LG 50PA5500 No picture. Has sound.

[Fletch]

I have had the mentioned LG plasma TV for about 15 months now. Yup, barely 3 months out of warranty. I go to turn it on the day after my LG blu-ray player updated before powering down (most likely a coincidence) and I only have sound and no picture. No glow of any kind.
Control board D101 (green LED) flashes long-short-long-short-pause.
The EXT_AUTO_GEN jumper test does not provide any test image.
Power board, VA = 55.1 VS = 206.3
All known fuses passed continuity. No swollen caps, burn marks, visable discolorations or component leakage.
ZSUS hums. YSUS hums with a faint constant (3-4 times a second) clicking.
With no plasma TV repair experience other than what I've really read here I'm guessing YSUS board (hopefully) or PDP (not hopefully).

Any and all information and recommendations would be greatly appreciated.

Thank you

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

Check your sustain voltages:

Y-Sus: VSC, -Vy <---There should be two resistors near the edge of the board that are labeled VSC and -Vy (locations R273 and R272). Place your leads according to the + and - markings to check each of the voltages. Note: This is based on a EBR73763201 Y-Sus. If your Y-Sus is different, your test points may be in a different location.

Z-Sus: Vzb (Zbias) <-- Resistor @ location R412 based on EBR74306901 Z-Sus. Again, if your sustain is different for some reason, the location may not be the same.

Z-sus read at 151.0
Y-sus couldn't make up its mind in either location, constantly varying in value...
The boards are the same #'s

[capkid]

Re: LG 50PA5500 No picture. Has sound.

Is there a change if you disconnect the logic control board from the Y-Sus?

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

After disconnecting the control board I get -73mV to -83mV at VY and 0.2mV at VSC.

[capkid]

Re: LG 50PA5500 No picture. Has sound.

Hmm. It sounds like your Y-Sus is shot, but you may also have a bad control board as a secondary point of failure. Check your Y-buffer chips for damage (small pin holes or burns).

I've attached a pic of the panel voltages you should be seeing.

Edit: I'd probably replace the Y-Sus (or repair it) and see what happens from there.

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

I checked over the control pcb with a magnifying glass but didnt see any signs of damage. Are you at all familiar with the LED flashing codes for the logic boards?
It reads long-short-long-short-pause when the power is on.

[capkid]

Re: LG 50PA5500 No picture. Has sound.

Yeah, I'm not sure what those flashes mean. I'll see if I can find some info. Tom might know.

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

Got a new Ysus and control pcb on order. The pair is costing $50 including shipping. I should get hem between tuesday and thursday of this week. I'll chime in once they're installed with some results.

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

Replaced both Ysus and control boards. The only difference now is I get a short-short-long-short code from the control board...

[capkid]

Re: LG 50PA5500 No picture. Has sound.

Are your voltages the same on the Y-Sus as they were prior to the swap?

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

With the control unplugged:
VY 0
VSc 0

When plugged in its still 'cycling' voltage. no constant value:
VY 0 to 19.76v
VSc 0 to 12.12v

[tom66]

Re: LG 50PA5500 No picture. Has sound.

Without the buffer board is it any different?

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

There is basically no voltage showing after disconnecting from the buffer boards. 0.2mV max at any of the resistor / control cable positions.

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

Is there a viable test for LG plasma buffer boards?

[tom66]

Re: LG 50PA5500 No picture. Has sound.

Since the voltages are cycling on your Y-sus without the Y-buffer in place, I think the Y-sus you have is faulty. Your old one had steady voltages right? Or were they unstable?

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

they were also unstable on the previous pcb

[tom66]

Re: LG 50PA5500 No picture. Has sound.

Do they flash in time with the LED on the control board?
For the connector going to the y-sus from control board there is a legend on the control board.

Please measure the following pins, black probe on chassis and red probe on the pin:
Pin 6: 5V
Pin 7: PROTECT_EN
Pin 30: Y_PRO

And on the connector from control board to main:
Pin 4: DISP_EN

[Fletch]

Re: LG 50PA5500 No picture. Has sound.

I do not see a correlation between the LED flashes on the control board and the voltage cycling on the Ysus board. Ysus Voltage cycles are steadily repetitive.

Pins measurements:
pin 6: 5.04v
pin 7: 0.002v
pin 30: 0.011v
pin 4: 3.332v

Also.... I feel a bit stupid here. I did not replace all screws when reseating the ysus board after unplugging it from the Y buffers. I didn't bother to think that there would be multiple ground planes... sorry.

Voltages while unplugged from Y buffers:
VY: 190.3v
VSC: 151.1v

While plugged in to Y buffers:
VY: -0.004 to 76.4v
VSC: -0.004 to 9.2v

I'm guessing Y buffers...?

[rambo1234]

Re: LG 50PA5500 No picture. Has sound.

Here is the Service Manual for this TV... Good luck...

[tart9975]

Re: LG 50PA5500 No picture. Has sound.

Hi Guys, I am a new member so I don't have access to create a new thread. This is the thread which is closest to how my LG 50PA5500 Plasma TV is behaving, so I am posting here to get inputs from the experts here.

Symptoms: The TV just turned off by itself one time during regular watching. Now it has sound but no picture. It seems to respond and produce sound to inputs (Cable, HDMI) but without display.

I snooped around on this forum and here are the measured voltages (with a DMM):
No bulging capacitors.
Vs = 205 V (Measured at P132 Connector of YSus board)
Vy = 190.8 V (Measured at R272)
Vsc = 178.7 V (Measured at R273)
VZB = 149.8 V (Measured at R412)
Va = 54.8 V (Measured at P024 connector)
Both the Y-Buffer waveform pads show a DC voltage of 188.5,188.6 V when I connect one end of the DMM to ground screw and the other to the Waveform taps.

After running the TV on HDMI and listening to random videos for half an hour, the black heat sinks on Vsus board and Zsus board show a wee bit change in temperature (1 degree), the silver ones remain unchanged. The heat sinks on the power board heat up a tiny bit too (3 degrees).

When the TV is turned off the Vsc test point (R273) tests for a short (even by reversing the DMM leads). The VZB(R412) and Vy(R272) do not test for a short.

Pic 1: The voltage rating of the TV
Pic 2: Green Square R272, Red Square R273, Y Buffer waveform measurement points.

Any inputs would be appreciated. Thanks for reading.