Need help with faulty PSU board for LG Plasma TV

Thanks snakebite will give it a try. Do the big caps still retain high voltage when unplugged?

assume that they do.
measure before touching.

Since you tried another PSU board that was likely okay even if dirty, and you got the exact same symptoms—then i’m gonna say your problem is NOT on the PSU but on one of the other boards.

You didn’t really troubleshoot this problem and determine that the PSU was bad, you just assumed it was bad, based on stuff you read on the websticle. You obviously don’t have the equipment or skills to troubleshoot it, especially without a schematic. This is too dangerous for a novice.

Yeah, I took a chance that it was the psu after what I read and since the clicking sound came from that board, but as the short could be elsewhere, it could be a problem. TV is at my brothers house, so Monday I will put the original psu back and unplug one at a time the other three boards that are plugged into the psu board to see if that isolates the problem possibly to a board and I can go from there. I'll do my best to avoid a big voltage shock as I like my life at the moment!

I plugged in the original psu board and started unplugging each board to test like you said and the psu works again as long as the large board on the left in the pic is unplugged. I could not see any faulty caps or anything though. Is it worth the risk to try and get a replacement board or can I troubleshoot further now that we know something is going on with the left board? Looks like all the plasma screen lines are plugged into that big board, but how would I test to see if the problem is the board or what is connected to it?

Pic below psu is not in, but you can see the big board on the left. PSU will work if I unplug the top wire to it, or

if I unplug the top wire of the right board where the left board plugs into.

Close up of left board

likely one or more shorted igbt’s.
look at the y buffer chips for burns or holes.thats the 2 green boards left of ysus.
if none found its a good risk to buy a ysus.
or you can get a parts kit and rebuild yours.

I would bet it’s the YSUS, had a 50” LG plasma go out like that. It started with very intermittent pop and momentary screen dim, but eventually progressed to a black screen with sound. Bought a “new” YSUS on Ebay, but got a well used one which still worked for another couple of years of heavy use. Just gotta be very careful not to press on the ribbon cables from the buffer boards to the screen when installing the new YSUS board.

KuoH

Thanks for the help again. Had a look yesterday at the y buffer chips and didn't see anything, but tomorrow I'm over there again and will use my trusty flashlight and a magnifying glass and have a another good look just in case. If I set my DMM to continuity, can I a do a test on the y-buffer chips whilst the board is still connected to the tv or would I have to pull it?

Ours was a little different. Just one pop and then the tv shut down and every time we tried to turn it on it would shut off again.

What model TV is it…might be able to find the cold cathode tube on ebay or something

Maybe he thinks plasma is a form of LCD.
It’s really ashamed manufactures stopped producing plasmas. I love my 2014 Panasonic plasma TV. The general public wants cheap TVs though. And 300 for a 50 inch Vs 600 for a plasma killed them. I think there’s one company that still makes a few

Wow. All these negative waves…

Apologies…didn’t mean to come off as rude or condescending

Googling LG plasma turns off comes up with alot of different fixes, maybe this will help

There’s something to be said about the size and weight of LCDs vs plasmas well. My 50” plasma has been in storage ever since I moved over 2 years ago. The original box it was packed back in won’t even fit in my car and requires 2 people to move as well as unbox and setup the TV. When my “temporary” 42” LCD died, rather than haul the plasma out of storage, it was easier to buy a new 55” slim LCD that fit in the car with the box and set it up singlehandedly.

KuoH

I think the point was about understanding more about the topic before offering advice. What you posted was like someone asking to troubleshoot an LED driver and getting a response like Maglights are notorious for burning out bulbs, did you check for a spare bulb in the tail cap. It was not at all related to the technology or problem, but the responses could’ve been less harsh.

KuoH

No problem…I messed up…apologized for it
Was running empty after a 20+ hr day and was ready for bedtime (skimming thru and not paying attention)

If that is the harshest rebuke for making an ass out of myself I ever get, I will consider myself blessed :slight_smile:

20+ hr days always make me snappy. Easy to understand!

Back in the 90’s I repaired a lot of VGA monitors. Most of them I did not have schematics…….(simply too many different brands). The problems were similar. If no schematic available this is what I would do:

1) Check the internet with model number to see if anyone has posted any info on a similar problem. If one person has a particular problem is means others probably are too. See if anyone is talking about it.

2) Check for bad capacitors. Have to use an ESR (effective series resistance) meter. I never worry about checking capacitance. It’s the ESR that is the issue. Most of the time you can check ESR in circuit without removing the capacitor. Only in situations where the capacitor is in parallel with a low impedance item like an inductor do you get a false reading………but that reading will make it look good. But if you get a bad reading in circuit, then the cap is definitely bad. The electrolytic solution dries out over time and generates a series resistance to the capacitance. If there is a lot of ripple current and filtering going on with that cap, then the added resistance increases the power that will be dissipated by the capacitor and that can cause the cap to get hot and bulge. The ESR problem tends to show up with the higher voltage caps and the bigger value ones. Those are the ones I check first.

3) Bad caps can also cause a power semiconductor like a mosfet, power diode, or other heat-sinked semiconductor associated with that cap’s circuitry to go bad. If after replacing a bad cap and it still doesn’t work, then need to look at the power semiconductors. Mostly look for shorts with DMM.

4) Bad solder joints occur over time………especially the bigger pins and joints. A lot of the time you can see the cracks in the solder but not always. I recently fixed a VHS / combo TV for an older gentleman in my neighborhood and it was a bad solder joint. Never knew exactly which one it was. Could not find any bad caps………so last resort was to just reflow a bunch of solder joints. Problem fixed. (Got lucky)

5) If after spending a lot of time and no schematic or no luck in repairing, I would just call it a wash, give up and move on.

Hope this helps. Some of it has already been talked about, but thought it wouldn’t hurt to mention.

Yup

Model # plus Google/Youtube = your friend (same thing goes for linux as well :wink: )

And I too did almost that exact same troubleshooting method as well…without a schematic it’s hard to troubleshoot unless there is a smoked part that is glaringly evident…

Thanks for the help everyone. So far I have not isolated the problem. Also saw a video of a talented tv repair guy that fixed one board and then tv still did not work. Long story short, he found shorts in all boards and repaired them one by one and finally got it to work. His skills were way above mine.