TV does not start - backlight blinks 3 times, red standby LED turns on
I have a UN55MU7600FXZC (Rev FC04) that died (assuming after a power surge) -> no red standby light
I tried all standard basic diagnosing (change plug, change outlet, change cable, change everything)
I opened the TV found the following:
Power supply Board:
- model: BN44-00876D
- type: BN94-12395C
- model: BN41-02568
- code: BN97-12813A
I tried disconnecting the main board from the power supply and I can observe all backlights coming on though the holes in the back
I took out the power button and tested for connectivity.
I replaced the following parts:
- Power supply with identical model (though it was the power supply)
- Checked all voltages on the connector that goes to the mainboard and are all in line with what is expected based on other articles here
- Checked voltages going to the backlight and they are in line with what is on the board (and the backlight turns on so that should be ok)
- Main Board with a SIMILAR model (BN94-11914C) which according to the Samsung parts website, is compatible with my model (Samsung BN94-11914C Main Pcb Assembly). In fact the label on the new main board lists my tv model: UN55MU7600FXZC
After replacing the main board I am getting different symptoms:
When plugged in, the backlights turn on or a second, they go off for a second, they turn back on at half brightness for a second, they turn off, and after another second the red standby light comes on. When the red standby light comes on, you can hear a buzz from the power supply (as if it tries to power on) and then the buzz goes away, the standby light goes off. Wait 5 seconds, the cycle starts again.
Things I tried (with both power boards)
- Press the power button - no change, cycle continues uninterrupted
- Press the power on the remote control - no change. (Although you can see the IR sensor on the tv blinking rapidly when the remote control button is pressed.
- Disconnected the speakers from mainboard - no change
- Disconnected the wifi module from main board - no change
- Disconnected the mainboard from power supply - backlights come on, solid, stay on.
- Disconnected the backlight connector from power supply - nothing turns on.
Someone on the internet suggested this could be a faulty screen... but I find it hard to believe. could it be that the main board is a different code than my TV that is causing this? Even if the Samsung website recommends them as compatible?
Note: I temporarily disconnected the speakers and the WiFi module since they seemed to have no impact connected vs disconnected
Video with behavior when plugged in: