BN44-00514A Repair

[FoxMulder]

Hey guys,

So I have a Samsung PS60E8000 that died. The bridge rectifier, main fuse and 1 of the power factor correction MOSFETs had shorted. I replaced all those and the set was working ok. Then again it failed. This time one of the FETs that powers Vs and Va had given up. I replaced both these FETs and the set still wont work. All the capacitors look ok.

Pulling the PSU out of the set, and applying mains power has the PSU click the relay on. This implies something is driving PS_ON low.

I get all the correct voltages STBY, D5.3V, 15V, but not Vs and Va. Wiring a 300 ohm resistor to link VS_ON and V_5.3 doesn't do anything.

I tried to work out what was driving PS_ON low on startup so I traced it out. Measuring PS_ON I was getting 1.6V. I traced this to the voltage divider formed by RQ890 (2.4k) and RQ825 (1k).



In order for PS_ON to be 1.6V it would mean that Pin 4 of UQ802 must be 0v. (5.3*1000/(1000+2400)) ~ 1.55V

I removed RQ890, RQ825 and CQ817 and I measured 3 Ohms to ground on Pin 4 of UQ802. I'm assuming UQ802 is stuffed, however it looks to be some sort of micro-controller and thus I would need the firmware to reprogram a new one.

Anyone have any luck replacing UQ802? Or any schematics for this board? I might be better off binning the TV as a new PSU is around $200.

Thanks,
Asela

[FoxMulder]

If anyone else is curious, I managed to find someone with a board and they posted it to me. Sure enough Pin 4 of UQ802 on the new board is at high impedance when off. New board is currently operating in the TV. UQ802 is a microcontroller with Samsung code on it, but no one else has the code. If it fails, Samsung will only sell the board (which is of course no longer produced) not the component. It would be possible to rig up a PIC or other micro to perform the same function if it ever fails again, however part of me thinks the effort required to do so, might as well just buy a new TV.

[Hornnumb2]

Did you look on shopjimmy for a repair kit.

[TheN00b]

A repair kit probably won't have this sort of thing in it. OP, have you desoldered it and checked the bottom of the chip? Sometimes important info can be silkscreened onto the bottom. If not, then you may want to scrape off the top plastic of the chip VERY CAREFULLY to see if there is any writing.