Samsung Plasma Tv not power on PS43D450A2

[phlox]

Hi all. I recently got a samsung 43" plasma Tv to diagnose
Model : PS43D450A2

The TV tries to power on. The relay clicks, then goes off . It does that about 3 to 4 times then switches off and the red panel light starts flashing. About 2 quick flashes every 2 or 3 seconds.

I also dont measure any voltage inside. Inside the TV theres a sticker to 3 voltages and on the power supply there are the 3 test points but dont get any voltage. It might show a high voltage for a second or so then goes off.

If i unplug either the Plasma driver boards or main logic board the the relay clicks once and stays on but also no voltage on the test points and no display offcourse.
There is phisically no sign of blown components and or bulging or leaking capacitors on any of the boards.

Any ideas where to start to look for issues?

 

[bushtech]

Could be blown led, but you'd need to open the TV to check the led's. Finicky job
See here:

 

[kellys_eye]

Plasma TVs don't use LEDs....

Disconnect output of power supply board and retest. If the PSU still won't start change the PSU module. You might have to fit a load to the PSU outputs to ensure regulation works properly though.

 

[bushtech]

Duh, sorry, stupid me

 

[phlox]

I unplugged everything except the two logic boards. The outputs of the psu are VA and VS and VSC . VS is supposed to be 207v , VA 58v and VSC -185v. However with backlight power boards disconnected i grt high readings but then quickly start dropping down , eventually to zero.

The 15v and 5v rails output fine.
I removed and checked the psu again. No damaged components or capacitors

 

[kellys_eye]

However with backlight power boards disconnected i grt high readings but then quickly start dropping down , eventually to zero.

Connect a resistor load to those outputs and retest. They may need some form of load in order to provide a REGULATED output. Are they DC outputs? Your measurements would do as you suggest if they were AC.......measured on a DC range.

No damaged components or capacitors

Faults don't always show as physical damage - semiconductors faults would be unnoticeable.

 

[phlox]

Ill have to check again if its ac or dc. What tipe or rating of resistor would work and how would i connect it?

Its not mission critical to get the psu working again..since i can just get a replacement psu but im just afraid if its not the psu and something else then its money wasted on a psu

 

[phlox]

I know there arent always visible damaged...but most semiconductors looks like diode packages and test fine though.. ill send pics

 

[phlox]

Hi all.. so aftet bit more troubleshooting , i found shorted IGBT and Diodes on the x-main board causing the power supply to go into protect mode.

The IGBT are RJ30H1 and diodes are SF5A400HD . Looks like they are obsolete components and i cant get then at our retailers. They are however on places like aliexpress. My question is do you guys know any good replacements? I did find a replacement IGBT but it has a higher collector emitter voltage. And higher amperage rating. Would those work?

And the same for the diodes.

Thanks