Samsung SyncMaster T19B300 Repair

[walterharriman]

I recently acquired a Samsung SyncMaster T19B300 18.5" TV monitor, completely dead - not even any life from the LEDs under the capacitive front panel buttons. Opened it up (yes, I understand about SMPSU voltages and dangers, though I have done little work on them - I have been discharging capacitors safely and using a Fluke meter) and followed the First Rule of Troubleshooting  - tada, apparently no output, except for one rail which was under voltage!  Removed the PSU and looked in more detail. First of all, recapped it - being a Samsung TV, I'd probably have to do it eventually anyway - and tested again. Still same as before! Next, tested more components in detail. Found a Schottky diode which was open both ways at position DM861 on the board and replaced that with an equivalent part (checked datasheets) - still the same! I can't find any other obvious potential points of failure (obviously fuses etc are good), and can't find anything on these symptoms - the person who gave the TV to me said it just randomly wouldn't turn on one day.

The bridge rectifier is giving out a steady 335V, whilst Vamp, B5V and B13V are all completely dead. A5V holds at around 3.68V, whilst Vled is at 0.95V. I have noticed the P_ON and B_ON pins in the power connector - this could be a PEBKAC on my part, but might it be necessary to short one of those pins to ground or A5V, ATX style, to bring the PSU up?

Thanks guys!

Images:

P.S. I haven't bothered cleaning the flux residue off the board because I'm still working on it. Also, my iron sucks.

[tautech]

How's this going?

[walterharriman]

I'm beginning to wonder if there might be an ID10T error here. I don't pretend to be an SMPSU expert, but there is no logic on the board that could communicate with the digital board to receive a power-on signal (the single IC on the bottom is a MAP3204 4-channel LED driver for the backlight). Maybe P_ON is "power on" and B_ON is "backlight on"? Do you think shorting one or the other to ground might bring the supply up - I see around 2.2-2.3V on P_ON with the meter.

[fluxcapacitor]

can you recheck your solderind to the left of capacitor c966 underneath .