Samsung LN40B500P3F Backlights Flash

Model LN40B500 LN40B500P3F LN40B500P3FXZA

When turned on, the backlight would come on for a second, turn off and this would repeat for a couple of times. Power supply part number is BN44-00264A. Schematic is available online. This badcaps thread indicates potentially bad transfomers on the inverter or bad ccfl bulbs in the backlight. I hooked probes to the main filter cap to monitor the PFC voltage and it was steady around 390VDC throughout. The thread indicates to connect a wire to pin 10 of the UI801 to see if the overvoltage protection was being triggered from faulty bulbs. This signal was high when the backlights were on confirming the fault. The thread also mention to bypass CI805 on pin 2 which should keep the backlight from shutting off. This modification worked as well. I put a plain white image on the screen and could verify a few bulbs were dim and triggering a fault.

Since the LCD TVs are becoming old and obsolete, I decided to scrap the TV and was able to use the main board on a LN46B500 TV I had.

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