View Full Version : Lg plasma


radio nut
12-04-2016, 02:13 PM
My boss bought a lg plasma TV made in December 2010 model 60pk750-ua. He mounted it and his wife ran it all day.....no problems.
The next day she turned it on and it has sound but no picture on the screen, just dark screen. I usually work on antique electronic items, do I am not sure what to check.
Any known issues with this set?

mstaton
12-04-2016, 05:28 PM
Probably bad y or z sustain board or both. or bad/shorted buffers. Good news, they are cheap on epay. The set will have to opened up and voltages checked. An open fuse on the y or z board usually indicates a bad/shorted board.. Check for vs and va voltages while running. If no voltage is present, remove the power cables on one board at a time and see if the voltage returns indicating a bad board. If no vs or va voltage with both y and z sustain boards unplugged, suspect a power supply.. That should be a good start

radio nut
12-16-2016, 12:28 AM
Ok, info I was given was wrong. The standby light is red, the set will not turn on. I found a 4 amp fuse blown on the main power board. I replaced it and as soon as you plug the tv in it blows that one. Red standby light still on. I do not see any obvious burn marks on the circuit board or obvious bad electrolytic caps........ so....... now what should I do?

Findm-Keepm
12-16-2016, 09:19 AM
Check the rectifiers - both discrete and Bridge (usually fastened to a heat sink...) - for shorts. They'll be near the large (330uf-680uf) 450V cap(s).

Need the 60PK750 training manual? PM me.

radio nut
12-23-2016, 09:55 AM
Rl 103 is shorted. So far I can't find a 5 volt relay to replace it. It also took the thermal resistor next to it out.
My concern now is this, did something take the relay out or is it just bad?

Findm-Keepm
12-23-2016, 10:12 AM
Shorted how? It's an SPDT relay, right? The coil should measure a few ohms, and the NO contacts should be open, and the NC contacts should read as a short.

So what element(s) are shorted? Usually relays fail when the contacts either arc away or arc-weld themselves together.

5V to the relay coil (out of circuit) - do you hear a click?

It is activated in circuit by the RL ON signal from the main board.

Your 4A fuse blowing is from something shorted, but me thinks it's the bridge rectifiers....have you checked them?

radio nut
12-23-2016, 07:28 PM
Lets see, 2 identical relays, the ac connections of one shows resistance. The other reads like I am touching the ohmmeter leads together. Put new 4 amp fuse on circuit board, plugged in only power cord, no other boards, the thermal resistor next to the relay melted and started sparking. That's why I checked the relay

radio nut
12-23-2016, 07:31 PM
How do i check the rectifiers?

radio nut
12-23-2016, 07:34 PM
Antique electronics is my specialty, this is my second flat screen. The first ended up being bad electro's.
So my technical expertise with modern stuff is almost nothing

radio nut
12-23-2016, 07:38 PM
Uhm, 4 pins on one side of each relay, 2 pins on the other side. The relay I feel to be bad shows shorted on all 4 pins. The other relay shows resistance on the 4 pins

mstaton
12-23-2016, 10:53 PM
Have you removed the relay to test it?

Findm-Keepm
12-23-2016, 11:19 PM
Put new 4 amp fuse on circuit board, plugged in only power cord, no other boards, the thermal resistor next to the relay melted and started sparking. That's why I checked the relay

Did you follow the test procedure I posted? Any other action is destructive - you've got to load the supply as they detail in the procedure.

radio nut
01-18-2017, 12:00 PM
Well, it is the bridge rectifiers. ....where do I get another board at?

Findm-Keepm
01-18-2017, 04:56 PM
LG, a donor set, ShopJimmy, or eBay.

LG - gotta go through Encompass
Donor Set - one with a bad screen...
ShopJimmy - 'nuff said..

eBay should be a last resort. 100% failure rate among "tested" boards for me. YMMV, but useless to the serious servicer.