Lg 32le4900 no video,sound and backlights

[omega14]

The tv turns on but the screen is black and no audio.When the mainboard cable is connected to power supply at a certain angle(ie '/') , the backlights will turn on but still no video and sound. I also checked blue connector pins powering the driver board when connected. I found out the drv_on pin voltage is missing , but found on error pin. Is it the mainboard is not sending signal to power supply turn on backlights? If so how do I rectify it?

[dick_barton]

Re: Lg 32le4900 no video,sound and backlights

Can you post sharp focused pictures of your boards top and bottom. You may well have poor solder joints but since we cannot see the set then good pictures are the next best.

[omega14]

Re: Lg 32le4900 no video,sound and backlights

Can you post sharp focused pictures of your boards top and bottom. You may well have poor solder joints but since we cannot see the set then good pictures are the next best.

DSC_139 PS with mainboard cable connected to ps black connector as normal. No backlights.
DSC_142 PS with mainboard cable connected to ps black connector at an angle. Backlights only
DSC_141 PS other side of the board where components are soldered.
DSC_143 mainboard side A.
DSC_145 mainboard side B.

[dick_barton]

Re: Lg 32le4900 no video,sound and backlights

Some of the solder joints on the bottom of board are not very good and I think may not be connected. I would solder the joints again and make them good. It seems that a lot of components have been lifted.

[omega14]

Re: Lg 32le4900 no video,sound and backlights

Some of the solder joints on the bottom of board are not very good and I think may not be connected. I would solder the joints again and make them good. It seems that a lot of components have been lifted.

Thanks for your reply. I am going to try out what you've asked me to do.

[jonny78]

Re: Lg 32le4900 no video,sound and backlights

sorry to post on a old thread but i have the exact same tv with EXACTLY the same problem! tv turned on but no backlight or picture i then put the cable running from the mainboard to the psu at an angle and managed to get the backlights working but no picture! i tried what dick suggested and resoldered as many points on the psu as i could but thats hasnt sorted the problem..wondering if this is a mainboard problem as ive seen a repair service for this particular model on ebay think it was the eeprom!

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

Hello, I don't suppose anyone was able to figure out what the problem was here? Another 32LE4900 with exactly the same symptoms. Thanks in advance if anyone knows how to fix it!

[budm]

Re: Lg 32le4900 no video,sound and backlights

Hello, I don't suppose anyone was able to figure out what the problem was here? Another 32LE4900 with exactly the same symptoms. Thanks in advance if anyone knows how to fix it!

Since original OP never provide the Voltage reading on the connector of the power supply that goes to the main board when TV is OFF and when power switch is activated, we will need that info.
You also need to provide good clear straight shots of the whole top and bottom side of YOUR board.

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

Okay, I have taken voltage readings on the power board at the pin connector. What do you think? The invertor board and main board have already been swapped out with second hand replacements from ebay without success.

Again, with the wiring loom connected at an angle, the backlights come on and also light up individually when powered from my LED tester. I also noticed that there was no voltage in at a test point on the T-Con board.

[budm]

Re: Lg 32le4900 no video,sound and backlights

DRV_ON (BL-ON) control signal from Main board is not present.
Do you get 12VDC at both ends of the SMD fuse on the T-CON board with ref. to the chassis ground when TV is turned on?
ERROR pin shows 3V when TV is on, not sure if that is normal or bad, need to do research on that.

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

Have just checked and I get 0V on the T-Con board. I understand the SMD fuse you refer to is marked P on green in the photo below, and that is where I tested.

[budm]

Re: Lg 32le4900 no video,sound and backlights

Have just checked and I get 0V on the T-Con board. I understand the SMD fuse you refer to is marked P on green in the photo below, and that is where I tested.

Yes, that is the fuse F001.
The switched 12V for running the T-CON board is from the main board, the 12V from the power supply board is fed to switch to supply switched 12V to the T-CON when TV is turned on, so the reason you do not have DRV-ON (BL-ON) is that there is no 12V for T-CON so main board stops sending the BL-ON signal, some TV is setup like that. So you need to locate the P-CH MOSFET that is used for switched 12V to see if the Source pin is fed with 12V or not and the Gate pin is at least 3V < Source pin or not for the MOSFET to be on.
Also we do not know for sure if the replacement board is good or not for sure.

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

Thanks, I don't suppose you'd be able to assist with identifying the P-CH MOSFET? I believe the attached service manual covers this TV as well. It'd be useful to confirm if the problem lies with the main board.

[dick_barton]

Re: Lg 32le4900 no video,sound and backlights

I think Q409 is the panel power control mosfet. Page 20 of pdf.

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

Thanks for the heads up. I wasn't able to reconcile the components on the main board with those in the service manual that I originally provided. However, it'd seem that this LD03D chassis version does, and I can report that I get 11.7V on Q8004 at both the source and gate?

[dick_barton]

Re: Lg 32le4900 no video,sound and backlights

The gate should be abou 1.8V if transistor Q8003 is being switched on. Check the voltage on the collector (C) of Q8001 in standby and out of standby.

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

Okay, so I get 0V at C on Q8001 both in and out of standby.

[dick_barton]

Re: Lg 32le4900 no video,sound and backlights

With the set powered off, can you measure with your meter set to ohms, the resistance between collector and emitter of Q8001.

[mattd_robinson]

Re: Lg 32le4900 no video,sound and backlights

If I am reading this correctly, I see .923 with the dial set to 2K.

[budm]

Re: Lg 32le4900 no video,sound and backlights

If I am reading this correctly, I see .923 with the dial set to 2K.

923 Ohms In both directions if you swap the meter leads?
And Q8003 Base also shows 0V, correct?