LG 50PS60 Half Screen

[jfcurran]

Hi,
I came into a discarded LG 50PS60. This morning, when cold, the TV put out a good HD picture from a Chromecast attached to HDMI 4.

But about 30 minutes later the upper half of the display went dark except for the odd multi-color sparkle or single horizontal line. Eventually, the entire screen goes dark. But audio continues throughout. After a little while, the TV does seem to lock up.

Does this point to any specific failure?

Thanks for any advice!
Jim

[rash.m2k]

Re: LG 50PS60 Half Screen

Tcon board fault? I noticed on my tv (Phillips but shares components with hisense) if I pull one cable from tcon to panel exactly half the screen goes black,try pulling one cable at a time and see what it does

[Biruslapio]

Re: LG 50PS60 Half Screen

This is a plasma, there's no T-CON, this is some fault with upper buffer board or some connection to it, remove the top Y-buffer and test for shorts on the output pins.

[jfcurran]

Re: LG 50PS60 Half Screen

Thanks folks - I will check those connections.

[jfcurran]

Re: LG 50PS60 Half Screen

Removed the upper buffer. Could not find any shorts (watched several Youtube videos on the topic).

Inspected Y-Sustain board for heat issues, bad solder joints - found none but did not look under the wide rubber strips. Any advice on removing them?

After replacing all boards I powered it up and the bottom half showed the Chromecast bootup and the upper half showed random lines and specks. But eventually the set would go black. Subsequent toggling on and off just yielded a bit of a flash and then darkness.

The Y-Sus board made quite a buzz but I had not replaced all the screws. Pressure on the board quieted the buzzing but it came back when I let go. The buzzing seemed to stop at the same time that the display stopped showing the bottom half.

Any ideas?

[Biruslapio]

Re: LG 50PS60 Half Screen

When the upper buffer is removed, the TV should work always on with half picture without shutting down.

[aaronwt6]

Re: LG 50PS60 Half Screen

Removed the upper buffer. Could not find any shorts (watched several Youtube videos on the topic).

Inspected Y-Sustain board for heat issues, bad solder joints - found none but did not look under the wide rubber strips. Any advice on removing them?

After replacing all boards I powered it up and the bottom half showed the Chromecast bootup and the upper half showed random lines and specks. But eventually the set would go black. Subsequent toggling on and off just yielded a bit of a flash and then darkness.

The Y-Sus board made quite a buzz but I had not replaced all the screws. Pressure on the board quieted the buzzing but it came back when I let go. The buzzing seemed to stop at the same time that the display stopped showing the bottom half.

Any ideas?

You should never run any of the boards with even one screw missing. Asking for further damage. Those are all ground points for the board.

[jfcurran]

Re: LG 50PS60 Half Screen

OK I will try that. But it looks like signals travel through the upper to the lower? See ribbon cables in the photo.

Thanks,
Jim

[Biruslapio]

Re: LG 50PS60 Half Screen

This board has this extra flat cable, don't know what signal it carries, worst case there will be no image on the bottom half and it will light up but only black will be shown.

The cable too carries the signal for upper/lower buffer and if it's damaged or dirty can cause this effect.

You need to put all screws back, this is why the buzzing was stopping when you pressed on the board, poor grounding, they must be tight too.

Measure the SMD ceramic capacitors on this upper buffer, anything with too low ohms(<200) without any exact value resistors in parallel with those capacitors may be a bad IC.

[jfcurran]

Re: LG 50PS60 Half Screen

OK - upper buffer board removed; all screws in tight.

Here's a photo of the Y-Sus board driving only the lower buffer board (upper board removed).

I still need to test the capacitors on the upper buffer board. Will get back with that.
BTW - while this image was displaying, the wirewound resistor on the Y-Sus board got *really* hot. The odor is what got my attention. I have not smelled that since I have been working with this TV.

Once the set went back to flickering to black on power-up, the resistor started to cool.

I still need to measure the capacitors.

Thanks,
Jim

[Biruslapio]

Re: LG 50PS60 Half Screen

This resistor goes in series to the buffers, so it is drawing an abnormal amount of current, test the lower buffer output pins too.

Did that resistor heat up this much with the upper buffer connected? Maybe it's a bad idead on this specific model to do that, some older plasmas had this problem.

[jfcurran]

Re: LG 50PS60 Half Screen

Hi,
No the resistor was cool while running the upper only.

I tested across the obvious capacitors on the buffer boards - all the same resistance. I also checked voltages on the power connectors - these checked out as well on both boards. During these tests, the set was in its original failure mode (lower display working, upper dark, streaky, speckled)

Also took the YSus board out and looked very carefully for bad solder joints (this time I removed the insulating strips). Nothing wrong that I could see.

Am wondering if I can safely put a scope on the drive signals for upper/lower to trace them across the YSus board? Don't have a schematic.

Jim

[Biruslapio]

Re: LG 50PS60 Half Screen

I have a training manual thanks to elektrotanya, it helps a lot with pinouts and voltage readings, your problem is upper or lower buffer, or some connections, the logic board should output the full image always, you can try doing the AUTO_GEN test but this looks more like a buffer related fault.

[jfcurran]

Re: LG 50PS60 Half Screen

So, to summarize the current behavior.

On a cold start (TV off for several hours, below-average room temperature), the TV shows the bottom half of the image as depicted in the photo.

After a few off/on cycles, the screen just flashes and stays blank.

While the bottom half is working, the waveform at the buffer boards even/odd test points is about 400V peak-to-peak.

While the set is blank, the waveform is about 40V peak-to-peak and it looks more like logic signals than analog. Again, this is for both the upper and lower boards.

Could the upper board be creating a failure that takes out the whole picture or is the Y-Sus board bad and the upper buffer bad as well?

I was not really successful using the external sync pin on the control board to get a stable view of the waveforms but I did see the voltage difference quite clearly.

Thoughts?

[Biruslapio]

Re: LG 50PS60 Half Screen

Test VSCAN and -VY when both buffer boards are fully connected, if any voltage is floating and not stable I call upper buffer is bad.

[jfcurran]

Re: LG 50PS60 Half Screen

-Vy stable at 180V; VSCAN unstable. I will look for an upper buffer board.


Thanks!