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Old 04-15-2015, 08:28 PM   #1
BrynDN
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Default LG 50PV450 goes black after a few seconds

I have a LG 50PV450.UA manufactured October 2011. It was recently affected by a power surge which damaged the cable box it was connected to. It has the following symptoms:
1) Standby power works fine (LED lights once plugged in)
2) Main power works fine (TV responds to remote and boots to image, briefly)
3) After disconnecting it from AC power for around 30 minutes and reconnecting the display works fine (all menus display in accurate color with no lines on the screen). It responds to all remote control commands. It reads a USB memory stick and displays a JPEG image in full color/clarity.
4) After about 30 seconds to 1 minute, the display turns to very narrow green horizontal lines which are bouncing/scanning or goes completely blank.
5) About another short period of time it seems to go completely black - no image is displayed, though the LED indicator indicates that it is responding to remote commands. One time it came back on normal after a few more seconds and briefly displayed the menu and the "No Input Detected" message that hops around the screen.
6) Remote still works fine. Power off still works fine and goes into standby. When powering back on the image remains black until the power is disconnected for an extended period of time. If disconnected for a short period I did notice that the screen powers on with either brief green lines and once showed the source information box with a few narrow black lines through it for a couple seconds, then went fully black.

Any ideas what board I should try first? Based on the closest other threads I can find, I'm leaning towards YSUS but this will be my first plasma repair so not really sure. Anything I could check with my DMM to confirm the problem?
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Old 04-15-2015, 09:21 PM   #2
capkid
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Default Re: LG 50PV450 goes black after a few seconds

If the cable box was damaged, the TVs main board may also be toast. You can try running test patterns to see if you get anything onscreen. To run test patterns:

(1) Unplug TV.
(2) Disconnect the LVDS cable that runs from the control board to the main board.
(3) Jumper locations labeled R51 and R52 on the control board with a paper clip.
(4) Plug in TV then turn on.

Service manual is here: http://www.toms-service-manuals.com/...&mfg=LG-Zenith

Last edited by capkid; 04-15-2015 at 09:23 PM..
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Old 04-16-2015, 12:41 PM   #3
BrynDN
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Default Re: LG 50PV450 goes black after a few seconds

Quote:
Originally Posted by capkid View Post
If the cable box was damaged, the TVs main board may also be toast. You can try running test patterns to see if you get anything onscreen. To run test patterns:

(1) Unplug TV.
(2) Disconnect the LVDS cable that runs from the control board to the main board.
(3) Jumper locations labeled R51 and R52 on the control board with a paper clip.
(4) Plug in TV then turn on.

Service manual is here: http://www.toms-service-manuals.com/...&mfg=LG-Zenith
Thanks so much! All test patterns work fine (full grey does cause a faint humming sound) and since main board is disconnected and images appear correctly (no artifacts, dim spots or lines) I assume the main board is the culprit?

If so, any advice on repair of that board? Just replace? It seems it works, at least for a little while. I can pull up the menus and access USB content. Of course it's the most expensive board, so would like to exhaust repair options before buying a new one, but the service guide doesn't seem to even give troubleshooting steps for this board
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Old 04-16-2015, 02:14 PM   #4
capkid
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Default Re: LG 50PV450 goes black after a few seconds

You can do other tests on the YSus, ZSus and PSU, but the main board is most likely faulty based on your symptom description. They are generally only repairable by the average DIY'er in rare instances (e.g. Vizio LCD voltage regulator replacement). It might be a long shot or not cost effective, but you can check with Modus Link about a repair: http://www.moduslinkptstvboards.com

Last edited by capkid; 04-16-2015 at 03:38 PM..
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Old 09-20-2016, 07:45 AM   #5
scapapas
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Default Re: LG 50PV450 goes black after a few seconds

I had a similar problem. I replaced the control board and now during the boot up I am farther in the process.

When I try to jump the input from the LVDS with connecting R51 and R52 the following happens..

1) Only top half of the screen works. (Think problem with the Y Driver lower board)
2) Gets half way through the sequence then stops.

I believe this is being caused from a short somewhere on the Y-SUS board. When I try to measure the Vsc and Vy voltage during the boot up it is way higher than the Vsc and Vy recommended. I can't use the voltage adjusters to get it with in the limits.

Therefore I am thinking, I have a bad voltage regulator somewhere on the Y-SUS board. I can not find the schematic drawing of the Y-SUS to try to diagnose. But I have been using the training manual.

My question is; do you guys think just replacing the Y-SUS will fix all the issues or do you think I should just order the Y Driver lower and this should be replaced at this step?
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