I don't know if external magnetic fields effect that, it could.

One test is to try a different square wave, but no negative time steps in real life so looks like scope is a little squirrely.

JR

 

[PRR]

If the verticals are not 90.00 degrees to the horizontal, the internal deflection plates have been bent.

For a ~~1deg error: Tilt your head and get on with life. 

 

[dfuruta]

Try moving a magnet around the outside of the scope to see if you can compensate - that'll show if this is the problem. I had something like this on a very-old tek I had once, "cured" by rotating the mu-metal screen around the crt.

Jakob E.

I tried this yesterday, and I was able to straighten out the traces to an extent with a magnet (the parts of the trace close to the magnet were straight, the ones farther away were distorted).

Hopefully the problem is just something getting magnetized, and not the plates getting bent or something weird in the drive circuit.  I have Monday off from work, so I'll experiment further then.

re JohnRoberts, looks like the problem's there with other signal sources, too.

re PRR, it's certainly still usable, but kind of confusing - with square waves, it's obvious that the scope is malfunctioning, but sine waves looked screwed up in a subtler way.

 

[dfuruta]

Took a 1000' spool of 22awg wire, put it on top of the scope & ran it up very slowly to a couple amps and back down with a variac.  Hey presto, the scope's back to normal!

 

[fpliuzzi]

Clever idea. That was a pretty resourceful way for you to come up with a quick degaussing coil.

FPL