Power, but no video on LG 60PN5700 Plasma flat panel

[SurrealMustard]

Here's what I've got: 1 LG 60PN5700 60" plasma television that seems to power on normally (you can even see light output from the screen if you look closely) but displays no video. The back has been removed from the set and a visual inspection of all the boards reveals no obvious issues. The small green light on the board in the center occasionally blinks while the television is on (I'm guessing this is what it's supposed to do).

Any ideas on what might be the problem or what the next step for troubleshooting might be?

[capkid]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

It sounds like it could be a ZSus issue. You'll need to start by checking for the standard voltages - there should be labeled test points on each of the boards:

(1) PSU: VS and VA
(2) YSus: -Vy and VSCAN
(3) ZSus: VZB

Please post clear pics of the circuit board layout if you need further guidance.

[SurrealMustard]

Measurements for the LG Plasma Television

It sounds like it could be a ZSus issue. You'll need to start by checking for the standard voltages - there should be labeled test points on each of the boards:

(1) PSU: VS and VA
(2) YSus: -Vy and VSCAN
(3) ZSus: VZB

Please post clear pics of the circuit board layout if you need further guidance.

On the power supply board, VS is at 200 and VA is at 55.
On the Z sustain, neither VZB1 nor VZB2 registered any voltage.
On the Y sustain, D Vy1 and 2 didn't seem to register anything at all either. VSC seemed to go off the chart on the multimeter no matter which connector I measured from - it just put "1" on the screen like it does when you're in too low of a range for the voltage that's being measured.

All measurements were taken using the metal on the TV's framework as a ground.

[capkid]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

It doesn't sound like you took the readings correctly.

VZB should be taken by simultaneously placing the negative probe on the negative test point and the positive probe on the positive test point, not using the chassis as ground.

The VSC reading on the YSus is taken in the same manner as VZB. Can you take a picture of the -Vy test point on the YSus?

[tom66]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

If Capkid's tests are ok, the next step will be to jumper the EXT AUTOGEN points to see if you can get good test patterns.

[SurrealMustard]

trouble points

It doesn't sound like you took the readings correctly.

VZB should be taken by simultaneously placing the negative probe on the negative test point and the positive probe on the positive test point, not using the chassis as ground.

So you're saying that I should be putting one lead on VZB1 and the other lead on VZB2? I don't know how well it'll work because the pins are so close together, but I can give it a try.

The VSC reading on the YSus is taken in the same manner as VZB. Can you take a picture of the -Vy test point on the YSus?

The VSC will present the same challenge, but I'll give it a look. Here's the connection on the Y board where I was testing the Vys (you've gotta zoom way in on the writing on the left, but it's there):

[tom66]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

I think you're misunderstanding. VZB is a test point on the Z-sustain, and it's usually marked across a resistor on the Z-sus board. Similarly, -VY and VSC are also marked on the Y-sustain. They are not the labels next to the connector coming from the control board.

[SurrealMustard]

I see

I think you're misunderstanding. VZB is a test point on the Z-sustain, and it's usually marked across a resistor on the Z-sus board. Similarly, -VY and VSC are also marked on the Y-sustain. They are not the labels next to the connector coming from the control board.

So I will not be finding or measuring these values on any connector, that clears it up a bit. I'll have to take a second look at it to see if I can find the correct locations of those points.

[SurrealMustard]

The board

Upon further inspection today, I was unable to find those points. Here's some photos of the boards:

Z:





Y:

[capkid]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

I've attached annotated pics. I can't see the -Vy on the YSus. Can you take a picture of the label on the back of the panel that lists the voltages? Also, please include a pic of the back of the TV with all the boards visible.

Edit: It looks like your boards are different from the pics I posted, but the test points should be in similar spots.

[SurrealMustard]

Follow up with proper voltages and pictures

I've attached annotated pics. I can't see the -Vy on the YSus. Can you take a picture of the label on the back of the panel that lists the voltages? Also, please include a pic of the back of the TV with all the boards visible.

Edit: It looks like your boards are different from the pics I posted, but the test points should be in similar spots.

Thanks, the points were right in front of me the whole time and I missed them somehow. The correct VZB reading is about 113 and the VSC fluctuates between 154 and 174.

Here are the pictures of the entire set and the sticker with the voltage information:

[tom66]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

Wow, I think this panel may not use -Vy or may use some alternate drive method, as it's not marked? Really odd.

[SurrealMustard]

Onward

Wow, I think this panel may not use -Vy or may use some alternate drive method, as it's not marked? Really odd.

In that case, any idea what the next troubleshooting step would be?

[capkid]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

Wow, I think this panel may not use -Vy or may use some alternate drive method, as it's not marked? Really odd.

Yeah, I scanned the pics closely, and I saw no -Vy. Very different.

It looks like the VSC is having issues. I'd turn the TV off, unplug it, disconnect the Y-buffers from the Ysus, then turn the TV back on and recheck VSC.

Note: If you go to reconnect the Y-buffers to the YSus after the above test, wait about 10 mins. before doing so. The high voltage caps on the YSus need time to discharge.

[SurrealMustard]

Buffer question

Yeah, I scanned the pics closely, and I saw no -Vy. Very different.

It looks like the VSC is having issues. I'd turn the TV off, unplug it, disconnect the Y-buffers from the Ysus, then turn the TV back on and recheck VSC.

Note: If you go to reconnect the Y-buffers to the YSus after the above test, wait about 10 mins. before doing so. The high voltage caps on the YSus need time to discharge.

Because of the way the Y buffers are connected to the Y sustain, would it be better to disconnect them by means of unscrewing the Y sustain and letting it hang around unplugged from there or would it be better to do it some other way?

[capkid]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

Unscrew the boards.
Disconnect buffer from YSus.
Screw YSus back onto chassis.

[SurrealMustard]

VSC Voltage without the buffers connected

With the buffers disconnected from the Y Sustain, I'm getting just a few volts on the VSC. It's ranging from 0 to 30, but mostly hanging around the mid teens.

[tom66]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

So, just to check, the white connectors are fully out? If so, this would indicate a bad Y-sustain, to me.

[SurrealMustard]

Confirmation

So, just to check, the white connectors are fully out? If so, this would indicate a bad Y-sustain, to me.

Yup.



Actually, now that I look at it again, the voltage fluctuates more like between 50 and 115, sometimes varying depending on what angle the leads are at.

[capkid]

Re: Power, but no video on LG 60PN5700 Plasma flat panel

I agree with Tom: Looks like a bad YSus. I'd try the logic control board test that Tom mentions in post #5, just to cover all bases. The logic board is the small one in the middle of the panel.