Prima ps-42d8c no picture

[thecrazy]

Hi,

I have a Prima ps-42d8c plasma tv that powers on but has no picture.
I beleive it may be a problem with the main power board as I tested some voltages found on a sticker on the top right corner that was inside the tv and VS is giving me 35v instead of 87.

All the parts in the tv seem to be made by Samsung. On the power board it says B4K-50 (Code No.LJ44-00055A) REV 03

I tried googling around for a service manual or some trouble shooting tips but couldnt find much except some shady chineese manufacturer that claims to be selling replacement boards but I dont really trust those.

Im good with soldering and know how to use a multimeter but i dont know how to troubleshoot electronics when there is no parts that obviously needs to be replace (burned, or melted) so I would appreciate all the help you guys can give me.

Nothing seems damaged on the power board so I beleive repairing it may be a good option if i could figure out how to find which part to replace.

Fred.

edit: I have the exact same tv as the guy on that thread https://www.badcaps.net/forum/showthread.php?p=93294 His pictures are the exact same thing i have tough Im not ready to write it as been too old as I just had my first baby and the wife made it quite clear we were'nt going to buy a new tv anytime soon

[thecrazy]

Re: Prima ps-42d8c no picture

What I first did was measure the voltages on the headers on the left and right of the power board that i beleive are connected to the x and y board.

A sticker in the TV says VS should be 87 but i get 35v
VSET should be at 93 but i get 78.

Could someone with experience please help me figure out what to do/test next?

[Agent24]

Re: Prima ps-42d8c no picture

This may help: http://www.repairfaq.org/sam/smpsfaq.htm

"Symptoms: voltage has changed and adjustment pot if one exists has no effect or is unable to set voltage to proper value. Check components in the feedback regulator, particularly the opto-isolator and its associated circuitry. A weak opto-isolator may allow for excessive output voltage. A shorted photodiode in the opto-isolator may prevent startup. An open photodiode may lead to a runaway condition. WARNING: probe these circuits with care both because of the safety issues but also since any slip of the probe may lead to a runaway condition and catastrophic failure of the switchmode transistor and its related parts as well as damage to any attached equipment. "

[thecrazy]

Re: Prima ps-42d8c no picture

ouch, im out of my league, I think ill try ordering a replacement power board instead. Is there any way of making sure the X or Y board in the TV is in working order? I dont mind spending 100$ to repair the TV but more than that would be a waste.

[Agent24]

Re: Prima ps-42d8c no picture

No idea, guess you'll have to see if someone else replies with some more help. I don't know much about plasma TVs