Thanks again 'MON2'

In answer to your questions -
-Confirmed - Only LED0301 is lit (It dips for 1/3 sec, slightly after the power button is pressed). All other LEDS are off.
-ALL_SYS_PWRGD is at 0v, Oscilloscope confirms no bursts of signal.
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These are the Boardview and Schematic files I'm using
" Apple iMac 27 A1419 J17 PVT 820-3478-A – Boardview (.brd).brd "
and " ***********_J17_MLB_051-9884_820-3478.pdf "
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Thanks 'mon2', info much appreciated.

-Found - Logic Board Part No 820-3478-A See pic below. Located on bottom edge of board, hidden by case when installed. Easy to find when board removed & you know it's copper etched under black soldermask.

-High voltage warning acknowledged. (Have been working with same for 50ish years, had a few zaps but still here)

-Have metered out (to ground) every inductor big and smallish. No shorts obvious. Inductors near CPU around 20 ohms (as expected?). (I have also checked vast majority of caps for shorts)

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Update: PP5V_S5 was not shorted to ground, probe was probably touching conductive screen ribbon when I was probing deeply under edge of case.

The Logic board has a "CE3E 31PITMB00H0" sticker if that is of any help.​

I have worked thru the boardview netlst, testing all obvious PPxxVx_xx lines (PP12VACDC, PP12V_G3H, PP12V_LCD, PP12V_S0, PP12V_S5, PP1V05_50, PP1V2_S4_camera, PP1V5_S0, PP1V8_S4_camera, PP3V3_G3, PP3V3_S0, PP3V3_S3_VRefmrgn, PP3V3_S5, PP3V3_TBTLC, PP3V42_G3H, PP3V42_G3H_SMC_SPVSR, PP4V5_Audio_Analog, PP5V_S0, PP5VS0_GPU_VCore_VCC, PP5V_S0_HDD,...

Hi, EMC 2639 .iMac not starting up. Single dim diagnostic LED (LE0301) flashes off briefly when power button pressed. Working through supply rails at present (PP5V_S5 appears shorted to ground but still early days)

Using Boardview 820-4652 but not sure if that is correct one to use. Have searched Forum but only found bios found for 2639 so far.
Have also tried 820-00134-08 and 820-3478 but have noticed discrepancies compared to my board.

If anyone has correct BOARDVIEW and SCHEMATIC for a EMC 2639 I would really appreciate it before I get too far into this.
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Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.



I looked at the CK1 through CK8 signals on both display boards with an oscilloscope.
All the signals on the unmasked side looked similar having a nice square 32.8vpp 17.1Khz squarewave chopped up by 50Hz 'sync or blanking' pulses. base of pulses at -6.8v, peaks at +26v.
There is a ~45degree phase change on each of the CK signals ‘sync' pulses to give a 360 degree spread as you go from CK1 to 8.

On the side I had masked off the CK1 thru 8 signals there was a messy...

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

My First BadCaps Post
I have a Samsung UA50TU8000W. It has a single ribbon cable going to the display boards.
I have achieved a reasonable fix after reading through this and several other posts and Youtube videos. Thanks Folks.

CAUTION I noted that the Mains capacitor on the power board does not appear to have a discharge resistor and was still over 250v half an hour after disconnection.

Symptoms-
1- When power connected Screen remains black. Back-light initially...