LG MU-42PM12X ysus issue

[freakaftr8]

This has been kinda interesting tv I've had a kicking around the house for the last year and I decided to finally tackle it it uses the P 42 X 2 panel and it had a bad control board the normal red stripes vertical issue. I replaced it with the control board that I found on ebay even though this control board is known for a bad soldering connection underneath the IC I took a shot and used it anyways well the TV work for the first few seconds and then I noticed the screen got all white mal discharge looking and then the Ysus popped

what ended up happening is it managed to blow Q51. It's a 2SK2673 mosfet along with R79. I replaced all the components that shorted but yet I still have Issues. I have replaced that control board with a known good one and still have issues mainly as soon as you powered on you have really bright sparkles definitely mal discharge also the no signal banner on the screen is all white any menus that pop up all white you can't read them. looking at the circuit the MOSFET that blue controls Yramp. has anyone had any experience with this Ysustain board? It's a LG 6871qyh030c

sorry I have typing issues my phone is totally messed up after I did this software update To android jelly bean 4.3

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Btw if I leave it on it will blow Q51 and R79 again.
http://i845.photobucket.com/albums/a...ps3d7c0d2a.jpg

http://i845.photobucket.com/albums/a...ps1bcefca5.jpg

It.seems that yramp is maxed out and not doing anything but the rheostat is OK and no shorted diodes.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Found a 1k Smd Resistor And a 5 Ohm smd both running the yramp pot open. I'll replace both tomorrow and repost.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Replaced the smd resistors that were open and blew R79 again. Can't seem to find any shorted diodes.
IPM module doesn't show any shorts.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Ok found the issue. Believe it or not it was the lower buffer board causing the issue. Even thou there were no signs of a failed buffer IC, there was a surge and a major overload of the VY circuit. Replaced lower buffer board, problem solved.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

okay well I thought I found the issue here's the deal tell me if this is weird or not. Well of course its weird I wouldn't be posting it duh.

my new Lower buffer bored does the same exact thing. with just The upper board connected the screen looks perfect as soon as I Connect the lower buffer bored the screen starts getting all Mel discharge looking and the white no signal starts flickering pink and white almost like in sync with a frequency cycle of some type. I know if I leave the lower bored in and allow it to keep doing this it will blow the y Board again.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Hmmm q101 and q102 are issues on the p42x2 buffer boards huh? I just found this out.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Anything else besides q101 and q102 I should be looking for in a buffer board failure in these pdp42x2 boards? I replaced the shorted mosfets and still have the same issue.

[tom66]

Re: LG MU-42PM12X ysus issue

Do you have a scope to check Yramp waveform? Have you tried with upper buffer removed?

[freakaftr8]

Re: LG MU-42PM12X ysus issue

yes I have A scope. My father in law is borrowing it at the moment. I have tried the TV with just the lower buffer in place and I get the same result. Quite a bit of blue mal discharge and even though I didn't probe voltages at the time because it will immediately destroy the y ramp circuit on that why board if I leave it plugged in for over 10 seconds something is amiss like a dead short. The odd thing about this is the screen is perfectly fine with just the upper buffer installed. and I thought that besides the data signal both upper and lower bored share common voltages.

looks like it's time to ask for my O scope back

[freakaftr8]

Re: LG MU-42PM12X ysus issue

well I went ahead and ordered another Ysus board for this Tv and what I have is a surging pulsing issue with the screen its like the screen tries to cut out every second but then comes back perfect I can't hear anything ticking or pulsating behind the TV but it will do this and Indefinitely now it won't blow anything. I've checked vs and VA and they are not fluctuating. I have a feeling vscan is. I haven't yet checked. the weird thing is is if I start detaching ribbon cables to the Panel via y buffers the picture starts to clear up and it doesn't pulsate as much until I get to about the whole bottom row of the lower buffer disconnected the pictures perfect but as soon as I start connecting more ribbons the picture starts to pulsate. I replaced the YSustain z sustain, control board and upper and lower buffer boards. Vscan is controlled by Ysus. and I don't think it's a power supply issue at least to the best of my knowledge considering that the main voltages are not fluctuating. I created a video I'll post it soon

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Here's the video
http://s845.photobucket.com/user/inf...2a3d8.mp4.html

[freakaftr8]

Re: LG MU-42PM12X ysus issue

does anyone know what the Vscan voltage should be on this panel? I don't understand the label on the panel..

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Vscan is jumping all over the place. The more.load put on that circuit the worse it gets. If I leave only one buffer board in vscan can supply properly.


To me it seems.loke a capacitor issue.

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Still looking into this tv and why the vscan surges. I nnarrowed it down to ysus. Any iideas? It's just vscan doing this. Mosfets seem good and so do caps. TV is fine if I disconnect some y ribbons as its not dragging the current down as much .

[tom66]

Re: LG MU-42PM12X ysus issue

Checked capacitor on Vscan module?

[freakaftr8]

Re: LG MU-42PM12X ysus issue

well I guess I should looked more when I ordered this board off eBay I should have known better its all hacked up somebody's replace both modules or at least had the board one time and they've also changed out some transformers it looks like or maybe took him off the board. It's lovely. hacked up traces that Have been repaired. this looks like fun

[freakaftr8]

Re: LG MU-42PM12X ysus issue

The caps on the vscan module seem ok against my fluke meter. Don't have a real esr checker unfortunately. Does.the module itself produce and sustain the vscan voltage?

[freakaftr8]

Re: LG MU-42PM12X ysus issue

Ok so i noticed that there is a subtle ticking noise coming from or around the vscan module on the ysus. I've encountered shorted diodes in the past On ysus boards but nothing shorted here. I did find a bad smd cap c10 on the data signal input to buffers. Replaced that. With data cable disconnected from buffers the picture although distorted is no longer flickering but ticking still present. I'm stumped. Wave forms on that circuit are dropping out but all other waveforms fall in to normal..