LG 42PX5D-EB dead

[bbjunkie]

Got this heavy beast for nothing, basically was asked to take it away for scrap.

Got it into the workshop this afternoon and eventually got the back off after plugging it in and seeing that it was totally dead.

Voltmeter out, I started by checking for 240VAC at the input to the PSU board, I'm seeing 0.6VAC wow.. surely not.. surely this repair can't be that simple?

240VAC at the end of the line cord, this only leaves the noise filter where the line cord plugs in.

I have checked resistance between input and output of the filter and am seeing under 1 ohm through on each lead. Across the input terminals a resistance of over 1Mohm (megohm) in one direction, other direction starts at 0.8Mohm and increases to infinity

I am tempted to feed 240vac direct to the PSU input on the board, bypassing the line filter for testing purposes.



I have of course got a 50" plasma in the back of the car that I also collected yesterday (for parts) I may be able to salvage a line filter from it, but it's too late to start messing with it now, that will have to wait til tomorrow. (it's dark now)


Cheers

Jim

[bbjunkie]

Re: LG 42PX5D-EB dead

Pics of course!

[multimeter]

Re: LG 42PX5D-EB dead

just take the line filter out and jumper it,it just means you might get a few discrete wavy lines scrolling across the screen cos of the lack of filtering

[tom66]

Re: LG 42PX5D-EB dead

Wow, Chemicons on the power supply. That's quality, for LG.

I might have a line filter from a computer power supply somewhere. Not sure if it will cope with the 500W or so drawn by a 42" plasma.

eta. The TV should work without the line filter but it will knock out any AM/FM transmissions in the nearby area! Don't run it for long without the filter.

[bbjunkie]

Re: LG 42PX5D-EB dead

Ok, got 240v connected to PSU line in. Now I have stby light and when I press the power on button the set clicks, the stby light goes from red to amber then changes to green. There is a hiss like white noise, the level is affected by pressing the volume buttons, but never gets any louder than a low but audible level.

There are LEDs lit on the main signal board, however not all are lit. LED203 and LED204 are out, however LED203 flashes twice just after switch on.
LED204 flashes once, but only after the set has been off for a short time, if it is just restarted off/on again LED204 doesn't light at all.

I have checked the PSU voltages and have measured:

VA 60VDC
VS 186.8VDC
VCC 5.3VDC
19V 19.16VDC
6V 5.96VDC
3.4 3.46VDC
12V 12.01VDC
AC-ON 4.43VDC
RL-ON 4.41VDC
STBY-5V 4.85VDC
VS_ON 4.35VDC
5V_MONI 5.15VDC

Any ideas where next? This is my first plasma.

Photo quality is rubbish, I have increased the amount of light, but still can't manage to get good pics. I can provide closeups of any board on request.

Jim

[bbjunkie]

Re: LG 42PX5D-EB dead

FS2 a T4AH fuse on the board to the left side of the set that runs vertically (x-sus buffer board is that what it's called?) <edit> LG manual refers to it as Y/B-D. <endedit> is open circuit. I will source one tomorrow and try again.

Should I do any tests before powering up with new fuse?

[tom66]

Re: LG 42PX5D-EB dead

FS2 a 4A fuse on the board to the left side of the set that runs vertically (x-sus buffer board is that what it's called?) is open circuit. I will source one tomorrow and try again.

Should I do any tests before powering up with new fuse?

LG Plasmas tend to blow the sustain fuses occasionally. Sometimes the hybrid is shorted, which is expensive, other times it just blows from thermal stress. With the TV unplugged, test resistance between either end of fuse, and ground (screw hole, frame etc.)

Careful of the sustain voltages. The capacitance on these boards in total is more than 4,500uF at 200V which is easily lethal. You will note the resistors at the top of the power supply board, near the big caps. These perform a controlled discharge of the capacitors when the TV shuts down.

I have that very same Z-sustain I think, so if you are interested, let me know - I'm considering stripping out my current plasma project (LG 42PC1D) for parts, as it's driving me up the wall.

[bbjunkie]

Re: LG 42PX5D-EB dead

LG Plasmas tend to blow the sustain fuses occasionally. Sometimes the hybrid is shorted, which is expensive, other times it just blows from thermal stress. With the TV unplugged, test resistance between either end of fuse, and ground (screw hole, frame etc.)

Checked for short, no sign of one (30K ohms +) I found a fuse in my parts box, only difference was it was a glass one.

Fitted it, powered up and I thought things were going well until there was this almighty bang and flash from the fuse!

