DYNEX HV AC POWER SUPPLY 2nd FAIL

[circuit_breaker]

I have replaced 3 paralleled 40V dual P+N channel MOSFETS on the HV power supply board. The board is set up with two fuses on the 24 Vdc input feed. I found one fuse blown and replaced it only to find the 3 MOSFETs damaged (via ohm meter test). The power supply worked well for about 2 weeks and now the problem has repeated. It appears the same 3 MOSFETs are blown again.

The PCB had a few traces that were lifted during the repair process but I was able to add some wire wrap jumpers to get the circuit functional the first time.

The original problem which has returned is solid audio but no backlights. Please advise thanks! I have a picture of the board and will post when I learn how.

[circuit_breaker]

Re: DYNEX DX-40L260A12 TV BACKLIGHTS

The HV inverter power supply (INV40N14B) blew one of the two fuses on 24 Vdc input. The fuse and replaced dual P+N channel MOSFETs are circled in RED on pic. However after replacement the set only worked for about 3 weeks and now the "no backlight" problem has returned. It appears the same 3 MOSFETs are shot. This TV set has only 14 CCFLs and the blown section appears to be underdesigned. The two rightmost transformers drive 4 tubes each with 4 FETS in parallel. The leftmost transformer (smaller than other 3 XFMRs) drives 2 tubes with 3 FETS in parallel. The section that blows the FETS drives 3 tubes with 3 FETS in parallel.

I am wondering if a AC line transient could be causing the problem or if the HV could be arcing, etc due to an assy. issue. We are at 7000 ft altitude here which helps an arcing issue to occur.

I miss the SAMS photofact!

[circuit_breaker]

Re: DYNEX HV AC POWER SUPPLY 2nd FAIL

here are PICs

[ReeceyBurger123]

Re: DYNEX HV AC POWER SUPPLY 2nd FAIL

Ahh classic example of Samsung crap egineering! I fixed one exactly like yours you need to make sure to check the following:

Replace control Ic SEM2107 this drives the fets and can cause them to blow as in my experience it messes up the VCC voltage which blows the fets instantly.

Resolder all Smd parts, by this I mean almost every little device on the Pcb broken solder joints cause intermitent issues that causes them fets to blow.

Check for any other cold solder joints.