Samsung LN46D550 Won’t Turn On

Other model numbers include LN46D550K1F and LN46D550K1FXZC

This TV went through the motions of turning on but didn’t.  The front led flashes and then goes out with no picture and no backlight.  BLU_ON and PS_ON signals were being sent from the main board.  I put alligator clips across the large caps to check the PFC voltage and it peaked at 430VDC when the TV  is first plugged in before dropping to an off-state of 165VDC.  I suspected an overvoltage condition was occurring causing a shutdown.

I couldn’t find a schematic for the power supply board BN44-00441A.  The closest I could find was for BN44-00341B.  Shopjimmy has a repair kit for the board which included ICP801 which is the PFC controller.  I couldn’t read the markings for this part and figured it out it must be a FAN7930B since pin 2 was being used as an OVP detection line.  The part is available at Digikey part# FAN7930BMX-GCT-ND

It was a little difficult to remove the part probably because it may have been glued underneath.  After replacement, the TV turned on and the PFC voltage was stable at around 395VDC.

Because the power supply had crappy Samwa capacitors, I proactively replaced these as well.

CM809, CM811  – 680uF/25V
CM818 – 2200uF/10V
CM825 – 470uF/10V


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