Cause for CRT Monitor Jittering?

[sideburn]

Hey y’all, I’m back and revisiting this again. Same monitor. But the symptoms are now a little different. I never fixed it and it was put away for a coiled years. Now the horizontal is shifting on a slow vertical sweeping. I ruled out the a/c outlet / ground loop and the composite video input. Opened it up and caps physically look ok as well as solder connections and traces. No schematic and I can’t tell where to look on the board or what to try next. Can you look at my YouTube video and see if you have any suggestions?

Video here—> https://youtu.be/Qfw7dzLMNPo

[PKTKS]

by the age of such components ....

My first guess is really a bad cap unable to filter the signal....

This is old stuff  expect a lot of vintage components faulty

Today - unless you are vintage collector -  repairman hardly invest time on this stuff

no parts no support no schemas (they are all on printed services..)
(those service manuals at time costing a fortune... today they skyrocket..)

and no value for the money.

Unlesss it is yours and collectors stuff.. ( i have some vintage pet gizmos myself..)
Expect no money or support anywhere...

Paul

[sideburn]

Totally collector, hobby, repair. I fix old computers etc.. this is hooked to a repaired apple ][ and C64.
I assume its a cap but I'd rather not have to replace them all to find out. Would like to isolate down to a certain area. Just not sure which area. Maybe its A/C noise so the issue is in the power supply zone...

[Rasz]

You can try blowing cold/hot with a hair drier and watching for change in distortion

[Bud]

It is just screaming power supply capacitors problem.
They may look ok but you cant tell just by the look unless they leaked. They may have dried, not leaked.

[Ian.M]

Yes.  The slow rolling offset is caused by the beat frequency between your nom. 60Hz mains supply, which wanders by approx +/-0.05 Hz due to demand on your regional electricity supply grid and the SX64's crystal generated frame sync, again nom. 60Hz.  Something is taking the monitor's horizontal scan circuit out of spec for part of each mains cycle, and a dried out main reservoir capacitor in the power supply (causing excessive 2x line frequency ripple on its outputs) is a prime suspect.

Its a pity you didn't shoot the video with the whole screen in shot, and preferably with a grid pattern displayed.   If we saw two bands of distortion moving up or down, with each coming onto the screen before the other leaves the opposite edge, it would indicate 120Hz ripple, which is diagnostic of a non PFC PSU with a bad reservoir cap.  OTOH if it had a single band, that would indicate either 60Hz ripple possibly due to a bad diode in the mains rectification section of the PSU, or due to a ground loop causing a threshold shift in the line sync circuit.   I think we can rule out a bad degaussing circuit due to the good color purity and the sharp transitions between straight scan edges and where its distorted.

[sideburn]

You can try blowing cold/hot with a hair drier and watching for change in distortion

good idea, on the main PCB right?

[sideburn]

It is just screaming power supply capacitors problem.
They may look ok but you cant tell just by the look unless they leaked. They may have dried, not leaked.

would that be that big cap on the main board? trying to find out WHICH caps they are...

[sideburn]

Yes.  The slow rolling offset is caused by the beat frequency between your nom. 60Hz mains supply, which wanders by approx +/-0.05 Hz due to demand on your regional electricity supply grid and the SX64's crystal generated frame sync, again nom. 60Hz.  Something is taking the monitor's horizontal scan circuit out of spec for part of each mains cycle, and a dried out main reservoir capacitor in the power supply (causing excessive 2x line frequency ripple on its outputs) is a prime suspect.

Its a pity you didn't shoot the video with the whole screen in shot, and preferably with a grid pattern displayed.   If we saw two bands of distortion moving up or down, with each coming onto the screen before the other leaves the opposite edge, it would indicate 120Hz ripple, which is diagnostic of a non PFC PSU with a bad reservoir cap.  OTOH if it had a single band, that would indicate either 60Hz ripple possibly due to a bad diode in the mains rectification section of the PSU, or due to a ground loop causing a threshold shift in the line sync circuit.   I think we can rule out a bad degaussing circuit due to the good color purity and the sharp transitions between straight scan edges and where its distorted.

There is one spot in the video of the whole screen also i have shots of the PCB do you know where on the PCB I should be working based on the screenshot ? I will look it over some more for bridge rectifier/power circuit area 

[Bud]

It is just screaming power supply capacitors problem.
They may look ok but you cant tell just by the look unless they leaked. They may have dried, not leaked.

would that be that big cap on the main board? trying to find out WHICH caps they are...

Electrolythic capacitors dry out faster from heat. Look at capacitors located in close proximity (1-10mm) to a heat source, e.g. high power resistors, heatsinks.

[james_s]

Why don't you get an ESR meter and test them? I bought one back in the late 90s when it was almost $200, a lot of money back then but I was repairing quite a few CRT monitors and it was an indispensable tool. Now you can get them a lot cheaper, or build one yourself.

[sideburn]

Why don't you get an ESR meter and test them? I bought one back in the late 90s when it was almost $200, a lot of money back then but I was repairing quite a few CRT monitors and it was an indispensable tool. Now you can get them a lot cheaper, or build one yourself.

Pretty sure I have one. The problem is there's tons of caps on this board and I would have to remove them anyway to test them so at that point, might as well replace them anyway since they are so old.

[Jeff eelcr]

That has to do with the camera scan rate and the TV/monitors it takes special
equipment to make that go away.
Not the same as the power supply capacitors failing.
Jeff

[sideburn]

Hey All, I checked the caps on the board with an ESR meter and visual inspection again. I see no bulging and the ESR is showing them as ok.

