lg du-42px12x vertical lines and sparkles

[cadillacman]

I have this lg here. It powers on, all power supply voltages dead on, has good audio.


the screne comes up fully but its just wide lines basically, that seem to quickly scroll from top to bottom.

A quick check shows that the ysus hybrid heat sink gets pretty hot, the zsus heatsink is a normal warmness.

I will post pics. DOes it sound like a y-sus issue?

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

sorry for the repost that 30 min rule gets me every time.. heres some pics.

[rayrod81]

Re: lg du-42px12x vertical lines and sparkles

Looks like Y-sustain or Y-buffers. It could be the hybrid module. Have you checked the mosfets on the buffers?

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

very quickkly yes but i will spend more time on it tonight and see for sure.

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

Ok.. the outputs ont he ysustain check ok( no shorts) but in circuit, all 4 transistors on the buffer boards cghecked shorted between the center and right leg.

I pulled both boards. Out of circuit, the bottom ones check ok.. but both top ones check shorted.. to narrow it further i lifted the right leg of each transistor on the upper buffer board. q1 is the only one that still checks shorted. its a surface mount fqb46n15

Im going to dig through my junks and see if i have this transistor anywhere else i can rob for testing purposes. I doubt this is my only issue but man ill tell ya, im sure hoping so.

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

success!!!!!!! I replaced that transistor with a b14nk60z i robbed from a old ysustain board.. not sure how close to spec it is, but it works good enough to test with anyways! so happy i got one of these headscratchers figured out!!! WHOOHOO!!!!!!

now as to why it blew.. i dont know. None of the buffer chips run too hot, theyre all slightly warm to the touch, i dont have one or two running hotter than the rest..

can one of you real techs tell me if that transistor is a good enough sub or do i need to come up with something different? (it runs cool to the touch btw)

**bonus points if you know the movie **

[steve2]

Re: lg du-42px12x vertical lines and sparkles

The one you took out is rated for 45A continous drain and the one you put in is for 13.5A continuous drain. I don't know the movie. I saw this model tv at the recycler yesterday. He said it would be $30. I told him I would get back to him. It was raining anyway. I wanted to come home and see what problems are common with this and saw about 4 threads on this tv. I will take a power cord with me and see what it is doing today, if I can get out of the flooded roads.

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

ok so ill get something alot more stout to put in there.. at least i know my issue now..


digikey came up with this- what do you think? its actually rated 5a more then the original..
http://search.digikey.com/scripts/Dk...=568-5951-1-ND

[Th3_uN1Qu3]

Re: lg du-42px12x vertical lines and sparkles

That MOSFET looks like a good substitute in all aspects. Besides current rating, other critical parameters are rdson (higher = will run hotter), and gate charge Qg (higher = the driver stage will have a harder time and the fet may not switch fast enough and get hot).

The one you linked to is better than the original in all three of those parameters.

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

The one you took out is rated for 45A continous drain and the one you put in is for 13.5A continuous drain. I don't know the movie. I saw this model tv at the recycler yesterday. He said it would be $30. I told him I would get back to him. It was raining anyway. I wanted to come home and see what problems are common with this and saw about 4 threads on this tv. I will take a power cord with me and see what it is doing today, if I can get out of the flooded roads.

yeah you guys got some nasssttyyy storms there the last couple days. I hope youre all staying afloat at least

ordered those digikey reccomended transistors along with some other stuff, i will post when this is all done and burn tested to make sure this is the proper fix for this particular issue. unique- thanks for checking specs on those for me.

[steve2]

Re: lg du-42px12x vertical lines and sparkles

I live on Big River and it has been the backyard since 1960. It is 20 something feet below the bank and is normally under 5 feet deep. It came close to coming over the bank and just started going back down last night. In 93 we had 14 inches in the house. The river was 28 feet high. With all the levees and other construction in the floodplains the last few decades, storms like the ones last week cause this lil ol river to flood more than it did and way more often. More rain tonight and tomorrow, but it has dropped 5 feet or so today. So we should be good. I didn't go check the tv, the road to eureka is still flooded.

[cadillacman]

Re: lg du-42px12x vertical lines and sparkles

quick follow up i did finally get those proper transistors. I went ahead and replaced all 4 transistors on the buffer boards to ensure there was no imbalance electrically. (2 on each buffer board) the bonus is now i have 3 good ones to fix other tvs with later on or at least to test with.

Has been running several hours and working perfect.

As to why the original failed, i really have no idea. It was the one at the top, mabye because it ate the most heat? i dunno. Im just glad its fixed.