EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: jmctech on July 07, 2014, 04:49:41 am
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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.
(http://img.tapatalk.com/d/14/07/07/dasasane.jpg)
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
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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.
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The trace rotation does the whole signal.
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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.
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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. :wtf:
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.
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Maybe not coils around the CRT neck but it looks like the vertical deflection (even if it's inside the tube) is tilted.
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101013;image)
(image from: http://www.ic.sunysb.edu/Class/phy122ps/labs/dokuwiki/doku.php?id=phy124:lab_2 (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.
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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.
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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. :-DD
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@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?
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Jason
Supply a sawtooth test waveform and photograph the result for us please.
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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.
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@miguelvp
I suspect scope is displaying a "reverse" sweep.
That is: the horizontal plate wires have been reversed. :-DD
A great trick to play on a buddy. >:D
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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.
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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
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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.
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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?
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maybe the CRT is upside down?
No, rotating the picture 180 will not make it look any better.
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Even mirroring does not do the trick.
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Neither does embossing ;D
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101047;image)
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Neither does embossing ;D
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 :P
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Maybe the OP could open up the unit and take pictures of the tube neck and control boards around it.
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So I used an arduino and a 1uf cap and it still shows negative rise time.
(http://img.tapatalk.com/d/14/07/08/3u4e3e9e.jpg)
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,
(http://img.tapatalk.com/d/14/07/08/e8ubedum.jpg)
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Do you have a horizontal line without input (or set to GND)?
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Yes, it's the same on both channels
(http://img.tapatalk.com/d/14/07/08/e3y4ymy2.jpg)
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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.
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Can you see any evidence that the yellow coil - half-way along the tube - has been jarred out of its correct position? You could try disconnecting the coil - follow the white and red wires.
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BTW here is some info for the CRT:
http://tubedata.milbert.com/sheets/186/d/D14363GY123.pdf (http://tubedata.milbert.com/sheets/186/d/D14363GY123.pdf)
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Can you see any evidence that the yellow coil - half-way along the tube - has been jarred out of its correct position? You could try disconnecting the coil - follow the white and red wires.
That would be the trace rotation coil affixed with resin, it would affect the whole signal.
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Coil looks good, it has 4 epoxy spots that are solid
(http://img.tapatalk.com/d/14/07/08/a9aravum.jpg)
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Note 2 of the CRT pdf linked above
The deflection plates must be operated symmetrically. Asymmetric drive introduces trace distortion.
It is recommended that the tube is operated with equal mean x- and y-potentials in order to
minimize tube adjustments. In this event g5 may be connected to g2, g4 and all made equal to mean
y-potential for optimum spot (see also notes 3 and 4).
A difference between mean x- and y-potentials up to 75 V is permissible. However, this may
influence the specified deflection coefficients and separate voltages on g4 and g5 will be required.
Edit, but careful we are talking about 2KV here.
Also the CRT has astigmatic correction, I wonder if that has a front know control and if it will affect the signal's orthogonality as mentioned in note 9 of the above doc.
The tube features internal magnetic correction for orthogonality between x- and y-traces, spot
shaping (astigmatism) and eccentricity calibration.
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I tested all power supply leads
Manual shows 140 meter showed 150
Manual showed 12 meter at 12.6
Manual showed 16 for two they were at 16.89 and 16.04
Manual showed 31 and 6.3 on the isolation for the crt was at 7.14 and 34.8
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This is what displays when in x - y
(http://img.tapatalk.com/d/14/07/08/ejydu5yq.jpg)
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Also the CRT has astigmatic correction, I wonder if that has a front know control and if it will affect the signal's orthogonality as mentioned in note 9 of the above doc.
The tube features internal magnetic correction for orthogonality between x- and y-traces, spot
shaping (astigmatism) and eccentricity calibration.
More about note 9
Angle between x and y traces 90 ± 0.5° (note 9)
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Next test should be the ramp generator for the sweep.
You will want to see a clean linear sawtooth waveform.
You will need another scope for that test.
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just an idea Guys....
if the there is a common supply for X and Y deflection... can't it simply be that the power rail is weak and causing this ? or there is some other interference between X&Y amplifiers ? because for example: once Y starts to deflect the beam and it puls down the voltage for the X deflection... then it would produce similar effect (X goes backwards)... and similarly for the the falling edge - Y decreases deflection of the beam and the voltage for X raising back to "normal" (X goes forward faster than should).
