LG 50PA6500 no picture

[jagu3090]

Hello, I have an LG 50PA6500 Plasma TV, purchased new on June of 2012.

I am willing to climb tall mountains to get this plasma TV fixed since the picture on this TV has been absolutely gorgeous and this is a 1080p (not a 720p).

I have an old-school Tektronics dual trace 60Mhz scope (if it comes down to that.)

When I connect the power cord to 120 VAC I get two relay clicks from a black relay RL103 located near the bottom edge of the PSU. When I turn the TV on (either with remote or hard power button) I get one relay click from the same relay.

Also, when I turn it on it gives two red power LED blinks and then nothing. No picture, no sound, no ability to set/adjust settings or select inputs since the screen is dark.

This TV had a problem when it was around 6 months old. LG sent a mobile service van to fix it and they changed a board. This TV has a power PC board that is “refurbished,” so I am thinking the LG guys replaced the power board at that time.

Without disconnecting anything from the PSU (PN=EAY62609701) I am getting the following voltages from the PSU:

VS = 200-206 / actual = 204,
VA = 55 / actual = 54.9,
M5V = 5.2 / actual = 5.16.

From another PSU board connector with thinner wires:

17 / actual = 17.24,
5.2 / Actual = 5.20,
ERROR CORRECTING 5.2 / actual = 5.20,
STBY / actual = 5.20,
RL_ ON (AC_DET) / actual = 2.54,
M_ON (AUTO GND) / actual = 3.29.

When I turn the TV on, the MAIN (input) board (PN=EAX64280504) has a solid LD500 RED LED.

The CONTROL (PN=EAX64290701) has D101 GREEN LED with LONG-SHORT (pause) LONG-SHORT. These four blinks (including the middle pause) is then repeated as a pattern.

I have removed the Y-SUS, Z-SUS, and PSU boards. Gave these three boards an inspection for cold solder joints. “Push tested” with my finger looking for loose solder joints. Gave all diodes an in-circuit front-to -back ratio check. (Diode D256 on the Y-SUS tested shorted in-circuit, but out of circuit it tested ok; there is a 2.2 ohm resistor in parallel with this diode.) Tested all power MOSFETs on these three boards for self-shorts or shorts to ground. Between these three boards there are a total of four fuses and they are all ok.

Visually inspected all visible electrolytic caps in this TV for bulging or leakage, they all look ok.

Visually inspected all visible resistors in this TV for any sign of overheating, they all look ok.

Visually inspected all visible power MOSFETs in this TV for any signs of overheating, they all look ok.

There are voltage potentiometers on the Z-SUS and Y-SUS boards, but I do not know where these test points are located nor what values of voltages to look for. NOTE: I HAVE NOT MESSED WITH THESE VOLTAGE POTENTIOMETERS AT ALL!

I have the CONTROL ext_auto_gen test through-points bridged with solder and wire and the ribbon from the MAIN to CONTROL disconnected at the MAIN, but all of the symptoms are exactly the same: two red power LED blinks, same repeating pattern with the CONTROL D101 green LED. (However, LD500 RED LED on the MAIN has no activity.)

Thank you, and lets keep these PLASMA TV sets alive!

[jagu3090]

Re: LG 50PA6500 no picture

I have been able to locate the VY and VSC voltages on the Y-SUS. VY is available cross R272 and VSC is available across R273 (both resistors are 220k Ohm 5%).

VY / actual = bouncing periodically between 25 and 27 VDC per analog VOM.

VSC / actual = bouncing periodically around 2 VDC per analog VOM.

My DVM does not have an analog graph scale, so the digital output is garbage varying all over the place. The analog VOM is 50k Ohms/V, so the 220k resistors are now paralleled down to around 202k Ohms. Just sayin'.

I would estimate these two “waveforms” with a period of around 300 ms. I have no idea what these voltages or waveforms should be.

[jagu3090]

Re: LG 50PA6500 no picture

I have located a voltage called VZB on the Z-SUS. It is across resistor R412 (another 220k Ohm resistor) and this voltage is a rock-steady 149.5 VDC.

[jagu3090]

Re: LG 50PA6500 no picture

So now I have removed the top Y Buffer and turned my TV on. Now I get the CONTROL's ext_gen_test on the screen as it cycles through it's test patterns, but only on the bottom half of the screen.

My voltages at the Y-SUS are now:

VS = 190 / actual = 189.9
VSC = 150 / actual = 150.8

On this upper Y-Buffer board I tested for shorts from the Y-SUS connectors to the orange ribbon connectors. There are about 14 pins in a row at the topmost orange ribbon connector that are shorted. The top IC looks as good as the rest of the IC's. Does this mean my plasma screen is now toast because of the orange ribbon getting torn up? I guess I will find out.

