Samsung UN65KU6290F PS board blows fuses

[valvashon]

Samsung UN65KU6290F (May 2017); received from local Buy Nothing group. Was listed as "just went dead" and they wanted it gone. I brought it home, didn't notice anything visually wrong with the power supply board, looked up the cost of a new one and that's about as far as it went. Family was tired of tripping on the foot of the set so I decided to dig in and repair or toss.

Can't believe that I didn't check it earlier but I found the main 8 amp fuse blown. Jumped across it with a 10 amp blade style fuse and you can see that it literally exploded inside the second I plugged the TV in. Still nothing on the board looks burnt or melted. Nearly a dead short when measured (post fuse blow) across the + and - terminals of the bridge rectifier. Shouldn't be too hard to find what has shorted out but if anybody has any ideas I'd appreciate them. Pretty sure it's a power supply board problem given the explosive way the test fuse blew immediately upon power being supplied to the board.

Did a search on here finding some problems with the larger Samsung UN series of TV's but nothing like this.

[EazyBone]

Check qm801cs/802 and see if they read shorted. Known defect in other boards, try it out

[valvashon]

I was going to check all the TO220 devices today anyway but thanks for the heads up on the problem MOSFET devices. QP802CS is the shorted one, dead short across all legs. Others check OK but I will replace its companion QP801CS. Do we know if it's the brand of the MOSFET Samsung used (MagnaChip) or is the design of the board just hard on whatever MOSFET is in there? DigiKey carries Infineon Technologies MOSFETs and I will cross to one of those and just shotgun all 4 MOSFETs on that board if the MagnaChip ones are problematic.

Again, thanks for the help!

[EazyBone]

Not sure on answer, but yes replace both. Apparently a common failure. Then replace fuse and might be good to go. Make sure after replacing to check those blue caps around it also, if you have them might be good idea just to change them

[lotas]

If these mosfets burned out, then the PWM that controls them was probably also damaged and you need to look at all its wiring (smd low-resistance resistors, diodes, zener diodes...) they are located on the back side of the board. If you do not replace them, the new mosfets transistors will burn out instantly.

[valvashon]

The only other component that I have found that failed (besides the one MOSFET) was the common cathode dual rectifier just ahead of the MOSFETs in the circuit. One side/diode was shorted corresponding to the shorted MOSFET.

I have ordered the dual rectifier from eBay as I did not find a good cross at Digi-Key. That part number is SF10A600HPI by AUK. The Digi-Key cross was electrically compatible but in a larger case that would have required board and heat sink modification.

I did find an acceptable substitute for the MagnaChip MOSFET at Digi-Key. The part number is Infineon Technologies SPA11N60C3XKSA1.

Fuses are Littlefuse 0215008.MXESPP, 8 amp ceramic slow blow.

I have ordered extras of all of these in case it's more than the MOSFETs and the dual rectifier. I put down the part numbers in case it helps another Bad Caps member in the future.

Dual rectifier will be here at the end of December and I will post again with the results then.

[nomoresonys]

Simple to make dim bulb tester/current limiter, saves you from burning up components and fuses: https://www.youtube.com/watch?v=SKK6...W-EQh9LrN5i5YC

[PontyPCs]

QM801 and 802 are the PFC boost. Check the gate feed resistor and diode before replacing and powering on

[valvashon]

This TV is working again after a sum total of $7.86 worth of components, two FET's, a dual diode and a fuse. Of course I had to or did order extras and will be stashing some of those inside of the TV in case it happens again or some of the othiser FET's fail. The part numbers I used as replacements are listed above.

Thanks to everybody for their help on this. I am hoping that the information in this thread will help others in the future.

Val

[EazyBone]

Thx for reply.