LG 60PX950 ~ Vertical Pixelation Issue

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

DC Voltage ~~ With Power Applied:

Tested this resistor in question (Red, Red, Gold Gold) again for voltage just now, and got a reading of 5.5 when I set the DMM all the way down to 200m. A 005 reading on 2000m, as expected, and no DC readings were present above that.

Was that the expected DC result on a resistor that is rated for only 2.2 Ohms?

The Ohms reading was still at 4.8 when the probes were placed one way, and then still an almost negligible reading when the probes were reversed.

[cliff_hootarski]

Re: LG 60PX950 ~ Vertical Pixelation Issue

NEVER measure resistance with power applied! (May destroy your meter).

Measure voltage either across the component or with respect to ground.

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

Okay. I'll refrain from doing that moving forward.

So, if I am getting all of the correct resistance readings on all resistors on the Y Main when the power is not on, AND I am getting 150V on the Vs and -180 on the -VY (which are correct) when the power is applied and the Y Buffers are both disconnected, then does it ONLY make sense that it is another component (and probably a capacitor?) on the Y Main that is defective?

[attainteddragon]

Re: LG 60PX950 ~ Vertical Pixelation Issue

as a general rule, if you are getting all of your voltages on your y-main with the buffers disconnected and then missing some with buffers fully hooked up, then it will be either the buffers or panel dragging it down.

if you tested your buffers correctly and they are ok, then hook them up without the panel attached to it. if your voltages are still present, then the panel is causing the fault.

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

Okay. I will try that as a last measure.

I don't think the panel is at fault, because I was getting the top half of the screen to show up flawlessly just a few days ago. It only failed after i put the replacement lower Y-Buffer in.

This may be important: When I first installed the replacement lower Y-Buffer, and paired it with the original, working upper Y-Buffer, I did not hook up either one to the YSUS. I was going to check the voltages on the YSUS first, and then my plan was to reconnect the Upper and if that was okay then connect the lower as well. One at a time, if you will, and with the power completely shut off and the set unplugged each time for a few minutes so there were no power-related/capacitance issues.

When I first powered up the set, with both buffers still DISconnected, I got a pattern of green vertical lines running down the middle of the screen that was unlike anything I had seen before. There were three, I think, "patches" of green running up and down, each about 4 to 6 inches thick. I only left it on for a few seconds, knowing it wasn't what I was looking for, by quickly powering the set back down with the remote control.

Is it possible that I did some damage to one of the components on the YSUS by powering up the set without either of the buffers connected? Damage in the sense that it might have created a surge that pushed one of the components beyond its limit?

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

Additional info:

1) With no power applied, the Ohm reading on the Vs resistor dropped from 59 with neither Y-Buffer connected (both disconnected, in other words) to 43 as soon as I hooked up either buffer. Not sure if that conveys anything in a definitive way, or is that a normal response when the power is not in play?

2) I put the DMM in Continuity Mode and tested all of the resistors on the YSUS. Most had continuity (beeped), a couple did not, and one (and only one) ~ the Vy resistor ~~ displayed a reading. It was precisely 476. What does that mean? Seems very odd. The only connection I could make was that I was getting the same readings in the 470 - 480 range when I was testing all six of the the Y-Buffer diodes (three found on the lower and three on the upper). However, this reading on the Vy YSUS resistor was obtained when the YSUS board was taken completely out of the tv and tested in another room, and no diode could be found near it on the YSUS itself.

Any thoughts?

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

I should mention too, that the reading of 476 on the Vy that I cited in the last post was only present when the probes from the DMM were a certain way. The black had to be on the bottom resistor leg and the red on the top (as it sits vertically on the board).

Stranger yet.

Does this indicate a failure of some sort?

[attainteddragon]

Re: LG 60PX950 ~ Vertical Pixelation Issue

you are most likely getting slight variations from other components in the circuit. if this happens, lift a leg from the component and recheck. it will now give you an accurate reading since it is no longer in the circuit with other components potentially interfering with your readings.

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

New info:

The panel seems okay because I took off the ribbon cables from both upper and lower (per atd's suggestion up in Post #84) and still obtained the low and fluctuating voltages measured on the Vs resistor and Vy resistor.

This would seem to strongly indicate that the problem is with the buffers themselves, but I still doubt that.

Why?

Because I tested the buffers again, this time very extensively, looking for the actual readings on the DMM on every pin and not just testing for continuity (beeping). Result was that both the old (original) lower buffer and the new lower tested exactly the same. Every single pin, which I tested separately and carefully one at a time, returned readings of between 968 and 988. Almost all of them were right around 980. There were two pins on each board that did not register, but they were the exact same ones on both boards and upon further inspection I realized that they were not connected to the circuitry per plan of the designer.

