Oscilloscope horizontal line is curved. How fix this?

[ginji]

Thanks for your comments.
I don't remember giving the deflector plate a deforming shock and external magnetism.
I was using it normally and this problem occurred.

[ambrosia heart]

Hello.
My analog oscilloscope (IWATSU SS-6421) also has a curved horizontal line.
When the horizontal line is at the center of the top and bottom, it is not curved, but when I move it upward or downward, it is curved.
The readout display is also curved.
What is the cause? Please help!
(Attachment Link)

CRT is damaged. fixing is impossible except replace a good one.  You can buy a 2nd hand 400MHz at 闲鱼 at 1660RMB. There are a lot of japaneses living in Tai Wan, calling them for help such as 心奈，夢多 and 小百合。 Contract them via their facebook.  Taiwaneses are friendly

[ginji]

To the people of Taiwan, we are very grateful for the support we received after the March 11, 2011 earthquake and tsunami.
I have a Taiwanese friend in Taipei whom I respect.
Thank you for your accurate advice.

[ginji]

If it is a deformation of the deflector plate inside the CRT, would the curve of the line be contrasting between the top and bottom?
I like to think that the cause of this problem is the vertical deflection, I would like to know what kind of cause?

[ambrosia heart]

If it is a deformation of the deflector plate inside the CRT, would the curve of the line be contrasting between the top and bottom?
I like to think that the cause of this problem is the vertical deflection, I would like to know what kind of cause?

see pm and use google translate.
 contact TaiWan Japanese 夢多，心奈，小百合to help you.
Buy another 2nd hand to use < 1000RMB.

[jonpaul]

sorry very vague post. "horizontal line is curved" can mean anything....how much? Curve shape? Trace clear or out of focus? Changes with intensity or signal?

How can we respond without  good photos of  your problem.

I doubt that magnetization has anything to do with this.

if you can  post a photo,  we can diagnose.


Jon

[Wallace Gasiewicz]

Some oscilloscope tubes have a "Yoke" that goes around the neck of the tube.
I think this is called a trace rotation coil.
If this shifts it can cause the image on the screen to deform.
If this is the problem, you can rotate the "Yoke" back to it's proper position.

I do not know if your scope has a Yoke or not. Please let me know.

[bdunham7]

See if the adjustment marked ASTIG has any effect on that.

[ginji]

The image with the curved line is on yesterday's page. But I will post it again.
There is no deflection coil on the CRT of this oscilloscope, so the deflection coil cannot be adjusted.

[ginji]

I will disassemble the oscilloscope to see if this CRT has a trace rotation coil.

[bdunham7]

If it has a trace rotation adjustment, it must have a coil.  But that is not going to be your problem.

I wanted to have you adjust the astigmatism to see if it has a uniform effect on the focus over the whole screen or if it varies--you would be able to see this by looking at the readout text.  I'm thinking it will be uniform because I don't think you have a problem with the CRT or the gun/focus/astig section of the circuitry.  It looks like the vertical amp loses gain when the horizontal amp is at the edges of the scope.  If they have a common power supply--and they likely do--then there could simply be a problem with that power supply being weak.  The power supply is the first place to look when an old CRO goes haywire.

[ginji]

Mr. bdunham7

Thank you for your very accurate comments.
I have confirmed that the power supply voltage of 5V, 12V, 50V and 150V is normal. However, I haven't checked the high voltage applied to the CRT yet, that is the high voltage of the second anode, final anode and other grids. I am thinking that maybe the acceleration voltage of the electron beam is not enough.
These voltages range from 2KV to 16KV, so we have to be very careful in measuring them. I will try to measure this tomorrow.

[ginji]

P.S.
I tried adjusting the internal ASTIG, but it did not fix the problem.

[bdunham7]

P.S.
I tried adjusting the internal ASTIG, but it did not fix the problem.

Isn't it on the front panel??  And I don't expect it to fix the problem, but you should see a change in the focus as you adjust it.  At one extreme the letters will all be stretched vertically, the other horizontally.  See if it does that and if the effect is the same everywhere on the screen or not.

Is there a schematic for this model?  I'd be interested to know what feeds the horizontal and vertical final amplifiers.  Do you have another scope available?

I sort of doubt the issue is in the HV section, especially the post-deflection acceleration anode supply.  Do you have another scope available?  You'd want to start by looking at the actual voltages on the vertical deflection plates.

