LG 50PA5500 plasma won't turn on

[easternversant]

Hi all,

This is my first foray into electrical repairs (other than some basic fixes to computers), so I'm looking for some input.

I have an LG 50PA5500 plasma television, as you know from the title. It apparently made a loud popping noise 2 months ago while I was gone, and now it won't turn on. The red indicator led is on if the tv is plugged in, but the tv won't actually turn on. When I attempt to turn it on this is what happens:

1. Indicator LED is on prior to to pressing power then...
2. Indicator LED turns off and there is an accompanying click
3. Nothing happens on screen (no glow)
4. Second click and indicator light turns back on

I have replaced the known-to-blow capacitor on the top of the power supply board, but this has not helped. I also tested it for a blown IC but didn't have any beeps from my multimeter. I've examined all the boards and don't see obvious evidence of a blown cap or fuse, but I'm no expert. Removing the upper y buffer board also does not help (the whole screen is still dark). Disconnecting either the y-sus or z-sus from power does not turn on the screen either. However, disconnecting the y-sus from power creates a weird series of noises from the y-sus board. Maybe this is because it is still attached to the control board?

Readings at the VA and VS points are extremely low, < 3 for both when measured with my digital multimeter at 200V dc. However, when I disconnect the z-sus from the power supply or disconnect the Y-sus from the z-sus I get about the right numbers if I immediately test, but I can watch the values rapidly diminishing.

All of the above leads me to believe that I have a faulty power supply board. This is actually the 2nd time I've had this occur. The TV is 3 years and 3 months old, and I just had the power supply replaced ~14 months prior.

Any ideas or further diagnostics that anyone can direct me to? I'm hoping I can fix this set as I can't replace it.

Thanks!

[Alastair E]

Re: LG 50PA5500 plasma won't turn on

Faulty/shorted IGBTs on X-SUS.

[easternversant]

Re: LG 50PA5500 plasma won't turn on

Faulty/shorted IGBTs on X-SUS.

Thanks! I have that board out now and I'm trying to test those now. I've noticed a lot of them (those attached to the heat sink) have one of the 3 prongs that doesn't indicate flow while going from the middle prong to the opposite indicates it works using my multimeter in diode testing mode. However, those are all circled on the underside of the board by the manufacturer, so I assume this is normal.

Am I on the wrong track with this testing transistors on the x-sus? Should I be checking fuses/diodes now?

[easternversant]

Re: LG 50PA5500 plasma won't turn on

OK, I have an update on this. I've now tried testing VA and VS without any boards attached (because I read something about that today). The VA reading is about right at 54.6 (55 expected), but the VS reading = 0. I assume that means a faulty supply board?

[sordids999]

Re: LG 50PA5500 plasma won't turn on

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

[easternversant]

Re: LG 50PA5500 plasma won't turn on

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

Good call, here are some pictures. Thanks in advance to anyone willing to play electronic "Good Samaritan."

The full back (with the zsus removed from the right side)


Power supply


And the z-sus. I've been testing it this evening with a voltmeter, and I haven't been able to get readings from the circled items (2 capacitors and a few little diodes).


Here is a close up of one of the offending capacitors:


Honestly, I am not sure what this all means.

[easternversant]

Re: LG 50PA5500 plasma won't turn on

Another update. I found a few things while testing various items on the power supply with the diode mode of my multimeter. A few things seemed not to work, but the most disturbing is that I got beeping from the multimeter in both directions when I tested both of these resistor boards (bottom left of the board).


I assume that at the very least these will need to be replaced, is that correct?

Thanks.

[snake91876]

Re: LG 50PA5500 plasma won't turn on

Some tvs have to have boards connected to get the vs voltage, unplugging want let you test I don't know if this is one,

[Alastair E]

Re: LG 50PA5500 plasma won't turn on

Nah--Those resistors are 0.035 ohms and will read short with meter.

All those caps circled look fine to me....

On both the Y-SUS and Z-SUS, check the pins of the connectors with the heavy cables going to for shorts to chassis/deck, Check from chassis to the Vs connections on those plugs....
They should read very high resistance. A Low reading indicates a short and that'll stop the Vs voltage coming up.
--Looking at that type Y-SUS, suspect at least 4 IGBT's have gone short....

[easternversant]

Re: LG 50PA5500 plasma won't turn on

Nah--Those resistors are 0.035 ohms and will read short with meter.

All those caps circled look fine to me....

On both the Y-SUS and Z-SUS, check the pins of the connectors with the heavy cables going to for shorts to chassis/deck, Check from chassis to the Vs connections on those plugs....
They should read very high resistance. A Low reading indicates a short and that'll stop the Vs voltage coming up.
--Looking at that type Y-SUS, suspect at least 4 IGBT's have gone short....

Hmmm, thanks for the feedback. I'll check the y-sus in the next few days, that is the one board I haven't taken off yet. I kind of suspect it is the Y-sus because it makes a little bit of noise. So I would check the VS on the Y-sus and Z-sus with the power running correct? And what exactly is meant by 'check the pins of the connectors with the heavy cables going to for shorts to chassis/deck'? As in, from the cables?

Sorry, I obviously have no idea what I'm doing. Thanks for the help Badcaps!

[firefighterfox]

Re: LG 50PA5500 plasma won't turn on

Hello Forum,
I would like some information / opinions on my Lg 50PA5500 plasma flat screen tv.
I purchased the tv as a dead set. It came with no base or wall mount. I was able to get the set working by replacing the Y-sus and upper buffer boards.
I have read several comments about this model having ribbon failure problems. I have no indication that there is a problem in this area.
So here is my thoughts for what they are worth,
1st: if it's not broke, DON'T FIX IT
2nd: attempt to repair the issue that causes the ribbon failure (need a good picture identifying that if possible)
One last comment / question. Is there any information out there as to whether the ribbon failure could be provoked by using wall mount rather than a stand?
thanks for any input / thoughts.
firefighterfox

[yompi]

Re: LG 50PA5500 plasma won't turn on

OP were you ever able to get this resolved?

[firefighterfox]

Re: LG 50PA5500 plasma won't turn on

Well I'm finally back on the LG TV trail. It's been sitting under cover on my work bench. I think it's time to "use it or loose it".
Starting from scratch because I don't remember where I left off. Just checked power supply voltages. 5 volt supply reads 10 volts, VA reads 121 volts, and VS reads 450 volts. Obviously way too high.
I'll try another meter to be sure. Also the voltage remains the same with or without the y sustain ribbon plugged in.
Also, do I need an antenna or video source plugged into the tv while checking for audio and or screen illumination?
Thanks for any help.

[dick_barton]

Re: LG 50PA5500 plasma won't turn on

Those voltages appear to be double. Has the meter been set to AC and not DC?