K7xxx green screen of death

dlbagna

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In hopes of getting help, I figured I'd share my most recent experience with a problematic 25" K7191... With a P538 main board...

Problem
Intermittently, the monitor will start to over drive green, worst from left to right... See image links below... Sometimes cycling the power makes it go away. Most off the time not... One thing to note that when it's working, there is a thin green vertical line on the left edge of the screen regardless of the position of the image.

History...
Bought in dead condition... See thread Flyback Errupts! Reasons? (25K7191)... http://forums.arcade-museum.com/showthread.php?t=124185
Changed flyback, did cap kit... All was well... About a year later I did a tube swap with a TV tube... Reused the WG yoke... Again all was fine for about a year... Till the green screen of death.

What I've tried so far...
-Smalltownguy2 Rejuvenated the tube successfully with no faults... Green screen persisted..

-subbed in a neck board from a donor chassis I borrowed from smalltownguy2, same green screen

-moved my chassis to another 25" tube... Problem followed...

-tried swapping q1 with q2 to see if problem changed color... Nothing changed.

-changed q1, q2, q3 and their associated non polar caps and IC1 from smalltownguy2's working donor chassis. No change...

After studying Randy Fromm's trouble shooting flow chart I decide to check the B+ voltage for the heck of it which at that time I think it needs to be 123V... It measures 134.5V... So I figure I figure a bad voltage regulator a STR30130. By fluke I found one on a an old tv chassis that i had kept from a tube swap....

Anyhow... Swapped that in and changed C57 in case...

Fired it up and the B+ was now 130V... Still puzzled I looked up the regulator and it turns out it is meant to regulate at 130V... Matching the last digits of the part number STR30130... The 19" chassis uses STR3123 @ 123V. Monitor worked good for about a half hour, and the problem came back... Sorry for the tangential side note...

Pulling my hair our at this point... There isn't much in the green circuit that I haven't touched at this point.

Can Anyone help?

I've attached pictures of varying states.
Game Running
http://i868.photobucket.com/albums/ab248/dlbagna/game_runningMedium.jpg

No signal
http://i868.photobucket.com/albums/ab248/dlbagna/no_signalMedium.jpg

Red only test pattern
http://i868.photobucket.com/albums/ab248/dlbagna/red_onlyMedium.jpg

Green only test pattern
http://i868.photobucket.com/albums/ab248/dlbagna/green_onlyMedium.jpg

Blue only test pattern
http://i868.photobucket.com/albums/ab248/dlbagna/blue_onlyMedium.jpg

All colors test pattern
http://i868.photobucket.com/albums/ab248/dlbagna/test_pattern_RGBMedium.jpg

Final Note… moved all original components to the donor chassis (minus the voltage regulator) and it works fine… also tried to use a different video source...

Thanks...
 
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Have you experienced this green screen issue with another game hooked up to this chassis? Like the Cabal test rig you have, or the Pac-Man video feed?

You do still have the monitor extension cables I left you...maybe we should rule out your existing game rig.
 
Yep... tried the old Cabal rig and the problem persists...

(By the way... Nice hat...)
 
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I personally think you've got a trace somewhere that's close enough that it's shorting out against something next to it intermittantly. It'd be on the main board since you already tried the different neckboard.
 
Could be heat related. Try bringing the chassis into the cold garage and running it there. Then direct heat at the pcb with a heat gun. See if you can trigger the problem.

Or cool the board with freeze spray when it's wigging out to see if it clears up.
 
Thanks for the feedback...

I've tried to find any shorts, but I'll give it another look...

I also like the idea of the spray freeze... I have a can, unfortunately I couldn't get it to act up tonight... I'll try again tomorrow.
 
The Voltage Regulator that is and was in my monitor is the STR30130.

What tried to, but failed to communicate well is that there are two versions of K7XXX main PC boards. One with the main board labeled P447 and the other with P538.

P538 Configuration (which is what my monitor has)
STR30130 – 130V Regulator

P447 Configuration
STR3123 – 123V Regulator

All the documentation (Service Manual and Randy Fromm flow chart) that I have found are for the P447. So I just wanted to point that out for someone else who has a chassis like mine and who is measuring B+ Voltage.

My B+ is now dead nuts at 130V
 
The Voltage Regulator that is and was in my monitor is the STR30130.

What tried to, but failed to communicate well is that there are two versions of K7XXX main PC boards. One with the main board labeled P447 and the other with P538.

P538 Configuration (which is what my monitor has)
STR30130 – 130V Regulator

P447 Configuration
STR3123 – 123V Regulator

All the documentation (Service Manual and Randy Fromm flow chart) that I have found are for the P447. So I just wanted to point that out for someone else who has a chassis like mine and who is measuring B+ Voltage.

My B+ is now dead nuts at 130V

Just wrapped my head around this - I had no idea of the two revisions. Thanks for clarifying that.

Is the P538 only the 25" and the P447 only the 19" or are they found in both?
 
wells used 4 different regulators.



STR 30123
STR 3123

are used in the 9', 13", 19" and all share the P447 main board.



STR 30130
STR 3130

are used in the 25", and 27" and share the P538 main board.


Peace
Buffett
 
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