LG 50PX2DC-UD No picture/sound

[raider08]

I'm new to the site and i'm trying to diagnose a problem with a LG 50PX2DC-UD plasma I acquired for free and see if its worth fixing. I'm not too sure where to start, I've read plenty on this site but still kind of confused where to start.

I acquired this TV for free from a friend because when you plug it in and press the power button the standby light flashes green twice then returns to the red solid standby light.

I've taken the back of the TV off and checked the fuses, all test good on my fluke meter. Then checked for obvious blown capacitors, none of the caps appear visually bad. Nothing else appears wrong on the boards.

I guess I have to test the voltages but not too sure where to start. I'm very good with my meter and understand circuit board basics. Thanks

[raider08]

Re: LG 50PX2DC-UD No picture/sound

I did some more reading and tried unplugging the y and z sustain. The Z sustain(right side?) made no difference. Unplugging one of the y sustain(left side) made the green light continue blinking indefinetly. I unplugged both connectors one at a time (circled in yellow and pink in the photo) and the connector circled in yellow made the difference, the pink one made no difference.

Also are the two boards i circled in teal are those the buffer boards(upper and lower)? Thanks

[raider08]

Re: LG 50PX2DC-UD No picture/sound

No advice on what to do next? I cant find a service manual for this tv online..

[raider08]

Re: LG 50PX2DC-UD No picture/sound

After Some More Research, I Checked Voltages On The Power Supply. On A connector Going To The Y Sustain Board, I Get 0 Voltage On Both The Vs And Va Pins.

Also Like Mentioned Before If I Don't Have The 4 Wire Connector (Labeled- 5+/5+/Ground/Ground) On The Y Sustain Unplugged The TV Returns To The ReD Standby Light. When Unplugged It Flashes Green 16 TImes Then It Turns Solid Green.

What Else Should I Check To Find The Problem? Thank You

[raider08]

Re: LG 50PX2DC-UD No picture/sound

Pictures

[Alastair E]

Re: LG 50PX2DC-UD No picture/sound

Check for shorts on the IPM's....

[dkneyle]

Re: LG 50PX2DC-UD No picture/sound

If you have unplugged the y-sus and z-sus supplies, and the power supply doesn't appear to come to life in some way, then you'd have to suspect the power supply is still the cause. I've just managed to get a similar model going, and my first option was to exchange the power supply. But no joy - it was the Y-Sus board. Just check - with the z-sus power lead disconnected, do the fans run continuously? If so, I reckon your power supply is good. The Y-Sus board on these is notorious for failed IPM chips, which some people can change over, but I found it easier to excahnge the board. Also, just check the two 10 ohm SMT resistors at the bottom of the Z-sus board (near a bunch of electros). For some reason they go open circuit as well. Let me know how you go.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

i Will Check Those Things When I Get Home Tonight.

I Know I Have Never Seen the Fans turn On, But When I Unplug Only The Z Sustain Board It Won't POwer On, It Will Go Back To Standby.

I Will Return With My Findings Hopefully Tonight.

I Appreciate The Help You Guys Provide For Rookies Like Myself..I'm Trying To Learn What I Can, Still Have A Long Way To Go To Understand How Everything Works Together.

And Sorry For The Capital Letters, When I Post From My Phone It Does It.

[dkneyle]

Re: LG 50PX2DC-UD No picture/sound

I've had a good read through your thread, and whilst the behaviour is slightly different at switch on, I still would put money on it being the Y-Sus board. If you remove the upper power connector from the power supply to the Y-Sus board then the power supply should try to start, and fans begin to run. It detects no feedback signal ("something wrong" it says) and shuts down. The Vs and Va do not come up because the power supply is in protection-mode. Regarding the Y-Sus board, you're lucky. Coppel Repairs can check your Y-Sus and repair it for a fixed price. (As can others.) The end result is that you have a board that is as good as new. The problem with a secondhand Y-Sus is that the IPM chips already have some age on them. (I had to use a secondhand board unfortunately.) It seems that the IPM chips have a finite life. Also check those 10 ohm resistors I mentioned. Yes, you have correctly identified the Y Buffer boards. Mine were good, and there's a bit of mucking around to get them out, and you risk damaging the ribbon cables or not putting them back in correctly. (I had a single pixel-width horizontal line due to having pulled out the buffer boards for checking. Solved by cleaning and reseating the connector.) You can do a rough check on the buffer boards by diode-testing the power supply tabs (where the screws connect the pads to the Y-Sus board.) If you don't get an indication of a short then I'd be tempted to leave well enough alone. (I stand to be corrected by those more knowledgeable.) Looking at your photos, it is pretty much the same set as mine. I have a spare power supply, but I suspect that your's doesn't need changing out. Have fun with the set. It's a great feeling to see that picture come up when it does.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

Just Got Home. I Unplugged The 4 Wire Connector On The Y Sustain Board ThaT Way The Tv Wouldn't Go Back To StandbY, Then Unplugged All The Connectors On The Z Sustain. The Fans Never Turned On At All.

I Looked At The Two Resisters AT The Bottom Of The Z Sustain and visually They Look Good.