Shopjimmy.com shows this YDRVTP board is out of stock, but they also have this to say about it:

(replace YSUS and YDRVBT also!)

DO NOT REPLACE THIS BOARD WITHOUT ALSO REPLACING THE YDRVBT AND YSUS BOARDS! If you replace this board alone it will fail again.

Does anybody know what this is all about?

[nicholas1110]

Re: LG 50PA6500 no picture

Hi, this model is known for the ribbon cable tearing and shorting on the sharp metal edge. If you remove the front trim on the tv you can inspect the top ribbon for tears. If it is torn it’s not worth trying repair the tv. The top buffer ic chip will short due to this tear. Inspect the ribbon closely before trying a replacment board. Hope this helps

[jagu3090]

Re: LG 50PA6500 no picture

@ nicholas1110:

Okey dokey. Thanks for the tip!

The top two or three orange ribbons are intact! Where the ribbons may contact the metal there is a soft black felt like material glued on the metal. So you can say I consider myself to be very lucky.

To be able to perform this check you first have to remove one screw at the top-middle, from the back side of the TV. (Took me a while to figure this out). This screw has an arrow in the metal pointing at it.

I can either attempt to solder a new chip (PN R2A20299FT) on the YDRVTP board or I can replace the top Y-buffer board. Has anybody had any luck with used Y-Buffers? I know ANY board I get (be it new or used) I will be testing for shorted ICs. My guess is that shorted ICs is about the only way these Y Buffer boards become defective.

I have not unsoldered or soldered chips with this many small leads, but there is always a first time. So I will see what parts are available and at what cost. (My preference is to simply replace the Y-buffer.)

[ajshoe]

Re: LG 50PA6500 no picture

I'm pretty sure I have the buffer boards for this set. where are you in Ky ?

[jagu3090]

Re: LG 50PA6500 no picture

@ ajshoe

I am in South Central Kentucky, near Bowling Green. The board with the blown chip is the top Y-buffer board YDRVTP with these two part numbers:

EAX-64300101 REV 1.1
EBR-73763902

The bottom Y-buffer appears to be functional and this YDRVBT has these two part numbers:

EAX-64300301 REV 1.1
EBR-73764302

[jagu3090]

Re: LG 50PA6500 no picture

This morning the two Y buffer boards (YFRVTP & YFRVBM) arrived from Good Point Recycling; Middlebury, Vermont. Their prices are hard to beat (ebay, $29.99 + tax, free shipping). Both boards passed a continuity test for shorted ICs. Installed the top YDRVTP only, since I know the bottom board is working.

BEAUTIFUL PICTURE ! You can't beat these old 1080p plasma sets for image quality. I am a happy camper.

As a reference I have the following voltages of this working set without any input video:

PSU:
VS = 205 VA = 55.1

M_ON = 3.29 AUTO_GND = 0 these are available on 18 pin connector P183
RL_ON = 2.53 AC_DET = 4.11
STBY = 5.20 STBY = 5.20
GND = -4 mV GND
GND = -4 mV GND
5.2V = 5.19 ERROR_DET = 0.583
5.2V = 5.19 5.2V
GND = -4 mV GND
17V = 17.25 17V

YSUB:
(R272) VY = 189.9 (R273) VSC = 150.5 R272 / R273 are located on the leftmost edge of YSUB, tophalf
ZER_COM = 99.9 Available on connector P131, top right corner (same as ERC on ZSUB)

ZSUB:
(R412) VZB = 149.4 R412 is located below the smaller connector P131
ERC = 99.1 available on connector P131 (same as ZER_COM on YSUB)

If there is video on the screen then VY and VSC will not be steady but rather jumping around (and not really measurable with a Digital VOM) but centered around 190 and 150 volts. VZB will also be jumping around a little bit (not much).

This set is going back up on the wall. Thanks everybody for reading.

[kca]

Re: LG 50PA6500 no picture

jagu3090 ~

I read through your entire post and I have an LG 60PA5500 that has the exact same symptoms that yours did. The only difference is that when I brought it home 2 days ago and turned it on for the first time it worked flawlessly and did so the majority of that day even though I turned it on and off about 5 times. But, then it went black and has been that way for the last 36 hours or so. Like I said, it is exhibiting the exact same signs/symptoms/behaviors as yours, down to the Green LED blink pattern and the Red light on the Main Board. I baked the Main Board and that had no effect. I also tried the EXT_AUTO_GEN bridge and still nothing on the screen.

What I haven't yet done is disconnect the UPPER (or LOWER) Y-Buffer Board(s) from the Y-SUS and tried to diagnose it from there like you did. The reason being, it worked flawlessly just a couple of days ago and I would rather not mess around with the orange ribbons if I don't have to.

Can you think of any other step or course of action I could or should take before dealing with the buffer boards?

Thanks, in advance, for any help you can provide.

~ kca