So, I seem to be stuck in this loop:

Either the buffers are defective (both the upper and the lower now, though neither appear not to compromised per my testing), and I would have to spend more money to get new ones and would likely get the same malfunction result re: the Vs and Vy voltages

OR

There is a component (or, components) on the YSUS that is (are) causing the Vs and Vy voltages to be drawn down .... but only when either one or both of the Y-buffers are connected.

When the YSUS is not connected up with the two Y-Buffers, I do get the expected VS = 150 and Vy = -180 every single time I test.


QUESTION:

Is it possible, therefore, that the Y-Buffers are okay, but when connected to the YSUS these buffers call for power and voltage that the YSUS is not capable of delivering because the YSUS is still compromised in some way? Does it sound like a capacitor issue?

Has anyone ever seen that happen?

[Hamie]

Re: LG 60PX950 ~ Vertical Pixelation Issue

I'd say what's probably happened is you've bought a dodgy buffer from someone and it's now blown your previously good top buffer.

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

That's what I am afraid of, Hamie. It seems to be the case.

But, how do you account for no continuity readings on the Y-Buffers, and the consistent readings on all the pins? Couple this with all six of the diodes reading the same on both buffers and I'm just not sure dropping $100 on buffers will solve this.

Have you seen buffers you've worked on in the past test so flawlessly and yet be defective?


{What I am concerned about, of course, is that if there is a flaw on the YSUS that it will most likely blow out any new buffer or buffers I put in there.}

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

Did another test, but need some feedback to see what it means:

Wanted to see how far these 150V Vs voltages I am getting travel toward the buffers. So, I left the "wire-designed" connector between YSUS and Y-Buffers in on the YSUS side and pulled it out on the buffer side. Please see pictures below.

I did this on both upper and lower, one at a time. With each test, the alternate buffer was disconnected.


Results were puzzling:

I expected to either get the full 150V at the connector level, or get the low and fluctuating readings I get whenever the buffers are fully connected up.

Instead, I got a steady reading of 51 on both the upper connector, and then on the lower connector too. Not 151 ..... just 51.

I measured these off of the wires themselves that form the bridge between YSUS and each Y buffer.

Can someone tell me if that is a normal occurrence? Maybe someone can take a similar reading off of one of the tv's they are working on to see if the voltage drops by 1/3 at this connector level if the buffers are disconnected on the buffer side of the connection bridge and therefore are out of the picture.


{Note: I just decided to leave both connectors connected to the YSUS at the same time, but both disconnected on the Y-Buffer sides. Wanted to see if these 51 readings were "split" or affected in any way. The answer was no. They both read 51 now, simultaneously. So, the 150V readings at the Vs resistor level are somehow being translated into 51V, and that "full" 51V is being supplied to both connectors.}

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

I think I found out what happened.

I tracked down a Training Manual for the LG 50PK950, which is a close enough model to mine for this purpose.

When I first bought that replacement lower Y-buffer board and installed it a few days ago, I left both of the wire-designed connectors between the two buffers and the YSUS in on the buffer sides while I reattached the YSUS itself. Did this, in part, because the YSUS overlaps and sits on top of both of the buffer boards when it is screwed back on, so I put the buffers on first, then plugged the wire connectors into the buffers, and then finished the re-install by screwing the YSUS in on top of the buffers.

I did not hook up these wire connectors to the YSUS at that precise moment in time, as I thought I would check the Vs and Va coming into the YSUS from the power supply one more time along with the Vs and -Vy resistor voltage readings once again before hooking up the buffers.

Apparently this was a big mistake.

If you look at the pictures below, it specifically says NOT to remove the right-side (the YSUS side, in other words ~ labeled as P117 and P118 in the diagrams below) of this wire connectors while leaving the buffer boards themselves in, as that will cause the boards to fail. This explains why both the replacement lower and the original upper (which had been producing the top half of the screen on the picture) both seemed to fail at the same time.

Has anyone seen this before? I'm going to buy two new boards armed with this information. I'm documenting it here for others to benefit from and to ask if anyone has any more insight(s) or information I should know about before installing the new boards. This time, I will make sure both connectors are indeed connected to the YSUS in full before firing up the set again. Or, as an alternative, hooking up one buffer board at a time but making sure that the other buffer board is completely removed from the scenario.

Note: Apparently, one should not disconnect the left side (P109 on the upper and P209 on the lower) of the wire-designed connectors either, as the problem with these buffers failing seems to related to the FG or Floating Ground lugs between the YSUS and buffer boards. See the last picture in the sequence below to see what I mean.

Here is a link to the entire manual:

https://cdn.badcaps-static.com/pdfs/...3442af9b32.pdf

[kca]

Re: LG 60PX950 ~ Vertical Pixelation Issue

I ordered the new buffer boards. But, am still confused as to what really is wrong with the old ones. I have tested them in every way I can think of. Nothing appears wrong.

Does anyone know what is the likely result on these Y drive buffers when the floating ground is in play but the connector is not hooked up to the YSUS? What is likely to "go"?

I am hoping that they still might be fixable.