TM202G..weird B+ issue..all over the place

MonsterBash

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After reading a bunch of post here..I had no idea these were such a POS.

So I capped a dead one and it came back to life...the problem is with the B+ measurement.

I was getting about 94~96VDC (123VDC required) at the B+ test point. I thought that was extremely low and probably not adjustable. After removing the glue from the B+ pot..whenever I try to adjust it it goes from one extremely to the other. Just moving the POT a CH clockwise will send it to 135VDC...if i continue with moving it same direction..it will drop to 92VDC. Almost like hitting the ends of the adjustable range..but nothing in the middle.

I OHMed out the POT and it seems correct.

Double checked the CAPs and polarity

I've tried a couple DMM with the same results. I've tried grounding directly to the ground stud on the transformer and the monitor chassis

The flyback did have a small crack in it that was fixed with silicon.

As for the picture..it looks fine..every once in a while I'll get a little pulse in the screen but once it's been on for a while (say 5 minutes) that seems to go away.

Right now I have the POT set were it was glued

I'd really like to keep using this monitor as it has almost a perfect tube. VERY little..if any burn
 
Almost like hitting the ends of the adjustable range..but nothing in the middle.

I OHMed out the POT and it seems correct.

So, you can turn the pot while measuring it and smoothly change the resistance? It's not uncommon to have a pot with a dead spot, or that only works in one small section - especially if it had glue on it.

If the pot itself is OK, I'd turn my attention to the voltage regulator transistor. Not sure which one it is on this monitor off the top of my head.

I'd really like to keep using this monitor as it has almost a perfect tube. VERY little..if any burn

The Matsushita monitors almost always have perfect, unburned tubes. That's because none of them ever worked long enough to get screen burn...

-Ian
 
Thanks Retro...

I'll take a look at the schematics for the voltage regulator transistor.

The POT has (what looked like) the factory gunk on it to keep it from turning.

An yes..when I rotate the POT while testing it's all over the place



So, you can turn the pot while measuring it and smoothly change the resistance? It's not uncommon to have a pot with a dead spot, or that only works in one small section - especially if it had glue on it.

If the pot itself is OK, I'd turn my attention to the voltage regulator transistor. Not sure which one it is on this monitor off the top of my head.



The Matsushita monitors almost always have perfect, unburned tubes. That's because none of them ever worked long enough to get screen burn...

-Ian
 
An yes..when I rotate the POT while testing it's all over the place

The voltage or the resistance of the pot? If the resistance of the pot jumps all over the place, then it's bad and has to be replaced. If the resistance of the pot changes smoothly and the voltage jumps all over the place, then it's something else.

-Ian
 
The POT is nice and smooth..it's the voltage that's wacky

The voltage or the resistance of the pot? If the resistance of the pot jumps all over the place, then it's bad and has to be replaced. If the resistance of the pot changes smoothly and the voltage jumps all over the place, then it's something else.

-Ian
 
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