Author Topic: Elenco s-1325 slanted trace  (Read 13923 times)

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Offline miguelvp

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Re: Elenco s-1325 slanted trace
« Reply #50 on: July 08, 2014, 03:03:45 am »
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.
« Last Edit: July 08, 2014, 03:11:05 am by miguelvp »
 

Offline tautech

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Re: Elenco s-1325 slanted trace
« Reply #51 on: July 08, 2014, 03:14:08 am »
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.
Quote
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?
Quote
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?
Quote
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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Offline jmctech

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Re: Elenco s-1325 slanted trace
« Reply #52 on: July 08, 2014, 03:18:58 am »
The power supply has a variable  resistor.
 

Offline tautech

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Re: Elenco s-1325 slanted trace
« Reply #53 on: July 08, 2014, 03:33:55 am »
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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Offline Joule Thief

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Re: Elenco s-1325 slanted trace
« Reply #54 on: July 08, 2014, 06:51:45 am »



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.


Perturb and observe.
 

Offline miguelvp

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Re: Elenco s-1325 slanted trace
« Reply #55 on: July 08, 2014, 07:25:26 am »
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.


 

Offline Joule Thief

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Re: Elenco s-1325 slanted trace
« Reply #56 on: July 08, 2014, 07:43:50 am »
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.
Perturb and observe.
 

Offline miguelvp

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Re: Elenco s-1325 slanted trace
« Reply #57 on: July 08, 2014, 07:49:18 am »
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.
 

Offline Joule Thief

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Re: Elenco s-1325 slanted trace
« Reply #58 on: July 08, 2014, 08:10:55 am »
 :-+ 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".
« Last Edit: July 08, 2014, 08:21:02 am by Joule Thief »
Perturb and observe.
 

Offline miguelvp

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Re: Elenco s-1325 slanted trace
« Reply #59 on: July 08, 2014, 08:13:35 am »
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.



Edit: that came out at pretty low res, adding the layout picture from the doc.


The way I understand this, pins 5, 6, 12 and 13 should be all connected in that connector board.
« Last Edit: July 08, 2014, 08:21:18 am by miguelvp »
 

Offline onlooker

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Re: Elenco s-1325 slanted trace
« Reply #60 on: July 08, 2014, 12:39:01 pm »
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.
« Last Edit: July 08, 2014, 12:42:06 pm by onlooker »
 

Offline miguelvp

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Re: Elenco s-1325 slanted trace
« Reply #61 on: July 08, 2014, 02:29:07 pm »
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.
« Last Edit: July 08, 2014, 02:41:00 pm by miguelvp »
 

Offline Electronics-Repairman

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Re: Elenco s-1325 slanted trace
« Reply #62 on: July 08, 2014, 03:03:03 pm »
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.
If it's highly recommended, then  I'm not interested.
 

Offline PointyOintment

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Re: Elenco s-1325 slanted trace
« Reply #63 on: September 14, 2014, 03:49:22 am »



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.

Offline George Kaplan

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Re: Elenco s-1325 slanted trace
« Reply #64 on: May 19, 2019, 10:30:50 pm »
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.
« Last Edit: May 20, 2019, 05:54:12 pm by George Kaplan »
 


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