Emerson LC391EM3 stuck in standby

[ZnsaneRyder]

Re: Emerson LC391EM3 stuck in standby

I want to add to this thread, since this incomplete thread has been helpful in the process of repairing an Emerson LC391EM3.

I downloaded the service manual, which helped me realize an issue with these televisions.

If the TV does not come out of standby, or turns on, then turns off, is because the mainboard is sensing incorrect voltage. (if the mainboard is good)

The original mainboard in the TV I am repairing FAILED, (no attempt to power on, no standby LED) and with the NEW main board I get a red standby LED. The 3.3V rail was producing over 5V (in standby) because Q701 (for the 3.3V regulator) failed short, sending the full 12V to the original mainboard, frying the mainboard. Once I replaced Q701 the proper 3.3V was present, and now the TV turns on. I have to reassemble the TV.

So YES, that is TWO FRIED BOARDS, but the PSU was repairable. Luckily the lowered 6.8V (standby for 12V rail) prevented cooking the new board.

Don't be so quick to disassemble the TV to get to the backlights/inverter, it is too much risk of damaging the LCD and CCFL bulbs.

Check the PSU if/when you get a standby LED.

[ZnsaneRyder]

Re: Emerson LC391EM3 stuck in standby

Updating post. The Television is working great. The larger transistor I used for Q701 produces less heat so the television should last a lot longer.

So with this Emerson, and the Magnavox equivalents, if you find the mainboard to be dead (no standby light) then the power supply is what blew the mainboard.

Beware of the 5V and 3.3V rails that use small transistors.