Jitter on locked horizontal part of image - B&W transistorized TEC monitor

I have an older monitor from a video game - and it has a jitter on the horizontal lines on the screen (vertical is locked), yet I don't see this jitter on the H Sync. Using a signal generator (Cross-Hatch, Dot, etc.) and all outputs are the same. Game source also shows same jitter on same screen.

It is not the WICO monitor signal generator as other B&W monitors show a locked image.

Schematics here:

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Monitor has been recapped. Horizontal does lock, but jitter still present.

Suggestions appreciated!

Thanks,

John :-#)#

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Reply to
John Robertson
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Sounds like the power supply is starting to fail. Check the caps there, for bulging ca[p tops, and replace them. While it is open, also check around the high voltage area, and if you smell ozone, something is producing sparks. Clean and replace bad caps.

Reply to
Sjouke Burry

You said it "has a jitter on the horizontal lines on the screen (vertical is locked)". Just want to be clear. Do you mean to say the horizontal lines from the generator are jittering up and down indicating a vertical problem?

Reply to
ohger1s

The monitor has had all electrolytic capacitors replaced, along with most of the mylar ones.

We use Panasonic caps for electrolytics.

No, the lines are jittering sideways - indicating a horizontal problem. If I adjust the horizontal control the jittering stays much the same as the picture shifts sideways until it loses the lock.

John :-#(#

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Reply to
John Robertson

I wonder if you're describing what we used to call "piecrusting". Most of that was was from leaking HV. Remove the HV rectifier and see if there's any green schmutz in the contacts. Any corrosion will cause arcing.

Reply to
ohger1s

If the problem isn't HV arcing, check or replace parts from pin3 of the flyback including the 2 AFC diodes D401 and 402. The diodes on this line I'd just replace.

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Reply to
Chuck

A dry joint is also possible, or a noisy part burned resistor dropping feedback from a flyback winding to the phase discriminator.

Arcing usually isn't too hard to see - corona discharge can be, a faint purple haze around any sharp pointy bit at EHT potential. Sometimes you have to view the chassis with the light turned off to see it.

Reply to
Benderthe.evilrobot

Sorry, been busy. The diode is soldered directly to the HV leads. So a bad connection is out. The HV probe does not show any obvious signs of jitter, but I suspect that would be the case seeing as the tube is a giant capacitor and would smooth over most noise.

I also pulled the LOPT/Flyback and did both a ring test and a leakage test - it passed both just fine, good ring count, and no appreciable leakage using my old Heathkit R/L/C Bridge Cap checker (1960s - with Magic Eye tube!).

Additional comments in response to other posts on this topic...

Thanks,

John :-#)#

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Reply to
John Robertson

Hi Chuck,

Thanks for the suggestions - I tried all that and no improvement in the image quality. I used a couple of 1N43 Germanium diodes in place of the AA143s, but (as I said) no change.

The only place I can 'see' a problem is when I monitor the cathode of the picture tube. The horizontal section appears quite stable with no flicker showing on my fast Tectronics scope.

Images:

Video - jitter on screen:

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Scope - base of Horizontal drive:

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Scope - base of final video amp:

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Schematic - base of final video amp (wrong version of schematic here though):

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Appreciate any other suggestions. I haven't yet tried replacing the resistors in the feedback loop, however the jitter doesn't show in the loop...

Thanks!

John :-#)#

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John Robertson

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