Oscilloscope horizontal line is curved. How fix this? - Page 1
Forum section: electronics / repair

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 24, 2019, 06:18:57 pm
content: My analog oscilloscope is a PINTEK PS-350 one. Now the horizontal line (ground line) of that is slightly curved. Due to this reason, now the edges (rising and falling) of the calibration square wave signal also have slight slopes. Every time/div have same slope. This is not a problem of probe compensation or trace rotation. I checked them. The calibration signal is correct. Also I have checked that. I expect a solution for this. Thank you.

author: james_s
author_rank: Super Contributor
timestamp: March 24, 2019, 06:24:18 pm
content: It's very difficult to say for sure without doing some tests, but often this is the result of internal damage to the CRT. Can you try swapping the horizontal and vertical wires to the deflection plates? That should result in a vertical trace instead of horizontal but if the trace is still curved then the problem is probably not with the CRT.

author: jdragoset
author_rank: Frequent Contributor
timestamp: March 25, 2019, 01:01:52 am
content: Since it is not time/div related, almost seems like unwanted magnetization of CRT components or shield.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 25, 2019, 03:18:32 am
content: Thanks jdragoset.Can you tell me that is there a way to demagnetize that components?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 25, 2019, 05:49:14 am
content: With persistence and luck you can compensate for the magnetised parts with another magnet in the appropriate position. The problem is finding said magnet and position. Watch the screen while moving magnets around and use that as guidance.Obviously this means putting your hand (the old high voltage rule is one hand at a time) near high voltage circuits while they are operating. Be very careful.The second problem is fixing the compensating magnet in position, and the possibility that the situation will drift over time. Sometimes it is just best to move on to another scope.

author: james_s
author_rank: Super Contributor
timestamp: March 25, 2019, 06:36:12 am
content: Wouldn't it be easier to use a degaussing coil to demagnetize rather than try to compensate for magenrised parts? Of course it it turns out to be internal damage to the CRT then compensating may be the only option.

author: tautech
author_rank: Super Contributor
timestamp: March 25, 2019, 07:07:50 am
content: Quote from: Dhanushka on March 24, 2019, 06:18:57 pmEmail Pintek for the service manual.pintek@pintek.com.twUser manual:http://www.pintek.com.tw/pdf/Analog_Oscilloscope_0224.pdf

author: jdragoset
author_rank: Frequent Contributor
timestamp: March 26, 2019, 01:24:28 am
content: Many Degauss coils are on ebay.That being said, Maybe a tool demag would be better if there are any magnetized higher carbon steel causing the problem.Degauss coils generate low AC magnetic field that work on soft iron (shadow mask, deflection plates, grid supports, cathode assembly and maybe the mu-metal shield) at some distance.Tool demag devices generate very strong AC magnetic field that work close-distance with a death grip until the tool is moved away and the field shut off.For most of these, the on time is only allowed for ten seconds to avoid over heating.We used to make a simple version with the coil from a two pole shaded pole fan motor, disconnected from the dovetail joints connecting it to the armature/shaded pole assembly.Bear in mind this drastically decreases the AC impedance and will rapidly over heat.Also the near-pole magnetic field will be very strong and should be isolated with 1/2' wood thickness.Energize near the demag target, move away slowly and energize.

author: jdragoset
author_rank: Frequent Contributor
timestamp: March 26, 2019, 02:11:05 am
content: Last line should read:Energize near the demag target, move away slowly and de-energize.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 27, 2019, 03:47:10 am
content: Thanks for all comments.Can you you tell me how make a DIY degassing coil using a degassing coil of a computer monitor? I have old 14" CRT PC monitor. I meant that what are the parameters such as diameter, voltage, current limiting resistor value etc. that suitable for 6" oscilloscope CRT. Also using these coils, can it be caused to make a problem?Thank you.

