On the subject of plasma's....

[freakaftr8]

Hope you guys dont hate me for this, (starting plasma talk on the forum)..
But I have aquired this 42" Magnavox (Samsung guts) plasma. The Power supply had a blown voltage regulator IC for the Vscan circuit. I replaced it and a shorted zener diode in it's path. Now with Vscan restored it should normally operate at -190vdc. Im getting a whopping -305vdc and is not adjustable via the Vscan pot. I have checked the pot to make sure it is operating and it works. Any ideas? I am stumped.

Originally either the PS blew the y-sus and buffers or the buffer shorted, wreaked havoc on the sustain and then harmed the PS. Haven't gotten that far yet until I can restore the supply to norm operation.

[andy]

...

[radiotvnut]

I've seen the problem in many cheap later model CRT sets with switching power supplies and the problem is generally one of the things that's mentioned above. Unfortunately, the extremely elevated B+ voltages usually fries other circuits in the TV. Many times, to the point where the TV isn't worth fixing. I suspect the same can happen to a plasma or LCD TV.

[freakaftr8]

Absolutely. Im going to look at the optocoupler. I have seen these go bad. Good call guys! Thanks again

[Findm-Keepm]

Is this close to what you are working on?

Gateway, it seems is also made by Samsung, and they post some of the service manuals for Plasma sets on their website. A Google Search turned up this one:

http://support.gateway.com/s/Manuals...TW-P42M203.pdf


LG, I could help greatly. With Samsung, it's always been about dead sets and 35V electrolytics - 470, 680 and 820uf, along with any others that are obviously bad.

Cheers,

[peverett]

This is not related to the Plasma TV. but I attended a seminar given by a company trying to design a solar cell inverter that will last 25 years(the same as the solar cell panel life). They said that they avoided two things in their design:
Optocouplers and Electrolytic capacitors.

Sounds like optocouplers, like electrolytics, are trouble!

[andy]

...

[freakaftr8]

Which pins are the output on one optocoupler? The side with the dot denoting pins 1 and 2 or is it 3 and 4?

[freakaftr8]

Somehow as I was testing caps last night I ran across a small non polarized picofarad cap that read nothing on my meter. It was labeled 104. Well replaced it with a 102 now I still have unmanageable voltage but it's lower at -220vdc. And surges.

[andy]

...

[andy]

...

[freakaftr8]

thanks for te tip Andy! Guess im lucky I didn't smoke something

[freakaftr8]

Well Andy you were right! I shorted the two output pins on the opto and to my surprise the voltage dropped to roughly 1.2vdc. So the primart side is working. Since I have checked out the secondary side components minus the opto, im going to replace it. My question is the opto is labeled p421. I have some other plasma power supplies and im wondering if I can use it's optocoupler? Mine is tan colored and the others are black. They would be coming from the same principle on that board.

[andy]

...

[freakaftr8]

Ok will do. When I get the power supply back to spec guess I get to see what lovely damage it did to the Ysus and buffers. Well I aready know the buffers are done for. The upper one smells great!