LG 55PA500 does not turn on always in standby with a faint glow

[clubs07]

I have a LG 50PA5500 which has no picture no sound and does not turn on.

Keys on the TV and remote does not turn on the TV.

The red led on the corner is lit as if the TV is in standby.

There is a faint glow which is very hard to see at all times.

When I connect the ac lead the screen lights up with grey and then dissipates to this faint glow.

I had the following problems before the TV failed:

1 One of the hdmi ports failed(HDMI 1)
2 After few weeks the other HDMI port failed (HDMI2)
3 I was using the last working hdmi port successfully for another few weeks.
I put the main board in the oven at 385F-400F for 8-15 minutes few times following an advice I got to possibly sustain conductivity in broken soldering, it didn't help.
4 Couple of days later while I was watching the TV, the TV shut off. I couldn't turn it on. I unplugged it and let it stand for hours and connected back and it did not turn on.
5 Next day I plugged it again and let it stay plugged in with a faint glow on the screen for a while and it did come to life showing the lg no signal logo.
Next day when I was watching the TV it again switched off and the sound continued (which is connected to a receiver with the digital cable) for another 15 seconds and then the sound went off.

I couldn't get it to turn on again afterwards.

In my area I do get brief power outages during storms, I am using a surge protector but I don’t know if this has contributed to the TV failing.

I also remember once the TV switching off and then clicking like ten times. This was maybe a month ago and then I could switch on the TV and it never did this again.

I tried to take voltage readings from the power supply, the VS, VA, M5V, 5.2V and 17V I could get readings from all of them close to the specs written on the board. (maybe with a very little discrepancy but I am using a very cheap multimeter)

When I was using the probe to get the reading of M5V from the pin on the socket connecting to the Z board I accidentally touched the positive probe to 55V VA and M5V pins at the same time for a second and it buzzed and a little smoke came out from the probe. I then took the readings again and it didn't seem have to killed the PSU. I hope I didn’t do further damage to anything at this time.

I tried to run a test pattern using a jumper on the logic board and disconnecting the ribbon cable from the main board. The screen lighted up and showed grainy pattern allover, screen light flashing in the background etc. but it wasn’t the test patterns I have seen on youtube videos with colorful changing patterns on lg plasma TVs.

There is also the green led pulsing on the logic board, one long followed by one short and then pausing briefly and looping again.

Before the TV failed I had no problems with the picture at any time. The picture was perfect at all times until the TV failed.

I ordered a second hand logic board (since it was $10, I didn’t mind giving it a try) and today I ordered a pulled main board off eBay.

I don’t know if I am on the right track or do you guys think the problem maybe the Ysuz or PSU etc?

Many thanks in advance

[Hamie]

Re: LG 55PA500 does not turn on always in standby with a faint glow

Y-sus voltages are required.

Vsc and -vy
These are sometimes measured accross 2 resistors.

Z-sis voltages

Z-bias.

These should match your panel sticker.



When doing test patterns did you ensure the lvds cable was disconnected.

[awyatt2]

Re: LG 55PA500 does not turn on always in standby with a faint glow

best guess from what you have said would be main board.ebay is iffy may work may not just be sure it is indeed the correct board.

[Hamie]

Re: LG 55PA500 does not turn on always in standby with a faint glow

best guess from what you have said would be main board.ebay is iffy may work may not just be sure it is indeed the correct board.

He's not getting test patterns though...

Therefore, assuming he's doing the process for test patterns correctly; would indicate that the main board isn't cause for concern at this point.

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

is the lvds cable the ribbon cable connected between the main board and the logic board? I removed that cable.

I am attaching a picture of the pattern i get on the screen, and the pictures of the boards on the tv.

I don't know how I can read those voltages, I will try to find out, I would be happy if you could maybe advise me where to touch the probes on the boards?

While I tried the test pattern, that grainy image in the attachment came up again with backlight flashing etc and the tv swithced off after a minute.

The pulse I am getting on the logic board stays the same when I disconnect the cable between the Z board and the Y board. (one long, one short brief pause, not a healthy pulse probably)

Does this sound like a possible problem with the Y board?

I don't really want to bury money in this thing if it will be an expensive fix.

Y-sus voltages are required.

Vsc and -vy
These are sometimes measured accross 2 resistors.

Z-sis voltages

Z-bias.

These should match your panel sticker.



When doing test patterns did you ensure the lvds cable was disconnected.

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

i figured out how to get those readings accept z-bias

VZB 151, 152
VSC 150
VY 188-189

the sticker reads NA/ -190 / 15-V NA / 150V it doesn't specify where those voltages belong, but I guess it is inline with my readings.

I couldn't figure out where to read Z-sis yet, but I will post it once I figure it out.

Y-sus voltages are required.

Vsc and -vy
These are sometimes measured accross 2 resistors.

Z-sis voltages

Z-bias.

These should match your panel sticker.



When doing test patterns did you ensure the lvds cable was disconnected.

[tom66]

Re: LG 55PA500 does not turn on always in standby with a faint glow

VZB is Z-bias voltage (Vzbias)

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

so that is the only voltage i need from the Z board for diagnosis?

[tom66]

Re: LG 55PA500 does not turn on always in standby with a faint glow

That is one of the DC bias voltages.
The Z-sustain does a lot of other things that aren't immediately obvious, and would be best tested with a scope.
However given you got a clear pattern on the screen, it seems likely it is either a main board or control board fault (failed Y/Z does not cause those patterns)

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

thanks i ordered both off eBay. I know there is always a risk with used parts off eBay, but I will keep my fingers crossed and see if the replacement parts fixes my problem.

what concerned me was that i couldn't get the test pattern from the logic board but only that grainy pattern in the attachment. would that indicate maybe the logic board is at fault?

