What causes monitors to expand and contract when going from extreme brightness change

Fusion916

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What causes monitors to expand and contract when going from extreme brightness change

I don't know what the correct term for this but I'm sure you guys know what I am talking about.

Some CRT monitors exhibits more than others and I'm sure its due to the age of some of the components on the chassis. I'm talking about for example white flashes on a black background causing the image on the screen to briefly expand and contract.

So what exactly is the right term for this and what causes this? Is a sync issue or something? Is it fixable?
 
I know what your talking about, but I also don't know what causes it. Sorry, good question though.

I have a 25" monitor that was hooked up to a Hantarex Polo chassis until I replaced the chassis with a newer different chassis. I can't remember the chassis brand until I go home to check, but I still get the effect you are talking about even with a brand new chassis although the tube and yoke are still original. Maybe the tube and or the yoke are suspects?
 
If you replace the chassis with a brand new one, yeah I guess the problem most likely is in the yoke (which sucks). Or maybe your new chassis is not a good quality chassis? Not sure.

Hopefully someone else can chime in with some more info or maybe at least what this effect is called so I can do some research on this.
 

Cool, that's the exact information I need. I see now it's due to poor voltage regulation. I now at least know what to check.

If I recall some of the basis schematics of a few different chassis, it looked like they pretty much all use discrete bipolar transistor based regulators after the rectified AC input. Is that usually the only regulated voltage or are the more post regulators for the RGB output?

It also says "Check the B+ to the horizontal deflection"

What does "B+" refer to? The power supplied to the horizontal deflection circuit?

Sorry, still new to crt terminology and repair but well versed in electronics in general.
 
B+ is the operating voltage of the chassis after regulation. It is different for various models (120vdc for G07, 108vdc for 20EZ, etc.)

As mentioned in that link, a dried out cap can cause this, and is the easiest and cheapest fix anyway, so I'd start with a cap kit before i go pulling transistors...
 
B+ is the operating voltage of the chassis after regulation. It is different for various models (120vdc for G07, 108vdc for 20EZ, etc.)

As mentioned in that link, a dried out cap can cause this, and is the easiest and cheapest fix anyway, so I'd start with a cap kit before i go pulling transistors...

Gotcha.

Thats actually the FIRST thing I was going to check. And planned on doing a cap kit anyway.

Also a bad filter cap after the rectifiers could cause poor regulation.
 
Ah, I remember now that I never could figure out how to set the B+ on that new chassis because there wasn't even a manual available, atleast in english. Maybe its finally out, I need to go check the brand tonight. It is possible that my B+ is not set properly and I never could figure out how to test it. There's probably five to six other knobs on the chassis that aren't labeled either so I was pretty SOL for settings when I got it.
 
eh.. as long as it isnt too awful bad i usually live with it.. i had a k7000 once that did id baad did caps and a flyback(due to crack) and after blooming was much much better
 
The new wei-ya chassis are bad about doing it, brand new. I think they're just not built as well (big surprise!)

Yep, I have a brand new one for a 19" tube here if anyone wants to buy it cheap. I tried hooking up to a mr. do in place of a 4900 chassis, and the blooming was really bad when you got the center and the screen changed to red. I would call it a significant change and was unacceptable. I fixed the 4900 and put it back in and now it is running great with no blooming.
 
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