LG 50PQ30C-UA Troubleshooting steps:
Screen was not powering up.
Upon turning on the red LED goes to BLUE and stays there, meaning the system was on (sending out voltage). The display would however be blank (no light at all).
With Power supplied:
Checked all voltages on PS board (input and output). The following voltages were in line
Vs = 193V
Va = 60V
and all +5V terminals read as they should.
Voltages read correct at the connection points on X and Y Sustain boards also.
Looked at Caps and all caps on all boards looks good (not bulging or leaks)
With power off:
Checked fuses. All fuses on PS board were good. Fuses on X sustain were good.
Main fuse (4A 250V) on Y sustain board was acting irregular. It tested open after the TV has been powered off for a while.
However, it was testing good when power was applied, or right after TV was powered off. Fuses either work or don't so this made me scratch my head. I removed the fuse from the board and checked it...It was indeed opened.
Replaced the fuse on the Y-SUS board and reinstalled. When I try to power up the TV, the blue LED comes on momentarily, but the TV powers back down after a few seconds. The newly installed fuse remains intact. This indicated that the Y-SUS has a problem and rather than performing component level diagnostics, the board was replaced.
RESOLUTION 1:
Replaced Y-SUS Board as I figured it to be the culprit, bought refurbished from the site tvpartsguy.com
Symptoms got better but still no pic. The TV now goes through the power sequence with the new Y-SUS board.
Further check of the -Vy and Vsc voltages yielded that these voltages were not present on the board. They would jump around, but never get above ~6 volts. I tried different connection configuration to determine the cause.
I found that with the ribbon cable connected between the Y-SUS and Control boards this is when the voltages for Vy and Vsc went away. Upon disconnecting the ribbon cable and performing the checks with the TV on, the -Vy read 133.3V (with POT maxed out), for my unit this should read 135V. Vsc read 185 V as specified.
Performed all steps related to the control board and the board is working fine per the results. Also performed continuity check on the 30 pin ribbon cable and cable tested fine.
Here are some additional checks performed;
Diagnostics of the Y-Driver (buffer) boards per the procedure and yielded the following results;
(See attached word file with results)
Read open on two points that should have read 1.94V.
Reading were ok other than pins 11 and 12 read a bit low as shown.
There were quite a few points that read irregular as shown.
Also performed check for Auto Gen Test Pattern and got nothing. The PDP never comes on so there is no way to check any other image parameters.
I am now thinking buffer boards based on the test results, but want to be sure before spending more money, as I still have a gut feeling that the main board (with all the inputs) could be the culprit.
I am suspecting this because with power on and volume up, I get that “frying” sound like the one heard when on an unturned channel. However, and I change the input, regardless of where I stop, I get the same sound. Though there is no picture and I can't see what input I am on, I would think if I stop on a digital input (HDMI, DVI), the sound would stop…right? As these inputs normally do not have that frying sound associated with them. The other thing I am not sure of is the Vy and Vsc voltages on the Y-SUS board. I am stumped and could use some help. I am doing this as a challenge, and yes I am being challenged.
Screen was not powering up.
Upon turning on the red LED goes to BLUE and stays there, meaning the system was on (sending out voltage). The display would however be blank (no light at all).
With Power supplied:
Checked all voltages on PS board (input and output). The following voltages were in line
Vs = 193V
Va = 60V
and all +5V terminals read as they should.
Voltages read correct at the connection points on X and Y Sustain boards also.
Looked at Caps and all caps on all boards looks good (not bulging or leaks)
With power off:
Checked fuses. All fuses on PS board were good. Fuses on X sustain were good.
Main fuse (4A 250V) on Y sustain board was acting irregular. It tested open after the TV has been powered off for a while.
However, it was testing good when power was applied, or right after TV was powered off. Fuses either work or don't so this made me scratch my head. I removed the fuse from the board and checked it...It was indeed opened.
Replaced the fuse on the Y-SUS board and reinstalled. When I try to power up the TV, the blue LED comes on momentarily, but the TV powers back down after a few seconds. The newly installed fuse remains intact. This indicated that the Y-SUS has a problem and rather than performing component level diagnostics, the board was replaced.
RESOLUTION 1:
Replaced Y-SUS Board as I figured it to be the culprit, bought refurbished from the site tvpartsguy.com
Symptoms got better but still no pic. The TV now goes through the power sequence with the new Y-SUS board.
Further check of the -Vy and Vsc voltages yielded that these voltages were not present on the board. They would jump around, but never get above ~6 volts. I tried different connection configuration to determine the cause.
I found that with the ribbon cable connected between the Y-SUS and Control boards this is when the voltages for Vy and Vsc went away. Upon disconnecting the ribbon cable and performing the checks with the TV on, the -Vy read 133.3V (with POT maxed out), for my unit this should read 135V. Vsc read 185 V as specified.
Performed all steps related to the control board and the board is working fine per the results. Also performed continuity check on the 30 pin ribbon cable and cable tested fine.
Here are some additional checks performed;
Diagnostics of the Y-Driver (buffer) boards per the procedure and yielded the following results;
(See attached word file with results)
Read open on two points that should have read 1.94V.
Reading were ok other than pins 11 and 12 read a bit low as shown.
There were quite a few points that read irregular as shown.
Also performed check for Auto Gen Test Pattern and got nothing. The PDP never comes on so there is no way to check any other image parameters.
I am now thinking buffer boards based on the test results, but want to be sure before spending more money, as I still have a gut feeling that the main board (with all the inputs) could be the culprit.
I am suspecting this because with power on and volume up, I get that “frying” sound like the one heard when on an unturned channel. However, and I change the input, regardless of where I stop, I get the same sound. Though there is no picture and I can't see what input I am on, I would think if I stop on a digital input (HDMI, DVI), the sound would stop…right? As these inputs normally do not have that frying sound associated with them. The other thing I am not sure of is the Vy and Vsc voltages on the Y-SUS board. I am stumped and could use some help. I am doing this as a challenge, and yes I am being challenged.
Comment