LG TV PSU MOSFETs keep exploding

[cmlewis89]

Hi folks,

So I need some help repairing an LG LCD 47LB5DF PSU. The main caps finally gave out after 17 years and I thought it would be a fun challenge to try to fix. I replaced the main 2 caps, both main MOSFETs (one (Q506) was shorted both gate ~ drain and drain ~ source, other (Q507) was fine), main 8A fuse, standby IC (U502), resistor to standby IC (R508), the 4 thermistors (one exploded - TH502), and a small cap (C510).

When the board is isolated, I'm getting stable voltages throughout. The main caps are charging at a stable 167V. I'm also getting a very stable 5.01V DC out of the standby voltage output pins (nothing out of anything else). Everything looks fine until I connect the PSU to the main board. Doing so causes one of the main MOSFETS to immediately explode followed by the main 8A fuse. It's always just the one MOSFET (Q506) that fails (shorts open gate ~ drain). The drain ~ short diode remains good.

I've tested basically all of the MOSFET drive circuit components and even replaced the drive IC (U600). I'm not sure where to look next for potential faults. I couldn't find a schematic, unfortunately, so I just uploaded some pics (I tidied up the solder joints btw). I'd appreciate any pointers in the right direction.

Thanks!

[Harry_22]

Hi!

It seems U502 is PFC controller and Q506 and Q507 are running in parallel.
Could you clarify U502 name.

[cmlewis89]

Hi,

U502 is an Infineon ICE3B1565J. The original had a shorted internal MOSFET from the power surge, so it was shorted closed CS ~ drain (pins 3 ~ 4). This is the datasheet I found on it: https://www.alldatasheet.com/html-pdf/152673/INFINEON/ICE3B1565J/1959/5/ICE3B1565J.html

That's correct, the 2 MOSFETs in question are running in parallel. The model # is: Infineon SD20N60.

[Harry_22]

Sorry PFC is another one U600, please see the picture.
Please send me the name as well.