LG 60PK750 Plasma loud buzzing blown panel?

[corellian]

Guys and gals,

basically I'd like to know if it's possible to electrically kill your plasma panel removing internal cabling with it still connected to mains? It's a PDP3R10000 panel btw.

BACKGROUND

This unit was working except for the HDMI ports. I confirmed again via disconnecting LVDS and jumpering test points on Control board - test image displayed fine.

Upon starting to disconnect the main board in an attempt to reflow the BGA chip, I disconnected the cable coming for the PSU board to the mainboard as shown in the pic. To my surprise (not realizing mains power was still connected) the TV turned itself on but with a loudish buzzing.

I unplugged the mains and didnt worry about it for the time being. After I did a dodgy reflow effort with flux/heatgun, put the mainboard back in and connected everything back up the same buzzing continues and theres no image. Even when trying the test mode!

The buzzing is not localized to any area but seems to be everywhere. The troubleshooting I've tried is tightening every earth screw and disconnecting Z and Y-sus. With the YSUS disconnected the buzzing goes away but that's probably due to the panel not being energized?


I don't mind if the panel is fried, at least then I can scavenge the other boards (except for mainboard) and move on to my next learning experience!

[Unspun01]

Re: LG 60PK750 Plasma loud buzzing blown panel?

Why would you suspect a damaged panel?

It is more likely that you damaged the Y-Sustain board by plugging/unplugging live. Test for shorts on any heatsink mounted IGBTs or MOSFETs.

Could be a bad YDRV board (upper or lower) that is shorted and the YSUS is laboring to supply the short and then you get that buzzing until protection shuts the TV down.

[corellian]

Re: LG 60PK750 Plasma loud buzzing blown panel?

Why would you suspect a damaged panel?

It is more likely that you damaged the Y-Sustain board by plugging/unplugging live. Test for shorts on any heatsink mounted IGBTs or MOSFETs.

Could be a bad YDRV board (upper or lower) that is shorted and the YSUS is laboring to supply the short and then you get that buzzing until protection shuts the TV down.

Thanks for your post Unspun01.

I was thinking a panel issues because I could not localize the source of the buzzing. However, upon a quick check disconnecting YSUS from top and bottom Y buffers the buzz remained. Only with the YSUS d/c the buzz goes away. Protection isnt kicking in as the unit isnt turning itself off.

I will pull YSUS and check for shorts, cold solder joints etc., when I get home tonight.

[corellian]

Re: LG 60PK750 Plasma loud buzzing blown panel?

I was wrong about disconnecting the YSUS makes the buzzing go away. Only by disconnecting Y and Z-sustain does the buzzing go away. As this video demonstrates.

https://1drv.ms/v/s!At2_QJcZ3njMjiDSnw3FtlNklpwb

[corellian]

Re: LG 60PK750 Plasma loud buzzing blown panel?

I gave up on finding this fault (no picture, loud buzzing). Stripped the unit of its boards and tossed the panel.

For the record i couldn’t find any shorts in the YSUS and all voltages from PSU were normal and it wasn’t shutting down into protection. There was just a loud buzzing even when the Z and Y sustain was disconnected from the buffers (so not a panel issue). The loud buzzing went away when disconnecting signal cable between control board and YSUS, so assumed there was a fault in either of those. Couldn’t find it in the YSUS (or PSU) and i thought I found a bad cap in CRTL but by pulling it out to test I ripped a pad. The cap tested fine out of circuit so thats when I chucked in the towel!