LG 50PG20 - Y-SUS/Z-SUS problems after PSU repairedS?

[alecjahn]

After some asking around and ebay snooping/picture dissection of repair kits, I fixed the power supply board on my 50PG20 (I also found a burnt/open fusable resistor that I had to replace, no biggie there though).

For those out there who might find this thread, if fuse F801 is blown, then MOSFETs Q801 and Q802 should be shorted as well and need to be replaced.
This is what I did, then the unit turned-on. Sorta!

Now, I also saw a repair kit for this board that included four capacitors. I figured all mine are just fine, as none of them are obviously blown.

That being said, the TV will not stay on for more than a second after "boot" (when the power light goes solid blue after flashing blue) for more than a second. The screen never lights up.

I disconnected the Y sustain and Z sustain boards, as per recommendation in another post on this forum. The unit will stay on with the Y unplugged - well, sorta.

I decided to check the voltages going to the Y-sustain, and then decided maybe that wasn't going to tell me much (VA and VS didn't show anything, I seem to remember them putting out like 18v? and the 5v line would go from .8v to 1.3/1.4, climbing, until the tv shut off). After that (did I do something stupid?) the TV won't stay on unless both the Y and Z SUS boards are unplugged.
Great! Progress. (-_- ) ( -_-)

I haven't been able to lug a sound source into the room to see if it reacts to that while Y/Z are unplugged, I assume it would/should.

Are there any troubleshooting/common problems I can try/know about when it comes to those sustain boards? Do you think my Z SUS actually kicked the bucket within those few minutes of trying to test voltages to the Y SUS? Should I just buy a new Y (and Z)? Should I eat corn on the cob? Should I drive my Mazda off a parking garage? I figured someone could answer at least a few questions, or give me some insight.



I realize pictures are the trend here, and before someone asks me for them: the TV is in storage right now (where I did all the work today) and I forgot to bring a camera. That being said, there's really nothing I could spot that was obviously toast on either the Y or Z. If someone asks, though, I'll drive across town as soon as I can and get some hi-res shots.

Thanks for your time. This forum/site is a really great place, and I always appreciate when people are willing to take time out of their day to help folks like myself. Cheers!

[alecjahn]

Re: LG 50PG20 - Y-SUS/Z-SUS problems after PSU repairedS?

Sorry for the double post, I don't see an edit button (maybe I'm just not observant today).

I was thinking today, the MOSFETs I ordered are a different package size than the originals. Just a letter difference in the model number. I'm wondering if there's a possibility the PSU isn't supplying enough power to the SUS boards for some reason, instead of the SUS boards actually being faulty. Is this possible?

[dukesaskatoon]

Re: LG 50PG20 - Y-SUS/Z-SUS problems after PSU repairedS?

When the Television has a problem related to;
1) Shutdown caused by Main Board
2) No Picture
This can be checked by the following.
(1) Disconnect the Main Board from all connectors. Apply AC power.
Since P803 is not connected, the set will come on. Short the two pins on the Auto Test
Pattern lands.
If there is a picture of cycling colors, the Y-SUS, Y-Drive, Z-SUS, Power Supply,
Control Boards and Panel are all OK.
Same test for (2) to tell if the No Video is caused by the Main Board.

With the main board removed the power supply should turn on
The two pins are on the control pwb just to the left of ic 171.
with these shorted the control pwb generates test patterns on the display panel.
easy way to trouble shoot all the pwbs minus the main pwb.

the main pwbs are suspect to not turning on the power supply on this model.

[tom66]

Re: LG 50PG20 - Y-SUS/Z-SUS problems after PSU repairedS?

Check the AC Detect pin too.

[alecjahn]

Re: LG 50PG20 - Y-SUS/Z-SUS problems after PSU repairedS?

Alright. So I have to update.

I continued to fail attempting to repair the board. Even bought one of those "kits" that came with some caps and MOSFETs. No luck.

All the while it had been experiencing typical and obvious Y/Z failure (unplug one, stays on... etc).

Finally found a reasonably priced PSU on eBay. It wasn't the exact board model number. Mine was an EAY39190301, and it seems everyone else's 50PG20 has a EAY41360901 (this is what I bought). I took a chance, the price was right, and I dissected the connections of each board and concluded they (the boards,) function the same but have a different layout (components) (but: all pinouts matched, connectors looked to fit, etc).
"Whatever, I'll give it a shot."

Board came in the mail a few days ago, and I installed it this afternoon.

Works perfect.
[see attachment]

This is the corner it sat in for the past couple years.
Pardon the poor picture, but that's the "NO SIGNAL" bar on the screen (which bounces around). It even picked up a local digital channel (no antenna connected) occasionally and the picture looked great.

DISCLAIMER THOUGH!----:
I don't want this to sound like my "obvious" sustain board problems were wrong and are normally wrong. My board replacement worked, I believe, because I was quite sure that was the issue in the first place when I first got the unit. My repairs were not successful on the original power board (heck, I know I broke it even further at some point).
I took a chance, an educated guess, and won. When I first got the TV, right when I got it and before I attempted repairs, it had textbook power supply failure, and kept blowing fuses.
I feel that if the "kits" were available as readily as they are now, I would have snagged a kit and fixed it first-try.


Thanks all,
-Alec

[mattisse]

Re: LG 50PG20 - Y-SUS/Z-SUS problems after PSU repairedS?

Hello I need original numbers of MOSFETs Q801 and Q802 and Q601 and Q602. Thank you