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A picture of the controller board from the back (the board tilted about 13 to 19 degrees) might help to see how the g2,g4 and g5 are connected.
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Since you mentioned that you have the service manual, can you find where the astigm and geom pots are if anywhere?
and post pictures of the schematic that connects to the CRT?
for example something like this:
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101077;image)
Edit: Again a reminder to be careful, because there are very high voltages there. Maybe if you have a friend that repairs TVs they might be helpful.
I would only try to adjust them with the power off myself and only with a plastic tool and my free hand in my pocket, high voltages scare me.
I have no idea on your level of confidence dealing with 2,000 Volts.
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(http://img.tapatalk.com/d/14/07/08/qe7uguhy.jpg)
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Here is the other board you asked about
(http://img.tapatalk.com/d/14/07/08/y5utyzub.jpg)
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Can you check in the manual if VR822 is the astigmatism adjustment? and were is it located in your board?
I believe is the one on the upper left of this image you posted earlier next to that 3 pin connector that I'm guessing it connects to the CRT board but I can't see it from the picture you posted.
Edit: linking to your image didn't work so here is the section I'm talking about
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101081;image)
Is the connector labeled P802 and is that pot labeled VR822?
And does the manual refer to it as the Astigmatism adjustment?
It might need to be adjusted or the cap C808 is doing something funny. (Edit: if that is a cap at all, looks blurry to me)
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101085;image)
Edit: This is an educated guess, someone please chime in if you think this will fix the orthogonality between x and y
Edit again: The red cable on that connector should trace all the way to pin 13 of the CRT connector.
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This is what displays when in x - y
In that picture you have a signal to both channels in XY mode?
I was curious to see what the vertical trace looked like.
Checking the horizontal is easy, ground the input and you should have no vertical deflection or rotation and can be seen by looking at the line and comparing it to the graticule.
To do the same for the vertical you need to apply a varying voltage on the vertical but eliminate the internal horizontal sweep
So in XY mode , if you put the signal to only one channel at a time, on one you should get a nice horizontal line and the other a nice vertical line, or in this case a line slanted back, thereby concluding that it is actually the deflection plates/circuit.
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you are just bragging about your embossing talent :P
LOL, I've been waiting for an excuse to post one for ages :D
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I tested all power supply leads
Manual shows 140 meter showed 150
Manual showed 12 meter at 12.6
Manual showed 16 for two they were at 16.89 and 16.04
Manual showed 31 and 6.3 on the isolation for the crt was at 7.14 and 34.8
Your measurements show ALL voltages above spec.
2 questions:
Is your meter accurate?
Is the scope mains input selector set for the correct mains voltage in your location?
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Yes I check that it is set for 120
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Yes I check that it is set for 120
I strongly suggest you change the mains input voltage selector to a lower voltage.
All components in the scope will be subjected to higher than design voltages with the existing input selection.
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The only options I have is 120 and 240
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This is what the vertical looks like
(http://img.tapatalk.com/d/14/07/08/qymuhe5u.jpg)
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Can you check in the manual if VR822 is the astigmatism adjustment? and were is it located in your board?
I believe is the one on the upper left of this image you posted earlier next to that 3 pin connector that I'm guessing it connects to the CRT board but I can't see it from the picture you posted.
Edit: linking to your image didn't work so here is the section I'm talking about
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101081;image)
Is the connector labeled P802 and is that pot labeled VR822?
And does the manual refer to it as the Astigmatism adjustment?
It might need to be adjusted or the cap C808 is doing something funny. (Edit: if that is a cap at all, looks blurry to me)
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101085;image)
Edit: This is an educated guess, someone please chime in if you think this will fix the orthogonality between x and y
Edit again: The red cable on that connector should trace all the way to pin 13 of the CRT connector.
VR 822 is the astigmatism adjustment.
Manipulating it makes no difference in the slant though.
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That's odd since it's connected to g2, g4 and g5 it should change both the geometry and the astigmatism.
At least it should make the traces wider on the bottom or narrower depending on the direction. Maybe there is something with that part of the circuit. Still not sure what C808 is, Anyone knows if the NPN transistor Q805 could cause this problem? or the capacitors C809 and whatever C808 is? (looks like a blob to me)
BTW here are the notes of the CRT document
NOTES
1. Because the frit seal is visible through the faceplate, and is not necessarily aligned with the internal
graticule, application of an external passe-partout with an open area of max. 102 mm x 82 mm is
recommended. The internal graticule is aligned with the faceplate by using the faceplate reference
points (see Fig.4).