Here is a full screen view video of the issue: https://youtu.be/_liYw2lJrPc

The horizontal line thats moving up the screen is not visible in real world so that must be a syncing issue with the camera. but you can see the shifting section on both the left and right edges of the screen. its like a 5" tall section is shifted to the right by a few "pixels"...

still trying to resolve this mystery.

[floobydust]

It looks like AC hum bars, you have mains frequency ripple. What 's the monitor's model number?
Hum bars are usually in the monitor's power supply on say a 130VDC rail if it's using mains rectified. Or your computer has hum in the video output and the monitor is fine.
Either way, it's likely a filter capacitor has failed low value.
The de-gaussing circuit not shutting off looks different, the entire screen wobbles.

[sideburn]

It looks like AC hum bars, you have mains frequency ripple. What 's the monitor's model number?
Hum bars are usually in the monitor's power supply on say a 130VDC rail if it's using mains rectified. Or your computer has hum in the video output and the monitor is fine.
Either way, it's likely a filter capacitor has failed low value.
The de-gaussing circuit not shutting off looks different, the entire screen wobbles.

It’s a Sony PVM—380. It’s definately the monitor and not the computer or my a/c outlet. I’ve ruled that out and connected multiple composite inputs from other devices in multiple locations.

I’ve attached a couple photos of the main board. Maybe you can see which caps I might want to have another look at and maybe swap out? I was wondering if it may be the big brown ceramic cap below the fuse and above the power cable on the bottom left. No idea what type it is or what its value is though...

[sideburn]

Looks like that cap is inline with the a/c main, the fuse and what looks like an inductor..?..

I have a cap in my parts bin form another monitor repair that looks similar.
Maybe I could piggy back that onto the board or swap it out if you think that may be the culprit?

[sideburn]

photos:

front/back


pub back


spare cap (this was for an arcade machine monitor chassis i never ended up using. Maybe it will work as a replacement?:

[Ian.M]

Nope.  That's a line filter cap across the line after the fuse.   If it was bad it would blow the fuse, and could never cause your symptoms, even if you dyked it out completely!

The odds are in excess of 99.9% that the fault is a bad ELECTROLYTIC cap in the PSU section. 

However there doesn't appear to be a switching transformer in the PSU, and from the PCB layout of that section, and the lack of an isolation gap anywhere except round the Video/Audio In section, its almost certainly got a live chassis, so extreme caution is required when working on it.  Unless formally qualified to do so, please don't attempt to make any measurements or otherwise handle it with the mains supply connected.   

I cant find any references to a "Sony PVM—380" monitor - please post a photo of the model and serial no. label so we can search for the exact model number and try to find you a schematic.

[andy2000]

The only part of the monitor that could introduce power line ripple is the power supply.  I'd start by replacing the caps near the 20W 200 ohm resistor.  They work hard, and are exposed to heat from the resistor and voltage regulator on the big heat sink. 

That monitor is based on a common for the era Sony 13" TV chassis without the tuner and IF components.  It uses a hot chassis with opto-isolators on the video input. 

[sideburn]

Nope.  That's a line filter cap across the line after the fuse.   If it was bad it would blow the fuse, and could never cause your symptoms, even if you dyked it out completely!

The odds are in excess of 99.9% that the fault is a bad ELECTROLYTIC cap in the PSU section. 

However there doesn't appear to be a switching transformer in the PSU, and from the PCB layout of that section, and the lack of an isolation gap anywhere except round the Video/Audio In section, its almost certainly got a live chassis, so extreme caution is required when working on it.  Unless formally qualified to do so, please don't attempt to make any measurements or otherwise handle it with the mains supply connected.   

I cant find any references to a "Sony PVM—380" monitor - please post a photo of the model and serial no. label so we can search for the exact model number and try to find you a schematic.

Ahh ok, thanks for clearing that up, and thanks for the caution, I've worked on many monitors and familiar with the KV's they put out so i try to be safe. Yeah I was unable to find schematics or any info...

I have attached photos of the back with the model and serial number:

SER. NO. 5004449
MODEL NO. PVM - 1380
MFG Date: MAY, 1987

[sideburn]

The only part of the monitor that could introduce power line ripple is the power supply.  I'd start by replacing the caps near the 20W 200 ohm resistor.  They work hard, and are exposed to heat from the resistor and voltage regulator on the big heat sink. 

That monitor is based on a common for the era Sony 13" TV chassis without the tuner and IF components.  It uses a hot chassis with opto-isolators on the video input.

I keep thinking it might be that big cap right above the 20W resistor. ESR says its good but maybe I should remove it, test again and replace it anyway.

[wasedadoc]

The power supply has a bridge rectifier so all its electrolytics are seeing twice the mains frequency. Your disturbance is at mains frequency, not twice it. First suspect would be an open circuit diode in the bridge rectifier.

[floobydust]

I don't find a service manual or schematic for the Sony PVM-1380. You have to find the chassis number SCC-___, as you can see the same board 1-614-793-22 may have also been used as a TV set. I checked and BVM-1310 broadcast 19" rack-mount is a different bird.

I've seen the hum bars as a problem with the 120VDC or maybe 130VDC rail, whatever comes out of IC601 - if you can give us that part number. The main filter cap being low value, OP you say the ESR is good but that is not capacitance value. C603 330uF and the little cap next to it would be suspect. Be very careful any stray charge there will bite.
I've also seen the hum from the NTC/degauss causing low input voltage to IC601.

edit: maybe look here https://archive.org/details/sonymonitors for monitors in the same family.

[sideburn]

ok i will have to pull the board back out and then I can get you the  IC601 PN.
I don't even see the bridge rectifier looking at the photos I took...