LG Plasma VZB at half required voltage

[mpwjak]

LG 60PA5500 no picture but has sound.
YSUS board voltage bad and upper buffer board shorted.
Replaced all three; VSUS, upper and lower buffer boards.

TV worked fine for ~3weeks, then no picture again.

Looked at VZB voltage and see 65v, should be 120.
Adjustment moves from ~63 to ~66 only...

Any experience with this? please reply with a potential component fix.

Thanks!

PS - I spent several hours looking through threads but didn't see this issue, my apologies if I missed it.

[mpwjak]

Re: LG Plasma VZB at half required voltage

Also to note; The 65v measured is with out the VSUS board connected.

[mmartell]

Re: LG Plasma VZB at half required voltage

I don't know about this model in particular but some zsus boards receive a +5v from the ysus so I would measure again with allboards connected.

[Andrew F. Ali]

Re: LG Plasma VZB at half required voltage

Measure the Vs with the Z-SUS jack unplugged and see if it returns to 165Vdc. If not unplug the Vs from the Y-SUS Bd and see if it returns to 165Vdc. Yes, as mentioned by mmartell 5Vdc generated by the PWR Bd goes to the Z-SUS Bd via the Y-SUS Bd. See if you are getting that. Where is the Va voltage, to the X-Drive Bds at the bottom, coming from the Z-SUS Bd or the Y-SUS Bd or directly from the PWR Bd?

[mpwjak]

Re: LG Plasma VZB at half required voltage

Well... I received "New" YSUS, upper and lower buffer boards and powered it up. Immediately heard the upper buffer board making noise, crackling... Powered down the unit and prepared to test voltages. Powered back up and VS and VA were good - upper buffer continued to crackle a bit - VBZ was ~175V (Spec is 120V on this TV). I was able to dial it back to ~140V but that was it.

The upper board actually sent a small puff of smoke out as it fully expired. Testing showed it was indeed shorted - I suspect it came to me this way. YSUS board -VY is at spec of 185V but the VSC is way low at ~40V, (Spec is 150V on this TV).

At this point I can't test anything except power board outputs and they are all good.

Questions:
#1 Is it possible to blow a board if the potentiometer is cranked completely over when I order new YSUS, ZSUS, upper and lower buffer boards? Is there a best known method to avoid this?

#2 Is it correct that no pins on a buffer board should short to the outputs where the ribbon cables connect? (I'm having some difficulty seeing the 'Pins that are connected together' from the testing videos.)

Thanks for the help!

[mpwjak]

Re: LG Plasma VZB at half required voltage

Questions:
#1 Is it possible to blow a board if the potentiometer is cranked completely over when I order new YSUS, ZSUS, upper and lower buffer boards? Is there a best known method to avoid this?

#2 Is it correct that no pins on a buffer board should short to the outputs where the ribbon cables connect? (I'm having some difficulty seeing the 'Pins that are connected together' from the testing videos.)