2. The deflection plates must be operated symmetrically. Asymmetric drive introduces trace distortion.
It is recommended that the tube is operated with equal mean x- and y-potentials in order to
minimize tube adjustments. In this event g5 may be connected to g2, g4 and all made equal to mean
y-potential for optimum spot (see also notes 3 and 4).
A difference between mean x- and y-potentials up to 75 V is permissible. However, this may
influence the specified deflection coefficients and separate voltages on g4 and g5 will be required.
3. The tube will meet the geometry specification (see note 8 ) if Vg5 is equal to mean x-potential. A
range of ± 30 V around mean x-potential may be applied for further correction.
4. Optimum spot is obtained with Vg2,g4 equal to mean y-potential (see note 2). Generally, a tolerance of
± 4 V has no visible effect. Vg2,g4 tends to be lower with Vg5 more positive. The circuit impedance
Rg2,g4 should be less than 10 kOhm.
5. An actual focus range of 30 V should be provided on the front panel. Vg3 decreases with increasing
grid drive (see also Fig.5).
6. Intensity control on the front panel should be limited to the maximum useful screen current (approx.
50 µA; see also Fig.5). It should be adjusted either by the grid drive voltage (up to 22 V) or for
maximum acceptable line width. The corresponding cathode current or Ig2,g4 (up to 500 µA) depends
on the cut-off voltage and therefore cannot be used for control settings.
7. The sensitivity at a deflection of less than 75% of the useful scan will not differ from the sensitivity at
a deflection of 25% of the useful scan by more than the indicated value.
8. A graticule consisting of concentric rectangles of 100 mm x 80 mm and 98 mm x 78 mm is aligned
with the internal graticule. With optimum trace rotation correction, the raster will fall between these
rectangles.
9. The tube features internal magnetic correction for orthogonality between x- and y-traces, spot
shaping (astigmatism) and eccentricity calibration.
10. The tube has a trace rotation coil fixed to the lower cone part. The coil has a maximum resistance of
260 Ohms at 80 °C. The maximum required voltage is approximately 11 V for tube tolerances (± 5°) and
earth magnetic field with reasonable shielding (± 2°).
11. Measured with the shrinking raster method in the centre of the screen under typical operating
conditions, adjusted for optimum spot size at beam current Il = 10 µA.
The beam current Il can be measured on g5 and is approx. equal to Ig5(l).
and the link again to said document:
http://tubedata.milbert.com/sheets/186/d/D14363GY123.pdf (http://tubedata.milbert.com/sheets/186/d/D14363GY123.pdf)
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I belive what I am going to have to do is buy a waveform generator and calibrate it from the service manual to see if that helps. Looking through the manual it shows that there is VR for the power supply which sets all voltages that I measured earlier. It does also talk about a vertical and horizontal amp adjustment. Could either of those have anything to do with it? I want to thank everyone for their input so far also.
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Good luck with your repair. Even if it's slanted it's kind of usable for square waves.
I find it strange the astigmatism doesn't do a thing.
Otherwise it could be something to do with note 2 above since g5 g2 and g4 are connected the x and y potentials have to be symmetric, but VR 822 not doing a thing looks suspicious to me.
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I belive what I am going to have to do is buy a waveform generator and calibrate it from the service manual to see if that helps. Looking through the manual it shows that there is VR for the power supply which sets all voltages that I measured earlier. It does also talk about a vertical and horizontal amp adjustment. Could either of those have anything to do with it? I want to thank everyone for their input so far also.
I belive what I am going to have to do is buy a waveform generator and calibrate it from the service manual to see if that helps.
You will not be able to do a proper cal with WG or FG. Maybe an AWG for a scope like this.
A simple ramp gen will do to check sweep results.
Somebody might like to offer a circuit?
Looking through the manual it shows that there is VR for the power supply which sets all voltages that I measured earlier.
VR meaning adjustment or voltage regulator?
It does also talk about a vertical and horizontal amp adjustment. Could either of those have anything to do with it?
Unlikely IMO.
There is a fault with one of the core parts of the scope
Your pics show correct amplitude, timebase and display parameters.
