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

[Rogue110]

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

Hi,

I found this forum and it seems similar to my issues, but I am having one trouble after the next.

So it started when we were watching tv (near the fireplace) and heard a crack and the picture went out. Completely dead and no standby light. I opened the TV up and found a capacitor (not a bulk but a small ceramic) damaged as though it had popped as well as the fuse was bad. I tried replacing the cap and the fuse, but same issue. So I replaced the power supply. The new power supply worked fine and was not blowing, but the standby light would randomly come on if I plugged power in, and sometimes would not come on until I unplugged power. If I pressed the power button when the standby light was on, the standby light would turn off, but nothing else. So I replaced the main logic board.

So the new logic board is in and the tv will power up, but only with sound. Volume on the remote and power commands work, but sound only. I have tried unplugging YSus and ZSus, but exhibit the same failure of sound only. None of the heat sinks on the Y or Z sus get warm while the tv is on. For the measurements requested earlier I am getting:

(1) PSU: VS (204V) and VA (54V)
(2) YSus: VSCAN (0-8V)
(3) ZSus: VZB (72-78V)

I also tried the EXT_AUTO_GEN short and this did not create a picture. The screen is not cracked, but I am starting to wonder if there was some sort of large scale issue that took out multiple boards and the screen itself. Any thoughts??? Time to give up?

[capkid]

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

Nice. Glad it's working again.

[SurrealMustard]

Fixed!

Just to provide some closure here, after mainboard replacement, the television is now working. Hooray!

Thanks everyone for the tips. Hopefully my mistakes will help someone else who might have the same problem.

[tom66]

Re: Sustain

If the board was okay, what could've been the cause of the unstable readings? Could there be a meter issue?

Main board could be turning panel on/off causing that, or perhaps your Y-sus was bad before but the replacement is ok? (two boards could be bad, e.g. power surge damage.)

[SurrealMustard]

Sustain

As long as the patterns look ok your Y-sus is almost guaranteed to be ok.

If the board was okay, what could've been the cause of the unstable readings? Could there be a meter issue?

[tom66]

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

As long as the patterns look ok your Y-sus is almost guaranteed to be ok.

[SurrealMustard]

Repair

Yeah, that's one reason Tom and I mentioned checking the control board earlier in your thread - to avoid just throwing parts (money) at the TV. It appears that there are a couple variations of the main board. Which one do you have installed? Someone here may be able to help you find one at a good price.

So even with the test pattern being displayed properly using the paperclip trick, I could still have a bad Y Sustain?

Main boards are definitely LG's Achilles heel. Otherwise they're not too bad for reliability.

And they're a bit on the expensive side too.

[tom66]

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

Main boards are definitely LG's Achilles heel. Otherwise they're not too bad for reliability.

[capkid]

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

Yeah, that's one reason Tom and I mentioned checking the control board earlier in your thread - to avoid just throwing parts (money) at the TV. It appears that there are a couple variations of the main board. Which one do you have installed? Someone here may be able to help you find one at a good price.

[SurrealMustard]

Misdiagnosis

Here are some instructions from Tom. A paperclip would be an OK jumper: https://www.badcaps.net/forum/showpo...01&postcount=8

Nuts, I wish I would've seen that before I replaced the Y Sustain. The paperclip trick not only yielded a picture with the new sustain board, but with the old one as well. And yikes, are those main boards ever expensive!

[capkid]

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

Here are some instructions from Tom. A paperclip would be an OK jumper: https://www.badcaps.net/forum/showpo...01&postcount=8

[SurrealMustard]

Part

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.

How would I go about doing the Ext Autogen procedure that was mentioned there? I replaced the Y sustain and am getting the same symptom (power, screen lights up, nothing on the screen). This time, the VSC is holding steady at around 140-145 though.

[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.

[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.

[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]

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.

[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]

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

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]

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?