author: james_s
author_rank: Super Contributor
timestamp: March 27, 2019, 03:45:42 pm
content: Careful about tearing apart a 14" Pc monitor, those are becoming collectible. For degaussing the specs are not critical at all. I've used a 100W incandescent bulb as a current limiter for a degaussing coil from an old TV. I doubled the coil up a couple times so it was a loop about 4" diameter.

author: GreyWoolfe
author_rank: Unknown
timestamp: March 27, 2019, 03:57:29 pm
content: I was shown how to use a Weller soldering gun as a degaussing tool.

author: jfphp
author_rank: Regular Contributor
timestamp: March 27, 2019, 05:26:56 pm
content: On some old analog scopes there was a trimmer to adjust the "cushion" : a rectangular pattern had to be adjusted without been neither crunched nor inflated. Found on some digital CRT like Spectrum analyzer or network analyzers. The rectangular pattern is internaly generated with a lot of adjustement patterns. Magetizing of the CRT is not common with a mumetal shield found in almost every scope.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 28, 2019, 03:47:34 am
content: Thanks for all new comments.I am going to degassing my oscilloscope CRT using a 4" DIY degassing coil. Could you please tell me whether there is how much probability to damage my oscilloscope. I have attached a image of the calibration signal.Thank you.

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2019, 04:26:47 am
content: It's hard to tell for sure, but that looks to me like the trace rotation just needs to be adjusted, or possibly the circuit powering the rotation coil is not functioning. Is there a setting for that? Often it's a small recessed trimmer.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 28, 2019, 04:54:18 am
content: Thanks james_s.When I turn the trace rotation for straight the vertical lines the ground horizontal line get a an angle with X axis. Also, ground horizontal line is curved little.Thank you.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 28, 2019, 05:33:21 am
content: When I contact PINTEK, They says that the attached one should be used to demagnetize. Compared with this and DIY one, may DIY one have a probability to damage the CRT?Thank you.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 30, 2019, 06:47:33 am
content: I used a DIY 4" degassing coil in series with 100W bulb but the problem is not solved yet. PINTEK sent me the attached adjustments details, troubleshooting manuals and circuit diagram. Could you please send me a solution for this using that documents.Thanks.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 30, 2019, 06:48:56 am
content: Other documents

author: tautech
author_rank: Super Contributor
timestamp: March 30, 2019, 07:21:47 am
content: Quote from: Dhanushka on March 30, 2019, 06:47:33 amCircuit diagram, please post it.

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 30, 2019, 08:05:23 am
content: Circuit diagram

author: tautech
author_rank: Super Contributor
timestamp: March 30, 2019, 09:07:26 am
content: Quote from: Dhanushka on March 30, 2019, 08:05:23 amNow you have enough info to start from the basics and check all voltages in the PSU are OK and ripple is reasonable.There is no ripple spec but for all the low voltages it should be less than 20 mV. The 140V rail shouldn't be much more.Can you safely measure the EHT ? It could be -2000V !This might help understand all the things you need to check:http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: Dhanushka
author_rank: Regular Contributor
timestamp: March 30, 2019, 11:06:18 am
content: Thanks tautech.I do not have voltmeter to measure the 2000 V now. But can I use a florescent (taking that close to high voltage line) bulb to check that qualitatively?Thanks.

author: ginji
author_rank: Contributor
timestamp: January 30, 2022, 02:46:56 am
content: 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!

author: james_s
author_rank: Super Contributor
timestamp: January 30, 2022, 08:00:36 am
content: Probably internal damage to the CRT. Bent deflection plates or broken support inside the neck of the tube. It's also possible I suppose that something is magnetized.

author: ginji
author_rank: Contributor
timestamp: January 30, 2022, 08:36:24 am
content: 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.

author: ambrosia heart
author_rank: Regular Contributor
timestamp: January 30, 2022, 10:33:39 am
content: Quote from: ginji on January 30, 2022, 02:46:56 amCRT 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

author: ginji
author_rank: Contributor
timestamp: January 30, 2022, 10:49:14 am
content: 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.

