60PB5600 no picture

[Srtech]

I am just learning about Plasma and LCD/LED TV's and have an LG 60PB5600 that turns on but no picture or menu. It does power up with a white screen flash. The blue indicator light on the front of the set flashes when I press the menu button, but no menu appears on the screen.

The vs and va voltages are according to the label as are all voltages on the connector to the main board. (RL_on =3v)

After reading other posts, I tried getting the test patterns but no success. I jumpered EXT_AUTO_GEN, unplugged the blue ribbon from the main board, unplugged P231 from the main board and jumpered RL_on to 5.2v. Then plugged the set in and turned it on, but all I got was flashing green LED on the control board.
At first it was three short and one long pattern. Now it is four long flashes.

Where do I go from here? Thanks for sharing your knowledge.

[Hamie]

Re: 60PB5600 no picture

Pictures of the boards?

Need to check vsc and Vy test points on the ysus.

[Srtech]

Re: 60PB5600 no picture

Ok so here are a set of pictures.

Measurements are vsc on P152 is at 235.7 vdc, and vy on the test point is 85.4 vdc.

[Srtech]

Re: 60PB5600 no picture

Ok, so after looking at the other messages on this tv, I did more checking.

Voltages on y-sus board at P152 connector are:
Vpp = 235.2v
Vsc = 235.2v
5vf = 90v
Sus_on = 85v

On P151 at pin 7 there is "15vf" = 100v

Va on the power supply = 54.7v and the same on the z-sus board.

I checked the four igbts Q401, Q404, Q405 and Q406 and none are shorted but test as diodes.

So should I be looking at a Main Board? I have white screen flashes at power up, and sound is working, just no picture or menus.

[Srtech]

Re: 60PB5600 no picture

In addition Imchecked the following voltages at the power supply connector P813

M_on = 3.06v
RL_on = 3.1v
5.2 = 5.2v
17 = 17v

AC_on = 5v
17v_det = 2.5v
VS_on = 3.07v
vs_det = 2.5v

[Hamie]

Re: 60PB5600 no picture

Remove buffer and recheck vy and vsc.

[Srtech]

Re: 60PB5600 no picture

I am not sure where vy is accessible as I don't see a clear identification on the y-sus board.

However at GR 170 = 84.7v
And at GR250 = 271v, since they are marked as vy - and vy+ respectively, I assume vy is the difference of 187v. It is the same with the buffer disconnected.

With buffer connected vsc = 235.3v measured at P152, but with the buffer disconnected vsc = 0v at P152.

[Hamie]

Re: 60PB5600 no picture

No

black probe to -
Red probe to +

[ReeceyBurger123]

Re: 60PB5600 no picture

No

black probe to -
Red probe to +

Good patients bud lol

[Srtech]

Re: 60PB5600 no picture

Ok the vy voltage reads 187v DC and is the same with both buffers disconnected.

[Srtech]

Re: 60PB5600 no picture

Like this?

[Hamie]

Re: 60PB5600 no picture

Edit:

OK y-sus is probably OK.

When you first turn on the tv do you get a brief flash of the screen? Or does it always remain pitch black?

[Hamie]

Re: 60PB5600 no picture

Do you see where the top buffer connects to the bottom buffer. (white flat cable)

There are some smd capacitors, can you tell if any are shorted?

[Srtech]

Re: 60PB5600 no picture

Yes I get the flash (prime as I have learned)

[Srtech]

Re: 60PB5600 no picture

Yes I see three caps and measure two at 0.01uf (shorted I assume) and one at 35uf. One is blown apart also!

[Hamie]

Re: 60PB5600 no picture

No probs, check those smd caps, that may be your only problem and you can fix this for practically nothing.

[Hamie]

Re: 60PB5600 no picture

Too quick for me.

No for this test put your meter in ohm.

See if they are low resistance.

I'm pretty sure the top one should be 4uf.
Can't remember though I'll need to check.

[Srtech]

Re: 60PB5600 no picture

Sounds good Hamie, thanks for spending some of your evening on this. What values should those smd caps be?

[Srtech]

Re: 60PB5600 no picture

So for resistance two are open (C873 & C975) and C956 measures 5k.
C873 is broken also.

[Hamie]

Re: 60PB5600 no picture

Yeah I though it was just your photography that c873 is actually split in 2!

The other 2 are probably OK.

OK so change it out, give me few minutes I need to get the exact value.