Really Odd 25k7000 Issue

Peale

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took in a 25K7000 for repair. All original caps and fly. Original complaint was about pincushion and other picture issues.

This is P538 chassis, with the pincushion board.

On initial exam the flyback was cracked, and several of the caps were bulging. I didn't even bother with an initial test, I dove right into caps/fly.

On power up I noted that the top 1/2 of the screen appeared to be perfect, while the bottom was only drawing one scanline every centimeter or so.

I twiggled and twiggled and suddenly...I had a perfect picture. Very odd. So, I kept twiggling...and suddenly I had vertical collapse!

Convinced that I had blown the vertical IC, I ordered a couple of replacements. While I was waiting (for the LA7833) I did find one on a TV chassis. Once I replaced it, I turned all of the pots to their lowest setting, and powered it up. bringing up the screen control I could see that I had a very small picture of some kind, and once I started to make adjustments, I was back to where I started with the 1/2 top good, 1/2 bottom spaced.

And then...poof...vertical collapse, again.

I stood there for a few seconds, then turned the vertical sync back a notch, and *poof* it came back.

With more adjusting, I had a perfect picture. It's running like that, right now, with a Klax board. I know it's not fixed by any stretch. Any ideas? I've never heard of selective vertical collapse.
 
And now that it's been running for a bit, I can't get the problem to repeat itself.

I've tried a bunch of different boards, and they all look perfect.

Which leads me to believe that it's a bad cap, but I /just/ replaced them. All of them.

So...bad cap, right out of the box, but which?
 
How about broken trace or leg somewhere that you haven't caught yet?
 
Anything is possible. The longer it ran, the better looking it got. I'm going to let it cool down for a few hours, and try again.
 
i chased one like that once.

it was a broken vertical pot.

it had broke so that if you did not flex the pot back into the chassis with your fingers you would have never seen that it was broke.

after that it ran just fine.

Peace
Buffett
 
I just got an email from the owner. It's been hooked to a 27" tube. That certainly explains the pincushion.

What are the differences between the 25" and the 27" K7000s?
 
from what i know there is not much difference other than the add on boards that hook to the expansion port that are on the 27" models and a resister or two added on to the main chassis underside.

all undocumented of course.

other than that i cant see much difference in them.

Peace
Buffett
 
After a night to cool down, I fired it up...and it came up with no issues.

I twiggled and beat on the pots to try and get the problem to repeat, to no avail. I didn't think it was a pot issue anyway, as they adjusted just fine.

I could get it to /almost/ screw up by cranking everything to it's max, but it never did.

And, I found that this isn't even married to the tube on which it's been mated. It's a DDR machine, so it originally had some oddball chassis.
 
Fired it up this morning...totally screwed.

But, I did find out why. Broken H HOLD pot. Start wiggling THAT one around, and *presto* the issue comes and goes.
 
1.00 each. + shipping.

i want to get my site looking better but i don't know how to do web stuff.:(

PM me with what you want or need i stock most all K7000 Parts.

Peace
Buffett
 
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