author: ginji
author_rank: Contributor
timestamp: January 30, 2022, 11:18:22 am
content: 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?

author: ambrosia heart
author_rank: Regular Contributor
timestamp: January 30, 2022, 12:21:03 pm
content: Quote from: ginji on January 30, 2022, 11:18:22 amsee 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.

author: jonpaul
author_rank: Super Contributor
timestamp: January 30, 2022, 01:04:08 pm
content: 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

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 30, 2022, 02:08:06 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: January 30, 2022, 02:50:22 pm
content: See if the adjustment marked ASTIG has any effect on that.

author: ginji
author_rank: Contributor
timestamp: January 30, 2022, 08:25:45 pm
content: 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.

author: ginji
author_rank: Contributor
timestamp: January 30, 2022, 08:57:45 pm
content: I will disassemble the oscilloscope to see if this CRT has a trace rotation coil.

author: bdunham7
author_rank: Super Contributor
timestamp: January 31, 2022, 04:20:43 am
content: 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.

author: ginji
author_rank: Contributor
timestamp: January 31, 2022, 04:51:05 am
content: Mr. bdunham7Thank 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.

author: ginji
author_rank: Contributor
timestamp: January 31, 2022, 05:20:56 am
content: P.S.I tried adjusting the internal ASTIG, but it did not fix the problem.

author: bdunham7
author_rank: Super Contributor
timestamp: January 31, 2022, 05:39:30 am
content: Quote from: ginji on January 31, 2022, 05:20:56 amIsn'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.

author: ginji
author_rank: Contributor
timestamp: January 31, 2022, 05:56:18 am
content: 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.

author: frantisek
author_rank: Regular Contributor
timestamp: January 31, 2022, 04:17:19 pm
content: Get an SM and adjust or repair the cushion correction circuit.

author: ginji
author_rank: Contributor
timestamp: January 31, 2022, 10:25:50 pm
content: 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.

author: ginji
author_rank: Contributor
timestamp: February 01, 2022, 06:03:43 am
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2022, 06:19:25 am
content: 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.

author: ginji
author_rank: Contributor
timestamp: February 01, 2022, 06:32:28 am
content: 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.

author: ambrosia heart
author_rank: Regular Contributor
timestamp: February 01, 2022, 07:46:35 am
content: Quote from: ginji on February 01, 2022, 06:32:28 amThere are 3 reasons causing your problem not ASTIG, FOUCS High voltage, or CRT BIAS1. Magnet2.CRT damage3.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 121 times.)

author: ginji
author_rank: Contributor
timestamp: February 01, 2022, 08:32:53 am
content: Mr.ambrosia heartThank 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.

author: Chris56000
author_rank: Frequent Contributor
timestamp: February 01, 2022, 05:38:06 pm
content: 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

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 01, 2022, 10:34:13 pm
content: 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

author: ginji
author_rank: Contributor
timestamp: February 01, 2022, 10:37:13 pm
content: Mr.Chris56000Thank 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.

author: Andycap
author_rank: Newbie
timestamp: February 04, 2022, 12:15:32 pm
content: I have seen this before when the deflection coil has slid back along the tube neck. (From TV repair days but worth a check)

author: Gyro
author_rank: Super Contributor
timestamp: February 04, 2022, 01:07:17 pm
content: Unfortunately oscilloscopes CRTs are electrostatic deflection, not magnetic.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 04, 2022, 03:18:27 pm
content: Yes they are mostly electrostatic but some CRTs in scopes have magnetic yokes also.

author: bdunham7
author_rank: Super Contributor
timestamp: February 04, 2022, 05:45:08 pm
content: Quote from: Wallace Gasiewicz on February 04, 2022, 03:18:27 pmThat's a bit confusing...A CRO--a standard scope that displays the signal on a high-speed CRT in the conventional manner--typically has a trace rotation adjustment coil and everything else is internal and electrostatic.Some DSOs with a CRT display may use a small television-like CRT tube with magnetic deflection.Both of the scopes in this thread are of the former variety.

