Samsung plasma power supply repair

[dans2530]

Hi everyone,
This is my first post and topic! 

I have a very weird problem with a samsung power supply, bn44-00222a, it works fine until you turn up the plasma cell brightness then it shuts the tv down. The vs voltage sags lower until, I'm assuming, some protection circuit cuts the power to the board.

I have measured across the main caps and they read about 350v, far too low. I did some additional tests and found that the power factor controller (L4981A) wasn't producing an output to drive the mosfets. I replaced the IC, same deal. It is getting power as this was the first thing I checked (15v).

I took out the L4981A sub board and powered it up from a bench power supply, and it produces a 90% duty cycle from its output. So it seems to work.

If anyone has a schematic for this power supply it would help me immensely, I can't seem to find one, or if anyone can offer their opinion on where I should look that would help too as I'm out of ideas.

I have been reading this forum for a while, so I know there is a lot of sharp people on here that will have a good idea how to fix this. 
I will upload pics as soon as my phone is charged, they are all on there.

Best regards to everyone,
Dan.

[nukie]

Check the blue monolith caps for short. I have seen it twice now on Samsung plasma. If you have a thermal cam you will see it glowing nicely. I swap it with  ceramic on both clients screens still working after two years.