LG 50 PC1DA PSU blowing fet's

[Cornboats]

I'm trying to fault find down to component level on an LG 50PC1 JO12B power board.
The fuse blows on the board and also trips the house breaker on start up. I've removed 2 banks of fet's and changed 2 fets which had blown. Refitted and tested but now all fets in 1 bank have blown. I've tested some of the larger components around the fets on the board without finding any faults.
I've connected to 2x100W lamps in series to test the board out of circuit. On both occasions and the lamps come on and off with the relay operation exactly like a working psu. When the board has been connected to the tv 2 10amp circuit board fuses have blown so far. Should I leave these lamps in the circuit when connected to the tv to avoid blowing more fuses?
Any help or advice would be much appreciated.

[Ltank]

Re: LG 50 PC1DA PSU blowing fet's

The fact that the boards input fuse blows tells me the problem is in the primary side of P.S. Check the bridge rectifier or diode for shorts. Check the main 450 vdc filter cap for starters.

[Cornboats]

Re: LG 50 PC1DA PSU blowing fet's

Hi. I've pulled both bridge rectifiers and they didn't read a dead short but now you've mentioned them I'll pull again and measure against a known working one.
The 2 filter capacitors are 450wv 330uf & measured 08 ohm esr when I pulled them so I thought these were ok although I didn't compare them against known good ones.
I'll let you know the results of the bridge rectifiers.
Have you connected psu's through lamps to save blowing fuses? I thought it might be a good idea to save blowing fets and fuses. When the fuse blew it sounded like a rocket going off.
Thanks for taking the trouble to reply.

[Alastair E]

Re: LG 50 PC1DA PSU blowing fet's

These lamps you connected......

Where did you connect them? To the Vs supply Out of the PSU, or in series with the mains TO the PSU....?

IF you've got blowing MOSFETS --then there's a problem with the Drive circuits to them, ie--the Chips and drivers to the Gates of the MOSFETS....
--The ones you've pulled out of the PSU are for the PFC....

[Cornboats]

Re: LG 50 PC1DA PSU blowing fet's

Hi Alistair.
I connected 2 100watt 240v bulbs in series prior to mains input on the board but with the board on the bench for initial testing after I fitted new fet's.
The lamps responded as a normal working board ( fortunately I have 1). The lamps came on and off in unison with the relays. I didn't fit the lamps once I'd refitted the psu back into the tv but having had 2 blow ups I'm now wondering wether I should have done so as a precaution.
Could a damaged chip cause mutiple failure of 3 fets?
Thanks for the attachment which I'll peruse.
Thanks for taking the trouble to respond.