LG 37LG10-UM won't stay on red green red

[axlmastr]

Hi,

I've posted in the computers section before but this is my first post in TV. I have knowledge with crappy cap syndrome spanning the past 12-14 years and have replaced thousands. I have some other board level experience reworking various electronics that fall prey to bad components or perils of nature.

37LG10-UM Symptom:

Apply power and the front panel displays a steady Red light
Press momentary power switch and the light changes to green for a split second and then back to steady Red.

I checked the power supply board for any obvious visual signs of failure but none were found. Taicons on the majority of the board with a few United Chemicon sprinkled in. I opted to listen to the board while pressing the power switch and heard a slight click sound coming from the Secondary side of the board. The single click has a duration lasting about as long as the described Red-Green-Red sequence. I locate the sound around the Secondary transformer. I decided to swap all of the caps with new pannies except for the largest one. No change. What next?

[budm]

Re: LG 37LG10-UM won't stay on red green red

I would find out first if the stby power supply is steady first, if it is this then start looking at the command signals from the main board feeding the power supply board to see what are present and what are not present.

[axlmastr]

Re: LG 37LG10-UM won't stay on red green red

I apologize for the delayed response, but This was not exactly a priority at the time since my friend owns this unit and just asked me to take a look since I've managed to repair plenty of friend's machines etc. My friend did go on eBay and purchase the exact same board for about $20 because he read that this was the likely culprit with this model of t.v. The used board from eBay has the same symptom leaving him frustrated and here we are.

I took some readings from the power switch to the logic board and on to the power supply board. I did read on the the connector (CN402) leading to the inverter board, never went into the inverter board.

The voltage on all hot pins from power switch/multi-function switch board, standby/power light board, and where it connects to the logic board are 3.2V at rest.

Connector from logic board to power board (CN401) is 16 pins and has from pin1 the following with reading when PWR SW pressed to the right:
LCD-BR 0
LCD ON 0
PWR ON 1.5-2.6V
5V 4.9V
5V 4.9V
5V 4.9V
GND 0
GND 0
12V 9.5-10.5V
12V 9.5-10.5V
GND 0
GND 0
14.7 13.6-13.8V
14.7 13.6-13.8V
GND 0
GND 0

Connector from power board to inverter (CN402) has 14 pins and readind the following in the same circumstance:

LCD BR 0
NC 0
LCD ON 0
NC 0
GND 0
GND 0
GND 0
GND 0
GND 0
24V 23.3-23.4V
24V 23.3-23.4V
24V 23.3-23.4V
24V 23.3-23.4V
24V 23.3-23.4V

As mentioned before when the PWR SW is pressed the transformer (T401) marked "1J.20244.011" makes two quick clicks during which the standby light changes to green and then back to red with no sign of the panel lighting up.

This transformer has approx 66V of input but no output to any of the secondary pins.

I can read primary side the circuit from input voltage of the board (120V) steps to 65.4-66V. Then tracing it through each transistor (D3SR60, K3562's & a XA1088) I find where it reads either 65-66V or 60-62V and also some that read 48-49V.

On the secondary side I see two transistor I can't read the part number on since they are under a soldered heatsink that read 13.8-14.4V on one and 10.1V on the other. Two other EN220A's read 23.8-24.2V each.

All of the electrolytics (mostly Taicon & United Chemi) on the power board were replaced with FC/FM Panasonics as I have always used at the time of my original post.

I recently swapped all of the Elite and Lelon electrolytics on the logic board with Pannies as well. These caps were in line with the circuit paths for the power/multi-function inbound connector (J5008) to the outbound connector (J5001) that cables to the power supply board connector (CN401). I looked at this circuit on the logic board as the "trigger" circuit to tell the power board to turn on the inverter and display circuits.

I'm not sure if any of this helps, but I hope so. I think the power board went and the one my friend purchased online was a dud too though he said they listed it as tested, working. I know that isn't always the case.

[budm]

Re: LG 37LG10-UM won't stay on red green red

"lcd-br 0
lcd on 0"

Main board is not sending the Backlight dimming control (LCD-BR), or the backlights on control (LCD ON).

[axlmastr]

Re: LG 37LG10-UM won't stay on red green red

Any suggestions on what to look for? Is it maybe a switching IC on the main board? I posted some pics.

I can trace thoss two circuits to the bottom side of the board and follow where they lead/ There some NAND type IC's on along the way (8 legged variety) I have experienced changing these with my hot air station on laptop motherboards for charging circuit issues. Nothing appears to be burnt. This symptom just "happened" one day with no indication of impending failure. TV just wouldn't turn on anymore.

[axlmastr]

Re: LG 37LG10-UM won't stay on red green red

Left connector in center pic is from the power pcb by way of the standby light pcb. It has the 3.2V in it. The connector to the right is CN401 that jumps over to the power supply board and carries the signal on for "lcd-br 0 & lcd on 0. The third pic is of the back side flipping the board right to left.

[budm]

Re: LG 37LG10-UM won't stay on red green red

May be checking Voltage regulator ICs, look for service manual, troubleshooting main board at component level without diagram will be really hard.

[axlmastr]

Re: LG 37LG10-UM won't stay on red green red

I wanted to update this thread with my findings. The power board turned out to be good even though they are known for bad caps. I did recap the board anyway. It turned out budm was right about checking for signals from the main board to the power board. The standby signal from the power switch to the main board was good.

When the power switch is pressed the signal goes to the main board and then is sent on as a 24V trigger to the LCD_ON and Backlight circuits to tell the power board to give power to the LCD, and Backlight by way of the inverter board. I found a good tested main board and installed it. The TV came on and showed a picture after all.

[budm]

Re: LG 37LG10-UM won't stay on red green red

Thanks for the follow-up on the repair.