LG 55LW9500 no video, no audio

[krustyone]

Hi all,

I have an LG 55LW9500 that powers on by remote and the sensor touch and yet displays no image or back light.

There is no image with a torch.

24v is available to both LED driver boards and all supply rails check out ok going to the mainboard.

I tried hot air reflow of the CPU on the mainboard with no change.

Before I spend money on a new mainboard, does anyone have repair pointers for an EBT61548601 mainboard.

Thank you.

[dick_barton]

Re: LG 55LW9500 no video, no audio

Do you have any photo's of the circuit boards. Have you taken any other voltage measurement? Would be helpfull to diagnose the set.

[krustyone]

Re: LG 55LW9500 no video, no audio

Here you go.

Checking voltages now.

[krustyone]

Re: LG 55LW9500 no video, no audio

Ok. All voltages to and on the mainboard checkout ok and are within tolerances.
All on board power rails are correct.

All voltages on the TCON board appear to be missing.

PDIM is at 3.2v
INV_ON = .038

The heatsink above the XD Engine is warm to the touch.
TCON processor is cold.

There are 2 flashing leds on the LED driver boards that are flashing in sync.

Anywhere else you would like me to check?

[budm]

Re: LG 55LW9500 no video, no audio

"INV_ON = .038"
So you do not have control Voltage from main board to turn on backlighst circuit (<1V = OFF, > 2.5V = ON).

"All voltages on the TCON board appear to be missing"
So are you getting 12VDC at both ends of the SMD fuse, ref. to chassis GND. on the T-CON board?

[krustyone]

Re: LG 55LW9500 no video, no audio

Thanks for your help budm.

I couldn't find the SMD fuse you spoke of however, I traced back what should be the 12v rail at the TCON, which is reading +0.96v back to the mainboard.

The source of Q507 in the PANEL_POWER section is reading 12v as it should coming from L511, PANEL_CTL is reading high at 3.5v however the drain of Q507 is reading +0.96v, the same as the TCON.

I suspect Q507 has failed.
Apparently it is common to replace Q505, Q506 and Q507.

Can someone please confirm my theory.

Thank you.

[budm]

Re: LG 55LW9500 no video, no audio

The Panel_CTL is active LO, so for the Q507 to be ON, the Panel_CTL has to go LO.
Q507 is P-CH so for Q507 to be turned on, the Gate has to be at least 3V less than Source pin, so check that, also check the output again by disconnecting the LVDS cable to the T-CON.

BTW, this is about the same circuit used in this thread which has shorted Diode on the T-CON board.
https://www.badcaps.net/forum/showth...124#post956124

[krustyone]

Re: LG 55LW9500 no video, no audio

I checked the gate and source pins and they are both at +12v.

After disconnecting the LVDS cable, the +0.96v is no longer present.

The next step is to trace back the PANEL_CTL signal to IC602 which appears to control the main on/off functionality and miscellaneous related tasks.

Suspect the chip is working with some level of normality as the IR function is working however, I'm not sure what the purpose of the MICOM MODEL OPTION to the bottom left of the image.

[Nick's Tvs]

Re: LG 55LW9500 no video, no audio

We fix one of these guys almost every single day at our shop. 90% of the time, the issue is due to the Main processor chip having cracked solder joints on the Main board.
The main board is your green circuit board with the HDMI ports on it, I have a link below with a picture of the board:

https://www.nickstvs.com/store/p2564/EBT61579914.html


That module if you take a look at it has a large black heatsink in the middle. Remove power to the TV, and take a hot air gun, and warm up that heatsink for about 45 seconds. If you don't have a hot air gun, you can try using a hair dryer.
After the 45 seconds, go ahead and plug the TV back in and boot it up. If the TV turns on with good picture and backlight, then you have confirmed the issue is due to cracked joints on that main processor board. Now this is only going to allow you to turn on the TV once before it cools down, then it will stop working again and you will be back to square one, this is by no means a repair of any sorts, just a diagnostic trick to confirm the source of the failure.
If this is indeed the failure, you will need to either, reflow, reball, or replace the chip.

If that doesn't take care of it, the other 10% of the time we see the failure is on the silicon image chip aka your HDMI chip located next to the HDMI ports. In order to verify if it is in good condition or if it has failed, check the capacitors directly behind it on the back side of the board. They should all ready about 500-600 ohms or so. If the chip has failed, generally those capacitors will short out and show less than 10 ohms. If that is the case, then you will need to replace that chip.

[krustyone]

Re: LG 55LW9500 no video, no audio

Thanks for the help Nick.

The heat soak on the heatsink of IC101 provided no change.
I used a heat gun 100C (212F).

I checked the SMD caps around the HDMI chip and found no anomalies, however, I did find caps under IC101 were all reading 17 to 18 ohms.

These are all connected to the +0.9v core which feeds into multiple VDDC's AON_VDDC and AON_POR_VDD on the as well as TVM_OSC_AVDD on IC101/BCM35230.

Has anyone experienced this fault?

[nomoresonys]

Re: LG 55LW9500 no video, no audio

You might have to get it a little hotter, see if that setting easily melts a piece of solder.