I suspect the linearity of the sweep generator.
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The power supply has a variable resistor.
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The power supply has a variable resistor.
Often CRT scope multi-voltage regulated supplies are referenced from 1 adjustable supply.
Check your manual for the adjustment procedure, follow it and the critical V+ rails should come to spec.
There will be some V+ rails that are unregulated, and the manual usually has a wider V+ range for their spec.
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(http://i880.photobucket.com/albums/ac4/save_old_iron/errata/scopetrace_zps6985841d.gif)
Am I getting anywhere near understanding of this issue?
Let us take a slight liberty with rise / fall times for the sake of argument and say point B and point A should be DIPSLAYED as the same time per the horizontal graticule. How do we interpret a part of the waveform to exist at the same time as another part of the waveform? Visual interpretation from the PHYSICAL position of the waveform along the HORIZONTAL graticule.
During the rise of the voltage level from point B to point A, the electron beam striking the CRT moves very little along the horizontal axis but makes a significant jump upward due to significant voltage changes on the vertical deflection grids. The vertical change in the position of the electron beam causes the beam to change its position relative to the top and bottom area of the horizontal deflection grid.
Assume the black line labeled CB (horizontal grid bottom) and GT (horizontal grid top) represents one of the damaged (tilted) horizontal deflection grids. As the electron beam changes position to a higher position within the horizontal grid (point A), and since no significant voltage change occurs on the horizontal (time) grid during the A to B transistion time, the electron beam should remain the same distance away from the horizontal grid. The electron beam does remain in the same position relative to the horizontal grid but if the horizontal grid GB –GT tilts to the left, the electron beam will also travel to the left as the beam rises vertically. The end result is the physical placement of the beam “back in time” along the horizontal time axis.
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Sounds right and that will apply to note 2 of the CRT document. The thing is that the astigmatic adjustment has no effect as per the OP, maybe he didn't turn it too much to be conservative but it should have done something instead of no effect unless that wasn't the right pot (should be labeled VR822 but it's not in view from the picture he posted).
But if it's not that pot, then inote 2 implies that the problem is a discrepancy between the x and y potentials since g2, g4 & g5 are connected according to the schematic he posted.
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I know this is not the issue, but did we ever try the trace rotation control just to see if it was operational? Sometimes a problem is isolated by first finding out what does function as expected.
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I know this is not the issue, but did we ever try the trace rotation control just to see if it was operational? Sometimes a problem is isolated by first finding out what does function as expected.
Post #2 and OP's reply post #3
It rotates the whole signal, no pictures posted i'm afraid.
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:-+ Thanks. Was not sure if he had confirmed proper operation of the trace rotation or was just putting forward his understanding the whole trace would be affected and not just the "tilt".
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A good picture of the back of the CRT neck connector will help.
Maybe the connection between pin 12 and pin 13 is disconnected and that's why the pot has no effect since it's only driving g4 and not g2 and g5 if the connection is not there.
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101115;image)
Edit: that came out at pretty low res, adding the layout picture from the doc.
(https://www.eevblog.com/forum/testgear/elenco-s-1325-slanted-trace/?action=dlattach;attach=101119;image)
The way I understand this, pins 5, 6, 12 and 13 should be all connected in that connector board.
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The pinouts and diagrams shown are not consistent?
Anyway, if vr822 has no effect, then check if q805 is working properly:
-- the160V power rail. Is this the same one also labelled 140V?
-- the base voltage. Does it change with vr822 with enough swing?
-- the emitter voltage. Does it follow the base voltage?
Then, check in xy mode, the votages btw gnd and y-, y+, x-, x+ respectively.
These are just to check if the oscope is still in spec as described in those notes.
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The pinouts and diagrams shown are not consistent?
Anyway, if vr822 has no effect, then check if q805 is working properly:
-- the160V power rail. Is this the same one also labelled 140V?
-- the base voltage. Does it change with vr822 with enough swing?
-- the emitter voltage. Does it follow the base voltage?
Then, check in xy mode, the votages btw gnd and y-, y+, x-, x+ respectively.
These are just to check if the oscope is still in spec as described in those notes.
careful where the 2000 Volts are if you are going to check this,you need high voltage probes too.
Myself I would leave that to a shop or someone that works with high-voltages.
