LG 47LC7DF-UB No video issue

[UsAndThem]

Hi, I have been lurking around the site for a while reading posts and searching to try and avoid members having to repeat themselves but I've finally decided to register and begin participating. I am hoping that you all might have some insight into isolating the source of the issue I'm having with my tv. I believe I have narrowed it down to the power supply or main board but would like some ideas on how to confirm it. To start I apologize for the long post. I am hoping to get as much of the meat and potatoes out on the table to minimize the back and forth with little stuff.


The TV is a LG 47LC7DF-UB.AUSLLJM which, when turned on with no devices plugged in would display a “no signal” image which scrolled around the screen. I then turned the tv off and plugged my PS3 through the component jacks. Upon startup, the red led turns to a green flashing led for approximately 5-10 seconds then to a solid green indicating "normal" operation. The green led blinks when a command is issued from the remote. The backlight does illuminate at power on and stays on but the on–screen menu/ images do not display. I repeated this test with various inputs, all with similar results. Next I unplugged everything and the “no signal” image returned. Although not usually advisable, I plugged in my PS3 with the tv still powered and the attached image is what I observed. It's the menu screen for a Blu-ray movie in my PS3. There are three horizontal bands with different shading and a small single horizontal row of lighter gray (same as the next higher band) pixels just below the half-way point on the screen.
At that point, like many others, I opened up the back of the tv expecting to see bulged/leaking capacitors but all the caps in the power supply appear good visually. After reading on here that some caps will test badly even though they look good I started measuring the power supply voltages.

Main board number: EAX32740501
Power board number: EAY3281690

The following are the voltages measured (in Volts) at the corresponding connectors

Connector P202
(off/on)
ACD 5/5
PWR-ON 0/2.9
5Vs 5/5
GND 0/0
I-C 0/2.9
ERR 0/.6
BRI 0/.3
5Vs 0/5
GND 0/0
PWM 0/0
6V 0/6
GND 0/0
3.4v ON 0/2.4v

Connector P201
19v 0/18.2
19v 0/18.2
G 0/0
G 0/0
6v 0/6
G 0/0
3.4v 0/3.3-3.4
G 0/0
12v 0/11.7
G 0/0

Connector P200
3.4 0/3.4
3.4 0/3.4
G 0/0
G 0/0
6 0/6
6 0/6
G 0/0
G 0/0
12 0/11.7
12 0/11.7
G 0/0
G 0/0

Connector P205 and other inverter connectors
24v 0/23.9 (x5 pins)
G 0/0 (x5 pins)
BRI 0/.3 (x1 pin)
I-C 0/2.9 (x1 pin)

Connector P701 - same voltages as P202
Connector P702 - same voltages as P201

Connector P703
G 0/0
G 0/0
led g /2.4
led r /0
G /0
5vst /4.9
g /0
IR /4.1
G /0
Key1 /3.2
G /0
Key2 /3.2

Connector P700
9v /8.9
Eye /.2
G /0
Rin /0
G /0
Lin /0
G /0
Cvbs /0
AV /0
Y-sw /2.1
G /0
C /0
G /0
Y /0


I will post up some hi-res board images shortly. Thanks for the help,
Brian

[retiredcaps]

Re: LG 47LC7DF-UB No video issue

Hmm, interesting mix of capacitors. United Chemi-con KY are good while anything with the name Capxon are utter crap.

If you gently flex the sides or top and bottom of the TV frame, does the picture look perfect?

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I'll have to put the boards in, power it up and see if I can get an image to return so I can try flex the frame. Are you thinking the panel could be bad? Prior to measuring the voltages, I re-flowed the current capacitors to ensure there were no cold joint issues and since then, I haven't been able to get the menu or an image back...only a blank screen. Regarding the existing capacitors, I already have a replacement set on order for the CapXon ones in case thats the problem. Either way it could be one in the future so better to fix it before (hopefully) they cause any other component damage.

[retiredcaps]

Re: LG 47LC7DF-UB No video issue

Are you thinking the panel could be bad?

It might be tab bonds. Search for "tab bonds" here and you will see many issues with TVs in the 46 to 52 inch class. I'm not sure if yours is affected, but something to check. Some people report that bumpers have fixed, but for how long, we don't know.

I have a Toshiba TV that suffers from bad tab bonds, but so far I haven't worked on it yet.

[tom66]

Re: LG 47LC7DF-UB No video issue

Since you get the NO SIGNAL display have you tried getting the service menu up and seeing if that appears OK? Hold MENU on TV and MENU on remote at the same time.

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I was able to get the service menu up and the menu itself looks fine although the horizontal banding is still there. I also noticed that a ghost of the previous menu will remain. I have only been successful at getting the "NO SIGNAL" condition after I leave the TV unplugged for an extended period of time. If I have the "NS" condition and cycle the TV, all I get is a blank screen.

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I also tried flexing around the edges of the bezel and observed no changes in the image behavior.

[tom66]

Re: LG 47LC7DF-UB No video issue

And the problem - no picture - occurred at the same time as getting horizontal banding? The main board is most likely the issue, but the horizontal banding is very weird...

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

The banding does not occur when the screen is blank. There appear to be two states. One, An image is visible with the horizontal banding and two, when there is no image and the screen is solid black(one even shade), but illuminated.

[tom66]

Re: LG 47LC7DF-UB No video issue

It might simply be that the banding doesn't appear against a black background but is really always there. Do you want to troubleshoot the main board, or just replace it? It could be something like the EEPROM being corrupted, which removed some "region brightness" settings.

In the service menu can you select ADJUST DATA and see if there is anything on there, such as RESET?

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I am willing to try and troubleshoot the main board until it no longer becomes feasible (lack of equipment, skills etc.) . I'll look in the ADJUST DATA menu for a RESET or similar option.

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I was able to get into the ADJUST DATA menu but there didn't appear to be a reset option. After looking through the menu and sub-menu options I cycled the TV and the blank screen conditioned returned. With the blank screen, I held the menu button on both the tv and remote. I did observe the screen brightness increase after holding the buttons for 10 seconds or so. It appears that the tv can still be controlled, volume up/down, channel change, etc. even when the tv is in the blank screen condition

[tom66]

Re: LG 47LC7DF-UB No video issue

Under the other options there could be a RESET or CLEAR option - can you check under them too?

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I checked under all available menu's and sub-menus. I can take pictures of each if that will help determine if there are any useful menu options

[tom66]

Re: LG 47LC7DF-UB No video issue

If you can that would be helpful.

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

I have attached some images of the 1st level of the service menu. I have sub levels photographed and can upload as necessary. Let me know if you see anything you want me to try. I also included some test screens.
Brian

[tom66]

Re: LG 47LC7DF-UB No video issue

Darn - I was hoping to see a RESET option, but no dice. I suppose there might be one in the normal user menu - have you tried that? I also don't think it's a coincidence that the banding on the top stops exactly where the checkerboard pattern changes.

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

There is a picture reset in the users menu but I have tried that and it has not shown any change. Is there a chance that the main board could be re-flashed with the correct epk or other file. Do you have any opinion on whether the voltages measured at the power supply I listed are appropriate? I am inclined to think there may be a fault somewhere on the main board but I realize my intuition doesn't really mean much when it comes to the way the board functions.

[tom66]

Re: LG 47LC7DF-UB No video issue

The voltages look good to me. It might be possible to update the firmware, does this TV have a USB port? If so maybe it will work with some firmware from LG's website.

[UsAndThem]

Re: LG 47LC7DF-UB No video issue

The tv has both a usb and a rs-232 port