LG 50PV450 no video

[jb_gt_84]

Hello all,
I have a LG 50PV450 Plasma TV that was given to me. The manu date is 11/2011.
It has audio but no video. The Vs, Va and 5V from the SMPS look OK. On the Y-SUS board, the Vy- signal jumps to approx -190V then decays back to -25V at a 800ms duty cycle. So I figured the Y-SUS board was bad and replaced it. However, I still get the same results. I removed the Y-BUF boards and now see a steady signal on the Vy (-190V) and Vsc (150V) per the unit label. So are the Y-BUF boards bad? I'm thinking I should replace them as a set, correct? Thanks in advance for your help.

[tom66]

Re: LG 50PV450 no video

You can try isolating one board at a time.
Usually with bad Y-buffers the voltage will be low immediately, I'm not sure if going low after some time indicates a fault or just a control board shutting down.

[jb_gt_84]

Re: LG 50PV450 no video

So finally got y driver boards and installed them.
I now have a picture! But it's not very good!
Am I correct that the Z-SUS is bad based on the pixelation?
The bottom half also looks like the y-driver is bad, but it's a new board as is the Y-SUS. Could the previous bad y-driver have damaged the Y-SUS or did I get a y-driver or Y-SUS that was no good?
Thanks!

[freakaftr8]

Re: LG 50PV450 no video

Disconnect lower y buffer board and try with just upper in place.

[jb_gt_84]

Re: LG 50PV450 no video

The lower y driver has a ribbon cable and 2 plugs that connect directly to the Y-SUS.
I found a service training manual for this TV and it says not to operate the Y-SUS if the ribbon cable is removed, but the y-driver is plugged to the Y-SUS. If I remove the lower y driver, I don't have that ribbon connection to the upper y driver, so it seems this is something I should not try?

[freakaftr8]

Re: LG 50PV450 no video

Yea your right. Can only operate with lower y buffer in place. Sorry for that. Just tried with an lg set I have and it's all mal discharge if you do that since no data will be received to the buffer. Well it almost looks as if your lower buffer is acting up. Did you purchase these buffers from a cracked screen TV?

[jb_gt_84]

Re: LG 50PV450 no video

The y driver boards came from ShopJimmy.
They say they are new.

[tom66]

Re: LG 50PV450 no video

On the back of the plasma panel module inside, there will be part number, like PDP52T8000, what is written on yours?

[jb_gt_84]

Re: LG 50PV450 no video

Pdp50r30111

[freakaftr8]

Re: LG 50PV450 no video

That's 720p. Listen closely. Any ticking coming from the ysus?

[jb_gt_84]

Re: LG 50PV450 no video

I hear a hum from both the Y-SUS and Z-SUS but not a ticking.

[jb_gt_84]

Re: LG 50PV450 no video

The label on the monitor shows 150 for Vsc but it's pegged at 144.5V

PS I have borrowed a scope for the weekend.

[jb_gt_84]

Re: LG 50PV450 no video

Looking at the signals on the 4 plug connectors between the y-sus and y drivers I see the following:
On the top expected 10.9VDC and saw 10.8VDC. On the other 3 connectors, I expected Vscan as 107VAC (~350Vp-p). On the middle 2 connectors, Vscan is a steady ~140VDC and only on the bottom connector do I see a waveform similar to that shown in the training manual. I removed the y drivers and saw the same signals.
So shouldn't I see the same Vscan on all 3 connectors? (Input was none - static on screen)
(y-sus is from paylesscomponents and was listed as new.)