LG 42PC1RV PDP42V8

[brandyman]

My LG 42PC1RV (Chassis PDP42V) started playing up about 6 months ago.

It would switch on and after some variable time it would go into standby.  Once it went to standby it would immediately try to power up again but then go back to standby.  Blue light on front would flash on and off in time with this event and also noise of relay switching on and off from PSU board.  If I unplugged the tv from the mains socket and left for some time and dwitched it back on later it would again work for sometime before once again going through this switching on/off process.

I checked all voltages on PSU board and found them not to exist.  I then removed all connectors bar the mains input from the PSU board and checked voltages again.  This time all voltages were fine.
I found that if I re-connected all leads to the PSU board except the one going to the YSUS board the voltages on the PSU board were fine.  For some reason the YSUS board is dragging all the PSU board voltages down when it is connected.

The TV has now totally failed.  Switch it on and the blue light comes on with audible noise of relay clicking but after about 5 seconds relay clicks again (presumably off) and blue light flashes at about one second interval.
There is a board below the PSU board (probably control board) that has two red LED's on it.  On switch on both of these leds light up but when the problem occurs one goes out.
If I remove lead between PSU and YSUS board and repower the tv appears to go into standby mode.  There is no relay click after about 5 seconds and both red leds remain on and blue light stays on.  I am assuming that these leds are some form of basic diagnostic.

I am of the opinion that possibly the YSUS and/or YDRV boards could bve faulty.  Any ideas?

[tv tony]

welcome to the pc1d, or one of its cousins, the drive pcb,s can be unhooked for elimination, the y sus is sus, no pun intended, but first check the z drive pcb.s can go s\c. at the bottom of the y-sus and at the bottom of the z sus are two small plugs which supply 58v and 189v to these boards, we have found the small caps that decouple these lines go short, also measure the resistance to deck from the two fuses on the y-sus pcb
good luck,
tony walker

[tv tony]

to add, the versio8 is reliable normally, are the output stages on the y-sus ic.s or full of transistors, there were two?

[brandyman]

Thank you for replying.

With all boards connected there are no voltages present on PSU.  I have unhooked YSUS board and all votlages from PSU are now normal.

Checked power connector socket on YSUS board (bottom righthand corner) and there is short circuit between VS and ground so it appears problem lies with YSUS board.  Va & 5V connections to ground are ok.

I am not quite sure when you refer to output stages being IC's or Transistors. There are a bank of 5 transistors attached to heatsink that sits directly between the two connectors that go to the YDRV board.  Three of the transistors are FDA59N25 and appear to be connected in parallel with each other.

The other two transistors are marked as follows:

W9NK 70Z
CCORP  VW
MAR 628

W9NK 70Z
CCORP VW
MAR 611

These two are not connected in parellel as per the first three.
The one marked W9NK 70Z CCORP VW MAR 611 has a short between all terminals and back to the power connectors VS treminal so this may be the reason for the loss of VS when the YSUS board is connected to the PSU.

Unfortunately I can find no information on the web about these two transistors.  Any help on these would be much appreciated.  If this transistor is the reason for the failure and I could source a replacement it would be preferable to complete board change.

I was going to replace the board but was getting conflicting information.
The board has a white label attached and also etched information as follows:

White Label
6871QYH948B
PD42069J032075

Etched
LGEPDP 051124
MODEL:  42V8&X3
PART NO:  6870QYH105B

I was given compatible boards as:
6871QYH053A
6870QYH005B
6871QYH953A
6870QYH105B
6871QYH048B

I was then subsequently told by another source that none of these were compatible.  Stange given that The part number etched onto the board appears in the list of compatibles.

I am really at a loss as to what to do.  If I could get a replacement for the unkown faulty transistor I would try that.  If I can not then I guess it will have to be a board change.  But which board given the conflicting information.

Any help would be much appreciated.

Thanks