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

I am posting a link to the video of the pattern I am getting on the screen when I force the control board to test mode. (with the lvds cable disconnected from the control board and using a jumper on ex_auto_gen)

https://goo.gl/photos/ipHNCiXzJ3nzCf98A

Is it safe for me to assume that the Y/Z and panel are not faulty with this pattern displaying on the screen?

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

i replaced the logic and and the main boards today.

with the replacement logic board I am getting nice colorful changing test patterns. scrolling through the screen etc.

first i tried the replacement logic board with the old main board for a few seconds, and the tv didn't turn on neither from the keys on the tv nor with the remote.

then i connected the replacement main board, to the replacement logic board and the tv doesn't turn on again..

do you think the replacement main board is also broken, or maybe there was a short in the old main board which also killed the new logic board?

when i disconnect the lvds from the main board to logic board, i still get the nice test patterns on the screen.. (so that is definetely not the fault with v/z and power supply?)

what would you advise me to do?

That is one of the DC bias voltages.
The Z-sustain does a lot of other things that aren't immediately obvious, and would be best tested with a scope.
However given you got a clear pattern on the screen, it seems likely it is either a main board or control board fault (failed Y/Z does not cause those patterns)

[tom66]

Re: LG 55PA500 does not turn on always in standby with a faint glow

If you have clear test patterns then everything except the main board is working. If the TV is still stuck in standby then it is a main board fault. There is a small chance if the set turns on with a dim glow that the input section of the control board is bad, however this is quite rare. I don't think we've ever seen it on here, because it would be a really unlikely failure. You could be first.

[freakaftr8]

Re: LG 55PA500 does not turn on always in standby with a faint glow

It sounds like you have another bad mainboard honestly. I would advise trying to return the main board you got for another one.

I would also advise inspecting the ribbon cable that connects the main board to the logic board for cracks or broken connection

Also on a side note when you do get this TV figured out I would also advise you to look into trimming the plastic connectors that hold the plastic black frame to the panel on the left side looking from behind the TV near the Y sustain board. These plastic tabs are practically touching the Y sustain cables going into the panel. This model is known for those plastic tabs rubbing through the ribbon cables destroying the panel. Research other post on this forum on your model number I posted one myself.

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

thanks for your response..

then probably the main board I received off Ebay is also faulty.

I just hope the old main board didn't kill the new logic board causing that rare condition with the input section of the control board.


i tried to fix the old main board putting it in the oven etc and was concerned that i may have melted the solders more then necessary and caused a short somewhere which also killed the old logic board. (now that i found out my old logic board is also faulty since i wasn't able to get the colorful test patterns from it)


well on the other hand i should be relieved that everything else is intact. I will return the replacement main board, and order another one off Ebay or some other place. If it doesn't help I will order another logic board.

If you have clear test patterns then everything except the main board is working. If the TV is still stuck in standby then it is a main board fault. There is a small chance if the set turns on with a dim glow that the input section of the control board is bad, however this is quite rare. I don't think we've ever seen it on here, because it would be a really unlikely failure. You could be first.

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

thanks for your advice

I am returning this mainboard and will try my luck with another one.

The ribbon cable seems okay although it has some wrinkles. maybe i should change it for good measure.

Also I am going to check your post and see I how I can work out the problem with the plastic tabs, once I have this set working.

I really like the picture quality on this set and I hope I manage to fix it as soon as possible. I am missing watching movies on it already


edit.. i will try to do a continuity test on the ribbon cable and see if it is conducting properly.

It sounds like you have another bad mainboard honestly. I would advise trying to return the main board you got for another one.

I would also advise inspecting the ribbon cable that connects the main board to the logic board for cracks or broken connection

Also on a side note when you do get this TV figured out I would also advise you to look into trimming the plastic connectors that hold the plastic black frame to the panel on the left side looking from behind the TV near the Y sustain board. These plastic tabs are practically touching the Y sustain cables going into the panel. This model is known for those plastic tabs rubbing through the ribbon cables destroying the panel. Research other post on this forum on your model number I posted one myself.

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

here is what I discovered..

I have ordered this main board in the below link:

http://www.ebay.com/itm/131615468046...%3AMEBIDX%3AIT

LG 50PA5500 MAIN UNIT EAX64696604(1.1) EBT62145301


and what I have received has the following coding: LG60PA5500UG with the EBT62146301

the board has the same EAX code: EAX64696604(1.1) but different EBT#s

some websites list this board I received compatible with my tv model. but it clearly has a different EBT#.

Do you think that might be the reason the board is not working?

[freakaftr8]

Re: LG 55PA500 does not turn on always in standby with a faint glow

It's possible but doubt it. Just think you may have had bad luck with mainboards since you seem to be receiving test patterns to the screen.

[tom66]

Re: LG 55PA500 does not turn on always in standby with a faint glow

There shouldn't be any problem putting a 60" main in a 50" TV given both are 1080p, except the user menu might have a different model number stored and the energy saving features might be slightly different. It should still work.

[clubs07]

Re: LG 55PA500 does not turn on always in standby with a faint glow

thank you guys, I replaced the main board with a new mainboard I received from ftvparts.com today and my tv came back to life.

You guys were right with the diagnosis. It was the mainboard, and I was also unlucky with the replacement mainboard I received from eBay,

I think I got a good deal for a brand new mainboard for $74.99 and my tv is working as good as ever.

Now I have to future proof the tv against that ribbon cable problem freakaftr8 warned me about.