Elenco s-1325 slanted trace

[jmctech]

Hi everyone, this is my first post I apologize if it is in the wrong spot. I got my first scope an Elenco s-1325 off craigslist. It came with 2 probes.  When I hook either probe up to the calibration pin my square wave is slanted. This is what it looks like with time set at .5 mS and volts at .5. Cal pin says 2v P-P.




If this a fixable issue or did I get taken. I paid $50 for the scope. It shows the same on both channels. Thanks for any help you guys can provide.

Jason

[miguelvp]

did you try to adjust the trace rotation? or does that rotates the whole signal?
right in the middle of Intensity and Focus

Edit: Then again it could be something to do with the deflectors on the actual CTR that got dislodge during shipping but be careful there is high voltage in there. Even if unpluged you gotta be careful.

[jmctech]

The trace rotation does the whole signal.

[miguelvp]

Looks like the vertical deflection is tilted. Maybe someone else can chime in.

I couldn't find any pictures of the insides of your scope specially the coils around the CRT tube.

I couldn't find a service manual either, just the user manual.

[tautech]

Looks like the vertical deflection is tilted. Maybe someone else can chime in.

I couldn't find any pictures of the insides of your scope specially the coils around the CRT tube.

I couldn't find a service manual either, just the user manual.

CRT Oscilloscope's don't use defection coils.

I've fixed a few CRT scopes but have never seen one with a negative rise time. 

But the display seems to displaying as it should, however an incorrect signal.

Have you any manuals for the scope?

This will surprise many and I for one will be very interested in the progress of this thread.

C'mon Super Contributors give us some clues.

Edit
OP could this be a combination of incorrectly compensated probe and trace rotation?
To check, adjust trace with no signal input and a fine focus setting to match graticule lines.
Then adjust probe.

[miguelvp]

Maybe not coils around the CRT neck but it looks like the vertical deflection (even if it's inside the tube) is tilted.

(image from: http://www.ic.sunysb.edu/Class/phy122ps/labs/dokuwiki/doku.php?id=phy124:lab_2)
That's the only thing I can think that will make this happen.

edit:

Edit
OP could this be a combination of incorrectly compensated probe and trace rotation?
To check, adjust trace with no signal input and a fine focus setting to match graticule lines.
Then adjust probe.

That can't be because the falling edges are aligned.

[Richard Head]

What you have discovered is proof of the existance of tachyons! This scope is indeed displaying signals traveling backwards in time.
The square wave generator must contain a flux capacitor as its timing capacitor.

[tautech]

What you have discovered is proof of the existance of tachyons! This scope is indeed displaying signals traveling backwards in time.
The square wave generator must contain a flux capacitor as its timing capacitor.

Beautiful. 

[tautech]

@miguelvp
Yes the deflection plates may have been bent by way of impact to the scope, though it seems unusual that they seem bent both the same amount.
@jmctech
Jason, are there any signs of impact on the case?

[tautech]

Jason
Supply a sawtooth test waveform and photograph the result for us please.

[miguelvp]

It can also be whatever is controlling the vertical deflection that is acting up somehow.
So it might not be the deflection plates themselves but something related to the control of the vertical trace being out of sync.

[tautech]

@miguelvp
I suspect scope is displaying a "reverse" sweep.
That is: the horizontal plate wires have been reversed. 

A great trick to play on a buddy. 

[PA0PBZ]

I think it is just trace rotation and a sloppy calibration signal. Set the input to GND, use trace rotation to make the line horizontal and then use a better signal to see what it looks like.

[AlfBaz]

Has this scope got XY mode?
If so place a signal in one channel and then the next. You should should get a small horizontal line in one channel and a vertical in the other.

By rights the vertical one should be slanted

[leppie]

Got a big magnet or speaker next to the scope?

I know my variable SMPS causes my TDS340 to go ape-shit when next to it.

[Joule Thief]

To check trace rotation, place the CH1 coupling to GND position and place the trace line over one of the horizontal graticules. The trace should stay on the graticule across the entire CRT screen. Trace rotation will correct any linear departure from the graticule line.

To check for reversed horizontal sweep. set the HORIZ SWEEP SPEED to a low speed and observe the "dot" trace move left to right across the CRT. If the "dot" moves right to left, then the trace direction is reversed - maybe the CRT is upside down?

[PA0PBZ]

maybe the CRT is upside down?

No, rotating the picture 180 will not make it look any better.

[PA0PBZ]

Even mirroring does not do the trick.

[AlfBaz]

Neither does embossing

[PA0PBZ]

Neither does embossing

Hey there, I'm just trying to tell that the tube is not upside down or that the plate connections have been swapped, you are just bragging about your embossing talent 

[miguelvp]

Maybe the OP could open up the unit and take pictures of the tube neck and control boards around it.

[jmctech]

So I used an arduino and a 1uf cap and it still shows negative rise time.




I did get the service manual with it but do not have the equipment to calibrate it. I don't have a waveform generator.

Here is a pic of the inside,

[PA0PBZ]

Do you have a horizontal line without input (or set to GND)?

[jmctech]

Yes, it's the same on both channels

[PA0PBZ]

Yes, it's the same on both channels

Hmm, I do get the idea that the X-position is somehow getting distorted by the Y-deflection.
If you decrease the X sensitivity, does that give you a lesser negative effect?
You say that you have the service manual, so start by checking the power supply.