author: floobydust
author_rank: Super Contributor
timestamp: February 04, 2022, 08:42:53 pm
content: I don't understand the notion of damaged CRT's as if people are throwing oscilloscopes on the floor or playing football with them. Wouldn't that also break their glass? They do have G-force ratings, electron guns I've never seen "bent" inside without other consequences like broken PC boards or enclosure.I think warped deflection can also be caused by other things:Magnetized CRT or mounting frame, or trace rotation needs cal or its circuit is not working. This is usually a tilted trace.Problems with the deflection power supply, I've seen bad electrolytics cause it to have ripple or poor regulation. This is non-linear distortion in both H and V deflection.OP's square wave had brightness dots on the rising & falling edges, which means trouble in the form of power supply ripple. You can hetrodyne this at certain sweep speeds to measure it lol, but almost always means bad electrolytics capacitors in the power supply.The Iwatsu SS-6421 though looks non-linear like pincushion distortion, like a ball but it's electrostatic deflection. Tons of calibration menus too so "soft" cal must be stored somewhere. On the pc boards there's trace rotation (horizontal) , R195 ORTHO (vertical), R63 QUICIC Centering, R52 MAG Centering etc. This is not a scope for the faint-hearted. First try the S/W calibration, see if it got erased or a battery is dead. You'd have to run the service manual through a translate program:https://www.iti.iwatsu.co.jp/manual/pdf_j/analog_osc/ss-6421_6521-cal-j-t-change.pdfhttps://www.iti.iwatsu.co.jp/manual/pdf_j/analog_osc/ss-6421_6521-oj-t.pdf

author: bdunham7
author_rank: Super Contributor
timestamp: February 04, 2022, 10:26:24 pm
content: Quote from: floobydust on February 04, 2022, 08:42:53 pmIt certainly does happen, and often the glass does break internally but not the envelope. Just look at the video in the thread with the 2235. I agree that it probably hasn't happened here.QuoteMy thoughts as well. He needs to get another scope on the deflection plates and the amplifier supply, which I'm going to guess they share.QuoteOP is in Japan, so that probably will be of great help.

author: james_s
author_rank: Super Contributor
timestamp: February 04, 2022, 11:42:33 pm
content: Quote from: floobydust on February 04, 2022, 08:42:53 pmIt can happen fairly easily due to shipping damage, or if the scope is stored sitting on end and gets knocked over. The glass is quite strong and the internal structure of the electron gun is fragile. the deflection plates are often supported only on one end and then stick out into space, a good whack can bend one or break one of the glass rods that holds the whole structure together. I have seen scope tubes with internal damage that were still intact more than once.Color raster CRTs are easily damaged too, a good whack can move or distort the shadow mask causing a permanent purity error (colored blotch), I've seen that multiple times too.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 05, 2022, 12:34:14 pm
content: Concerning Yokes on electrostatic CRTs.There are some tubes that are electrostatic that also have coils on the tube to adjust the trace.I would refer you to this HP publicationhttp://hparchive.com/Manuals/HP-143A-Manual-SNP_925.pdfGo to Page 19 / 51: Page 4-4 of HP manualQuote:The TRACE Align Coil, L1and the ORTHAGONALITY coil, L2 are located under the CRT shield and control the alignment of the trace within the graticuleThese are adjustable with pots.I realize this is an old HP scope and not the scopes we are discussing and I really do not know if the scopes at question here have these coils.This is an O Scope CRT electrostatic tube type scope and not the TV tube display type scope.But these adjustment coils are fairly common.I think the Orthagonality adjustment is sometimes called Geometry adjust.Orthagonality controls the Pincushioning.

author: Gyro
author_rank: Super Contributor
timestamp: February 05, 2022, 01:04:24 pm
content: The spot welds within the gun assembly can be quite fragile too, particularly if you hit some kind of resonance during shipping. I once had a Tek scope where the first grid connection weld had failed where it joined the wire that comes through the base seal. Extremely frustrating to look through the glass and see a tiny fraction of a millimetre gap with absolutely no way of getting to it!

