Hi everyone
I have a LG plasma with the dreaded relay-clicking fault.
Model 42PG60UD (manufactured September 2008)
Power Supply Samsung EAY41360401
Mainboard 60PG30UD-AA
I received this as a non-working set, so I don't have any insight into its history, or the circumstances of its failure. I'm in Brisbane, Australia, and there's a good chance that it has operated in above-30C temperatures for some of its life (although there are no components showing any signs of heat stress).
When AC is connected, the red LED on the power switch lights momentarily, and a relay clicks inside. There follow 6 short flashes of the green LED on the power switch, then the red LED again for slightly longer, then the relay clicks, clicks again, and the sequence repeats two more times. The relay stops clicking, and the power switch just flashes short greens after that. The power switch does not respond to pressing, either during the relay clicking or afterwards. The set does not respond to the remote, which has fresh batteries, at any time.
During the relay-clicking sequence, the screen briefly lightens to a dark grey, the rest of the time it is black.
When I disconnect the mainboard from the ps at P803 (lower RH corner of ps board), the relay clicks once and the green LED on the control board comes on. Voltages measured at P801 are
Vs 185.6 Vdc
Va 60.0 Vdc
M5V 5.02 Vdc
Meanwhile at P803
5V_det is 5.0 Vdc
ac_det is 5.04 Vdc
All voltages are steady.
Bridging the Autogen pins on the control board starts what I assume is the standard check pattern sequence. The display and its drive appear to be working fine.
When I reconnect the mainboard at P803, I get the same symptoms as above exactly, every time. Voltages at P801 are now:
Vs varying between 100-300 mVdc (instead of 185V)
Vs alternates between 1.6Vdc and 60 Vdc (as the relay clicks)
M5V alternates between 0.7V and 5.0Vdc (as the relay clicks)
5V_det is 4.7 Vdc, dropping to somewhere below 1 Vdc when the relay clicks on and the green LED on the control board is lit
ac_det is a constant 4.5 Vdc, regardless of whether the relay is on or off.
PS fuses F101 and F801 test ok. Caps on ps look okay, no obvious bulging or leakage, but I haven't tested them electrically.
The fault is similar to that described in https://www.badcaps.net/forum/showth...light=42PG60UD, and I'm leaning towards the same conclusion: a bad mainboard. Before I take the plunge I'm wondering of anyone else has seen this (or similar) fault, and whether there is anything else I should check. I believe there may be some diagnostic output from the serial port, but I'm not sure how to access it, or what format it would be in.
Images of ps and mainboard attached
Thanks in advance
I have a LG plasma with the dreaded relay-clicking fault.
Model 42PG60UD (manufactured September 2008)
Power Supply Samsung EAY41360401
Mainboard 60PG30UD-AA
I received this as a non-working set, so I don't have any insight into its history, or the circumstances of its failure. I'm in Brisbane, Australia, and there's a good chance that it has operated in above-30C temperatures for some of its life (although there are no components showing any signs of heat stress).
When AC is connected, the red LED on the power switch lights momentarily, and a relay clicks inside. There follow 6 short flashes of the green LED on the power switch, then the red LED again for slightly longer, then the relay clicks, clicks again, and the sequence repeats two more times. The relay stops clicking, and the power switch just flashes short greens after that. The power switch does not respond to pressing, either during the relay clicking or afterwards. The set does not respond to the remote, which has fresh batteries, at any time.
During the relay-clicking sequence, the screen briefly lightens to a dark grey, the rest of the time it is black.
When I disconnect the mainboard from the ps at P803 (lower RH corner of ps board), the relay clicks once and the green LED on the control board comes on. Voltages measured at P801 are
Vs 185.6 Vdc
Va 60.0 Vdc
M5V 5.02 Vdc
Meanwhile at P803
5V_det is 5.0 Vdc
ac_det is 5.04 Vdc
All voltages are steady.
Bridging the Autogen pins on the control board starts what I assume is the standard check pattern sequence. The display and its drive appear to be working fine.
When I reconnect the mainboard at P803, I get the same symptoms as above exactly, every time. Voltages at P801 are now:
Vs varying between 100-300 mVdc (instead of 185V)
Vs alternates between 1.6Vdc and 60 Vdc (as the relay clicks)
M5V alternates between 0.7V and 5.0Vdc (as the relay clicks)
5V_det is 4.7 Vdc, dropping to somewhere below 1 Vdc when the relay clicks on and the green LED on the control board is lit
ac_det is a constant 4.5 Vdc, regardless of whether the relay is on or off.
PS fuses F101 and F801 test ok. Caps on ps look okay, no obvious bulging or leakage, but I haven't tested them electrically.
The fault is similar to that described in https://www.badcaps.net/forum/showth...light=42PG60UD, and I'm leaning towards the same conclusion: a bad mainboard. Before I take the plunge I'm wondering of anyone else has seen this (or similar) fault, and whether there is anything else I should check. I believe there may be some diagnostic output from the serial port, but I'm not sure how to access it, or what format it would be in.
Images of ps and mainboard attached
Thanks in advance
Attached Files
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