Also what type of DMM do you have as in brand/model, might not be good for these kinds of measurements. (yeah i'm being overcautious but this is a dangerous area to be poking around)
The pinouts on the diagram are looking from the back of the connector btw so they do match.
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Hope you solve it , beware if you stick your hand inside it may bite, remember it's a case of one hand in your pocket , and NO metal work like rings or chains, I know it's boring stuff, but it's the boring stuff that keeps you alive.
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(http://i880.photobucket.com/albums/ac4/save_old_iron/errata/scopetrace_zps6985841d.gif)
Am I getting anywhere near understanding of this issue?
Let us take a slight liberty with rise / fall times for the sake of argument and say point B and point A should be DIPSLAYED as the same time per the horizontal graticule. How do we interpret a part of the waveform to exist at the same time as another part of the waveform? Visual interpretation from the PHYSICAL position of the waveform along the HORIZONTAL graticule.
During the rise of the voltage level from point B to point A, the electron beam striking the CRT moves very little along the horizontal axis but makes a significant jump upward due to significant voltage changes on the vertical deflection grids. The vertical change in the position of the electron beam causes the beam to change its position relative to the top and bottom area of the horizontal deflection grid.
Assume the black line labeled CB (horizontal grid bottom) and GT (horizontal grid top) represents one of the damaged (tilted) horizontal deflection grids. As the electron beam changes position to a higher position within the horizontal grid (point A), and since no significant voltage change occurs on the horizontal (time) grid during the A to B transistion time, the electron beam should remain the same distance away from the horizontal grid. The electron beam does remain in the same position relative to the horizontal grid but if the horizontal grid GB –GT tilts to the left, the electron beam will also travel to the left as the beam rises vertically. The end result is the physical placement of the beam “back in time” along the horizontal time axis.
I disagree. Both horizontal deflection plates being tilted the same amount should make no difference to the horizontal deflection of the electron beam. The E-field is uniform between them (across the width of the tube), so the electrons being closer to one plate than the other at the top or bottom wouldn't matter. If just one plate was tilted, then the E-field would be stronger between the closer ends of the plates, but it would be stronger in both directions, causing the horizontal deflection to be greater both right and left (from the center) at the top or bottom, which would look like the effect of the keystone adjustment on a projector. The only way plate position/angle could cause the effect shown is if the vertical deflection plates were rotated together (as a group) about the axis of the tube.
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I realize that this is an old thread, but the subject pops up from time to time on the web, with lots of well-meaning, but wrong, advice. This post is for the next person who searches for a solution.
If an undeflected baseline or the tops of a square wave are flat, then it isn't a trace rotation problem. A magnetized shield could cause odd geometric distortion, so degaussing it is always a good thing to try. One needn't fear damaging the CRT (unless you physically strike the glass; just don't do that).
If the problem persists, you'll have to look deeper.
"Bent deflection plates" seems to be a popular guess, but it's the least likely explanation. Anything capable of bending plates would almost certainly destroy the jug. In any case, if the plates had broken loose, it would be easy to verify -- tapping the scope would affect the deflection in a very obvious way. But the guess, wrong as it is, does point in the right general area. There are many electrodes inside a CRT and they can all affect deflection. In many (but not all) CRTs there is one appropriately called the geometry electrode, which affects linearity over the entirety of the deflection area. When it's biased wrongly, a square trace would appear trapezoidal. And that's what most often causes the slanted trace problem (once trace rotation is correctly set). A poster already brought up this possibility but the thread sort of explored a larger space.
In many scopes with this problem, the wiper of the trimpot ontrolling the geometry electrode voltage has simply gotten a bit dirty, and giving it a back and forth tweak will set things right. In other cases, a bypass cap has shorted, or another resistor has failed. Just look for a trimpot labeled something like "GEOM" and sniff around that region. The fix is usually trivial.
In the case of this particular scope, the schematics don't show any provision for adjustment of the electrode voltage in question. However, the OP did note that the power supply voltages were high by a relatively large amount. Fixing that problem should be the first order of business, as supply voltage errors can cause a variety of confounding symptoms.
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Once again reviving this old thread just in case someone else in the future is looking for S-1325 schematics. It shares significant commonality with the 30MHz BK precision 2120B (the original 2120 is different!), for which I was able to find schematics for here: http://www.ko4bb.com/getsimple/index.php?id=manuals (http://www.ko4bb.com/getsimple/index.php?id=manuals)