[ginji]

Thank you again for your very accurate comments.

I will try the ASTIG and other adjustments again.
I don't have a schematic for this model, so I don't know what they use for the final horizontal and vertical amplifiers. I will look for it on the board next time I disassemble this model.
I do have another oscilloscope, and I will try to find out what the voltage on the vertical deflector is.
It certainly may not be a problem with the acceleration anode voltage in the HV section.

[frantisek]

Get an SM and adjust or repair the cushion correction circuit.

[ginji]

If I had a service manual, the problem would be easy to solve. But the service manual was not to be found. This is why I am using this forum to ask for your wisdom.

[ginji]

I've tried adjusting ASTIG, trace rotation, and orthogonality, but it doesn't fix the problem.
I have removed the outer shell of this model, which contains the CRT, vertical and horizontal amplifiers, and the socket for the CRT, so I will measure the voltage at each pin in the future.

[james_s]

In many scopes the deflection plates connect via pins that come out of the side of the CRT neck, it's necessary to keep the connections as short as possible on high bandwidth scopes. If you remove the CRT completely you may be able to see enough of the electron gun to tell if it is damaged. If you have a curious enough doctor or veterinarian you may be able to get the tube x-rayed to get a better look.

[ginji]

The X and Y deflection terminals of the CTR were connected to the amplifier at the shortest distance from the side of the tube. I don't intend to disassemble the CRT part any further, and if it is a CRT failure, I will give up on repairing it. I hope the cause is not the CRT.

[ambrosia heart]

The X and Y deflection terminals of the CTR were connected to the amplifier at the shortest distance from the side of the tube. I don't intend to disassemble the CRT part any further, and if it is a CRT failure, I will give up on repairing it. I hope the cause is not the CRT.

There are 3 reasons causing your problem not ASTIG, FOUCS High voltage, or CRT BIAS
1. Magnet
2.CRT damage
3.Non Linearity of saw teeth waveform of horizontial board.
The high voltage board getting wrong does not show your symptom.
If you don‘t believe, replace high voltage board ALL coponents except the transformer.  I am sure problem exists still.  See photo. Cursor cannot be seen. I repalce 1  component to fix it, neither horizontal board , high voltage nor vertical board. Fixing CRO needs schematics. No schematics no talk. Even you got schematics, 90% cannot be fix.You can see 0.5V is higher in amplitude but cursor words still straight.
 11.JPG (44.41 kB. 800x600 - viewed 99 times.)

[ginji]

Mr.ambrosia heart

Thank you very much.
As you pointed out, I'm also suspicious of the sawtooth wave in the horizontal sweep. I'll check it out later.

[Chris56000]

Hi!

I think there's a lot of floundering in unnecessarily deep water here!

Distortion like that across the entire width of the CRT face is either caused by unwanted interaction between the X and Y deflection voltages due to defective smoothing or decoupling electrolytics on the h.t./l.t lines or a possible CRT fault, and the way to prove this is to short–circuit the Y deflection plates Y+ and Y– together with a 100 Ω 2W resistor.

If the horizontal line straightens out, there is interaction between the X and Y deflection voltages, but if the curvature is still as before there is a defect in the CRT itself, or the mineral shield has got magnetised!

A magnetised sheld can be degaussed very carefully with a hand–held degaussing coil but don't hold it too close to the shield (no less than 3" or about 75 mm away from it), and make sure you move the coil at least 12–18 inches from the CRT/shield assembly before you switch the degauss coil off!

Some more sophisticated Oscilloscope CRTs have an "interplate shield" or "expansion mesh" that can cause distort the trace like this if the voltage to it is not correctly set, but the CRT in the OP's Pintek isn't one of this type I'm afraid!

Chris Williams

[Wallace Gasiewicz]

Which of the scopes are we referring to here?

Ginji scope trace looks like Barrelling, (like Pincushoning) and there is usually an "orthogonality" (I think that is what it is called) adjustment for that on analog scopes.

Dhanusha's scope is an asymmetrical baseline and is different

[ginji]

Mr.Chris56000

Thank you for your support.
I have received various opinions on the cause of the problem from all of you, thank you, I will consider them carefully and investigate.

I don't have a schematic or service manual, so I'm referring to relevant documents and schematics of slightly older models for consideration.

It may be an abnormality in the vertical amplification circuit (+Y.-Y) as you pointed out.

We will proceed with caution so as not to damage the equipment by the investigation.