author: bdunham7
author_rank: Super Contributor
timestamp: February 05, 2022, 03:43:03 pm
content: Quote from: Wallace Gasiewicz on February 05, 2022, 12:34:14 pmThat's an interesting find! It is a rather unusual hybrid CRT and fairly low bandwidth (unless you get a sampling plug-in). I'm guessing that there were other old low-BW large screen scopes that were similar, but I haven't worked on them. The difference is that it is wide-screen and needs a lot of expansion to operate--and that is where the geometry issues crop up and the various coils are used. There is a picture of the CRT in the manual so you can see the TV-like shape of it. I suppose you could make a television tube with electrostatic deflection too...and they did!QuoteOrthagonality on things that have it is just trace alignment (rotation) in the vertical direction. Instead of one trace rotation adjustment that is more typical, you have trace rotation that you set the horizontal trace with and then you make a separate tweak to orthagonality (literally "right-angledness") to a vertical trace. Pincushion/Barreling is a separate issue and the HP143A you show has that as well. The (Iwatsu) OP's scope does resemble a barreling issue, so perhaps his is an unusual example of a small-screen high-BW CRT that nonetheless has those adjustments. If so, given his description of the problem, that circuit may have failed entirely.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 05, 2022, 08:15:15 pm
content: My HP 1980 scope has an adjust for the pincushion effectHas a pretty large screen also

author: ginji
author_rank: Contributor
timestamp: February 06, 2022, 12:03:41 am
content: Hello everyone.The following instructions are for handling and calibration procedures, which I have already obtained, but the contents of these instructions are not sufficient to solve this problem. Unfortunately, the service manual does not seem to be available.https://www.iti.iwatsu.co.jp/manual/pdf_j/analog_osc/ss-6421_6521-cal-j-t-change.pdfhttps://www.iti.iwatsu.co.jp/manual/pdf_j/analog_osc/ss-6421_6521-oj-t.pdfThe CRT of the IWATSU SS-6421 is of course electrostatically deflected and has TRACE ROTATION COIL and ORTHOGONALITY COIL.This problem could not be solved by these TRACE ROTATION and ORTHOGONALITY adjustments.We do not have a service manual for the SS-6421, but we are examining the schematics with reference to service manuals for other models.

author: m k
author_rank: Super Contributor
timestamp: February 06, 2022, 01:45:35 pm
content: My first impression from first picture was that deflection is so off that it's turning back.Obviously not the case here.

author: G7PSK
author_rank: Super Contributor
timestamp: February 06, 2022, 05:17:15 pm
content: When I was repairing watches they were degaussed using a capacitor discharging through a coil, not sure what size the capacitor was as it was inside a sealed unit but big enough to make a loud noise and the watch to jump when the button was pressed.

author: CaptDon
author_rank: Super Contributor
timestamp: February 06, 2022, 06:10:44 pm
content: A capacitor discharging through a coil causing the watch to jump would magnetize the hell out of it, not demagnetize it. De-magnetizing uses an alternating current field that slowly decreases to zero (or the alternating field is slowly moved away from the device).

author: CaptDon
author_rank: Super Contributor
timestamp: February 06, 2022, 06:22:40 pm
content: I had a PPI display which used a 5CP7A crt. One day when I powered the unit on the trace was of center (low and to the left) but slowly came back to nearly correct positioning. Being low and left indicated some negative Vertical and Horizontal ailment. I went crazy checking all kinds of things to no avail. I finally shorted the V and H deflection plates together, all 4 to one common short. Guess what, from a cold start after being powered off for an hour or two I was still seeing the exact same problem!!! How could that be with no differential on the deflection plates??? Turns out Broken gun support inside the C.R.T back at the cathode/grid 1 area!!! 5CP7 was a poor substitute for the 'A' version (crappy focus, crappy astig) but a 5ADP7A worked great after much adjusting. Twisted the base off the bad C.R.T. and crunched the glass nipple. Didn't want anyone to get hurt with a possible implosion. I hear these old 5" scope C.R.T.'s are pretty violent when the go boom.