[dkneyle]

Re: LG 50PX2DC-UD No picture/sound

Regarding those 10 ohm resistors (the code on them says 100), mine looked perfect, but when I removed them they were open circuit. I assume you have a meter to check them? In circuit I got a reading of ~40k (must be the circuitry around that point).
You do realise that the power for the Z-Sus piggybacks through the Y-Sus board? When I was doing my tests I simply left the 4 lead connector from the power supply to the Y-Sus board in place. Above that one I removed the bigger connector that supplies Va and Vs. This removes the high voltages from Y-Sus and V-Sus. I would plug in, and even without pushing any 'on' button, the fans would start running continuously. I notice that there are some tell-tale LEDS on the signal boards beneath the power supply.
Do any of these come on? Especially when V-Sus and Y-Sus and disconnected from power.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

Ok, I will unsolder those two resistors and put my meter on them.

This morning i tried unplugging that connector and the fans never turned on. I have also during my previous troubleshooting tried unplugging certain connectors and I havent seen the fans run ever.

Also I have never seen any other LEDs light up or flash, the only one would be the standby light.

I will check those resistors and report back. Thank you for your help.

[dkneyle]

Re: LG 50PX2DC-UD No picture/sound

I wouldn't unsolder those resistors - too hard to put back on again if they are OK. Just put your meter across them in circuit. They are in parallel, giving 5 ohms.
You are getting close to the point of having to bite the bullet and decide which item you are going to changeover to see if you get life back into the old girl. That's why I was suggesting using one of these Repair services. If the board is good they will tell you and only charge for the cost of diagnosis. I'd be sending off that Y-Sus board if I was you.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

Too Late, I unsoldered One Side Of The Resistors Before I SEen Your Reply. They Have No resistance.

Before I unsoldered Them I Had Put My Meter On Them.. one Was Reading In The Millions Of Ohms and The Other Was In The Thousands Of Ohms. So Now I Have To Replace Them. Are These Resistors Something You Can Get At RadioShack?

Once I Replace Them, I Will probably Send My Ysus TO Get Repaired Like You Suggested.

[dkneyle]

Re: LG 50PX2DC-UD No picture/sound

Well, it certainly sounds like you are going down a very similar path to that which I travelled. That might be good because it means you can get this TV going again hopefully. I used regular 1/2 W 10 ohm resistors that can be bought from places like Radioshack. You'll need to dress the leads so that they match the pads for the SMT resistors. I put a decent blob of solder onto one pad, then solder one lead to that. Once cool, the other lead is easier; position and solder. Do the same for the second. Check that the exposed leads aren't fouling anything else. Then send off that Y-Sus board. You know how to access Copel Repairs? Do a Google search - easy. I'm looking forward to hearing the next installment. Removing the Y-Sus board looks more challenging than it is. I actually had my driver boards out at the time. Not sure if this is absolutely required. With those boards removed I was able to negotiate the board out to the left and then tilt the lefthand edge toward me and it came out. I think you can probbaly do that with the driver boards in place. The secret always is to go slowly, if something feels tight don't push or pull it too hard; you are probably caught up on something. Ahh - those resistors in your photo aren't the ones. R9,R91 10ohm 0.5W SMD resistors. Bottom left near a bank of electro capacitors.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

Crap..I've Never Seen A Resistor Like That, The Ones In The Picture Are More Like What I'm Used To Seeing.

I Measured The Correct resistors Like You Explained And I Got 5.8Ohms.

I reChecked Those Resistors That I Unsoldered And They Were Both Like 47.5K Ohms. I Will Find A Chart Online To See What They Are supposed To Be. If They Are Good I Will Just solder Them Back.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

Ok, I looked up the resistor and I found it is a 47k and a 5% tolerance. So I will just resolder them back to the board.

Now something I was wondering.. if i had the outgoing connectors unplugged from the power supply and powered the tv on, if the power supply was working properly wouldnt I have the correct voltages at each pin? Or would the power supply somehow sense there is a problem and not put out any power to the ysus/zsus/etc?

[dkneyle]

Re: LG 50PX2DC-UD No picture/sound

Without the status feedback from the boards plugged into the power supply it will protect itself and not fire up the high voltages. People with more knowledge than me know how to put in a link between the feedback line and the output so that it will start up, but without a circuit diagram I'm out of my depth. The fact that you are getting some sort of life out of the power supply i.e. the led indicators on the front panel come to life, suggests to me that the power supply is OK and it is shutting down (or staying shut down) to protect itself. I'm very inclined to that Y-Sus board being your problem.

[raider08]

Re: LG 50PX2DC-UD No picture/sound

That makes sence, I remember reading somewhere that you can jumper certain pins and make the power supply power on fully.

I emailed coppel about repairing the ysus, just waiting on a reply.

[CoppellTVRepair]

Re: LG 50PX2DC-UD No picture/sound

Just to add for those curious with the case: we (Coppell TV Repair) received the YSUS board referenced in this case and it tested out fine.

It's fairly rusty, but it worked in our set.

So the hunt continues.

It bothers me that disconnecting YSUS from +5V makes the set stay on.

Can you then turn it off at will?

You do not have the YSUS board now and without it the ZSUS board could not be connected.

You say that the TV comes on and stays on.

Can you , then, try to supply signal to one or more of the inputs and then flip through the sources (be it with a button on the case, be it with a SOURCE/INPUT button on the remote) until you get audio out of the set?