This 37" LG LCD was my parents' but when it died early in the year they decided to buy a new one. I intended to work on it eventually and was recently forced to look at it after my Panasonic plasma started playing up.
The LCD would not turn on. Apparently they had been watching it when it made a loud bang and died. Upon further inspection I found that the 2.2R resistor supplying the mains DC bus voltage to the Standby 5V regulator had burned out. I couldn't find a short on the MOSFET of the switching regulator so figured I'd just try replacing the resistor. I did so and strangely enough it worked! I plugged the board back in and the TV was working. Except for one issue: a loud power supply squeal.
Even when the set was in standby the squeal was audible, but when powered on the squeal was far too loud so the TV definitely isn't usable like that.
I read that squealing can be caused by faulty other boards in the TV so I pulled the power supply and set it up on my workbench. I strung a 47R 5W resistor across the STBY5V output so that it was drawing 100mA and the squealing noise was being made. So it's definitely a problem with the power supply board.
I thought perhaps the 2200uF 10V filter cap on the STBY5V was failing but replacing it made no improvement.
I've got the service manual for the 37LC7D but the LG service manuals seem really poor in comparison to Panasonic ones. It does not include schematics for the power supply board, which is an EAX32268301/9.
The Standby 5V regulator IC is an ICE3B1565J and the PSU design is pretty similar to that presented in the datasheet.
It's really strange that the 2.2R resistor just died like that without any other issues. There's no charring on the board so it wasn't a failure due to gradual overheating (as would be caused by, say, mildly excessive current draw).
Do you component level repair gurus have any suggestions?
The LCD would not turn on. Apparently they had been watching it when it made a loud bang and died. Upon further inspection I found that the 2.2R resistor supplying the mains DC bus voltage to the Standby 5V regulator had burned out. I couldn't find a short on the MOSFET of the switching regulator so figured I'd just try replacing the resistor. I did so and strangely enough it worked! I plugged the board back in and the TV was working. Except for one issue: a loud power supply squeal.
Even when the set was in standby the squeal was audible, but when powered on the squeal was far too loud so the TV definitely isn't usable like that.
I read that squealing can be caused by faulty other boards in the TV so I pulled the power supply and set it up on my workbench. I strung a 47R 5W resistor across the STBY5V output so that it was drawing 100mA and the squealing noise was being made. So it's definitely a problem with the power supply board.
I thought perhaps the 2200uF 10V filter cap on the STBY5V was failing but replacing it made no improvement.
I've got the service manual for the 37LC7D but the LG service manuals seem really poor in comparison to Panasonic ones. It does not include schematics for the power supply board, which is an EAX32268301/9.
The Standby 5V regulator IC is an ICE3B1565J and the PSU design is pretty similar to that presented in the datasheet.
It's really strange that the 2.2R resistor just died like that without any other issues. There's no charring on the board so it wasn't a failure due to gradual overheating (as would be caused by, say, mildly excessive current draw).
Do you component level repair gurus have any suggestions?
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