author: thinkfat
author_rank: Unknown
timestamp: February 06, 2022, 06:33:08 pm
content: Quote from: CaptDon on February 06, 2022, 06:10:44 pmBut that is exactly what will happen in this case. Coil and capacitor form a tank circuit. The discharge through the coil will cause a dampened oscillation until the energy has turned into heat.

author: CaptDon
author_rank: Super Contributor
timestamp: February 06, 2022, 06:53:03 pm
content: Hmmm, sounds kind of brutal? I would have though the initial magnetic field would either damage the internals or produce a polar field so strong that even the decaying alternating field couldn't degauss it. I like the part "Made the watch jump", not on my watch!! I have had to de-mag my older watches using a bulk tape eraser. Sadly I used work around magnetrons, klystrons and crossed field amplifiers as well as more recently the systems with waveguide circulators all of which will put a hurting on a mechanical watch. Some of the old multi-megawatt magnetron magnets when separated from each other can lift hundreds of pounds of salvage out of the water. Those dead maggies were highly sought after!!!

author: ginji
author_rank: Contributor
timestamp: February 17, 2022, 03:49:19 am
content: Hello everyone.I have solved the problem.I measured the voltage at the CRT and pin number 7 is 0 volts.Pin number 7 is labeled B1, but it is probably IS or ISD.(IS:Insulation Shield).I removed the circuit board and traced the circuit one by one, and found that the 820KΩ resistor in the high voltage power supply circuit was broken.After replacing the resistor, the voltage on pin number 7 went up to 950 volts.For reference, below is the voltage of the CRT under normal conditions.Pin number 1: (H), 2: (K) = -2500V, 3: (G1) = -2500 V, 4: (NC), 5: (Q1-) = -480V, 6: (P2) = 40 V, 7: (B1) = 950 V,8: (Q1,2+) = 586V, 9: (Q2-) = -380V, 10: (Q3-) = -160V, 11: (G2) = 40V, 12: (?) = 5V, 13: (B2) = -710V, 14: (H)Thank you very much.

author: Pyral
author_rank: Contributor
timestamp: February 17, 2022, 04:21:11 am
content: Unfortunately I have experience with internal damage on CRTs, and that isn't it. The CRT damage looks like what happens when you try drawing a straight line over a rough surface. The line will be straight, then when it reaches a wrinkle in the shadow mask it will follow the crease until the actual beam pattern gets far enough away to go back to the expected path.Here is a video of what internal damage looks like.If you suspect internal damage, set your scope so that the beam is as wide and unfocused as possible so it takes up most of the screen. I forget what settings I used but I managed to get the whole screen illuminated. If its damaged it will be obvious because the crease will be visible instead of a uniform color.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2022, 04:28:37 am
content: Quote from: ginji on February 17, 2022, 03:49:19 amExcellent work. Thanks for posting the solution.

author: ginji
author_rank: Contributor
timestamp: February 17, 2022, 05:09:37 am
content: In the internal structure of the CRT, the IS（or ISD） is located between the X and Y deflections, and it is also responsible for correcting distortions.I did a lot of research on the structure of CRTs and found very few references to IS, and only one reference to it, which indicated that the cause of the problem was most likely related to IS.I spent a lot of time researching and thinking about the problem, as there were very few cases of oscilloscope bright line curves.Now I can use this classic analog oscilloscope (IWATSU SS-6421) again for a while.Thanks, 73!

author: m k
author_rank: Super Contributor
timestamp: February 17, 2022, 04:30:59 pm
content: Your problem is not very regular so google style(dominance) search is pretty useless.And you must find exact wording those others have used.I have used approach where I've concentrated to least significant google hits with long list of excluded words.Picture search is also many times better but then you have to guess what picture leads forward.