[tom66]

Re: LG 42PX5D-EB dead

Checked for short, no sign of one (30K ohms +) I found a fuse in my parts box, only difference was it was a glass one.

Fitted it, powered up and I thought things were going well until there was this almighty bang and flash from the fuse!

So the sustain is shot. This can happen, you will either need to replace one or both IPMs or the entire sustain board.

[bbjunkie]

Re: LG 42PX5D-EB dead

I am considering replacing the IPM (see eBay 180686316348 ) on the sustain board.

Is this item a through hole device? After a short chat with tom66 I have learned they are difficult to remove - i'm unsure if I should go this route or not. Depends on just how difficult I guess

<edit> I have since learned this is the Y-Sus board

[PlainBill]

Re: LG 42PX5D-EB dead

I am considering replacing the IPM (see eBay 180686316348 ) on the sustain board.

Is this item a through hole device? After a short chat with tom66 I have learned they are difficult to remove - i'm unsure if I should go this route or not. Depends on just how difficult I guess

<edit> I have since learned this is the Y-Sus board

What are your soldering skills? I've removed one successfully - and ruined a board attempting to remove another. The best technique is to use a thin screwdriver to break the mounting tabs that secure the IPM to the heat sink, cut the pins on the IPM, then extract the pins one by one. If you have a solder pot or equivalent method of heating all pins at the same time it would be very easy.

PlainBill

[bbjunkie]

Re: LG 42PX5D-EB dead

I'd rate my soldering skills as slightly above average.

I have a lot of experience soldering SMD stuff, bigger stuff maybe not so much up til the last few weeks when i've started on the TV's. Today I was successful removing a heatsink with a pair of diodes screwed to it (10 solder points in total)

I guess it depends on the quality of the PCB - some of them you just need to look at the wrong way and the tracks are peeling!

I'll remove the old one first, if I can get it off without damaging the board i'll order a replacement otherwise i'll order a complete board.

The only thing playing on my mind is do I need to replace the buffer board too? I can get a used ysus and buffer board for 59 plus post whereas the new IPM will cost me 25 including post

I watched a youtube video recently posted by GrantspassTVrepairs, Dave ended up calling it a day after throwing over $200 at a repair involving a (vizio) ysus and still being no further on with it. If I was in that position i'm sure it would spoil the enjoyment of my new found hobby

Jim

[tom66]

Re: LG 42PX5D-EB dead

I'd rate my soldering skills as slightly above average.

I have a lot of experience soldering SMD stuff, bigger stuff maybe not so much up til the last few weeks when i've started on the TV's. Today I was successful removing a heatsink with a pair of diodes screwed to it (10 solder points in total)

I guess it depends on the quality of the PCB - some of them you just need to look at the wrong way and the tracks are peeling!

I'll remove the old one first, if I can get it off without damaging the board i'll order a replacement otherwise i'll order a complete board.

The only thing playing on my mind is do I need to replace the buffer board too? I can get a used ysus and buffer board for 59 plus post whereas the new IPM will cost me 25 including post

I watched a youtube video recently posted by GrantspassTVrepairs, Dave ended up calling it a day after throwing over $200 at a repair involving a (vizio) ysus and still being no further on with it. If I was in that position i'm sure it would spoil the enjoyment of my new found hobby

Jim

Before you remove that IPM, try unplugging both buffers and replacing the fuse. The buffers can short. If it then powers up and the fuse doesn't blow, replace the buffers individually until the fuse blows again. Though I've never seen a shorted buffer blow a fuse I wouldn't class it as impossible.

[bbjunkie]

Re: LG 42PX5D-EB dead

There were two flashes with the bang when the fuse blew. I didnt notice exactly where the first was, but it was definitley on the ysus board somewhere, not as far over as the buffers.

I will try your tip anyway. Nothing to loose!

[bbjunkie]

Re: LG 42PX5D-EB dead

Decided to remove the YSUS board and test the IPM - found the following odd measurements I thought I better run by the experts here!

SUS_OUT -> GND = 0.3 ohms
ER_UP_OUT -> GND = 0.3 ohms
ER_DN_OUT -> GND = 0.3 ohms

I am guessing these shouldn't be shorted to ground like they are?

[tom66]

Re: LG 42PX5D-EB dead

Yep, definitely shorted.

Check this manual for resistance measurements: http://www.scribd.com/doc/7580885/LG...raining-Manual

[bbjunkie]

Re: LG 42PX5D-EB dead

Yep, definitely shorted. ]

Ok, tried desoldering the IPM.. I need a bigger iron!

I can get the loan of a very large iron, think i'll make a copper jig for it so I can heat all pins at once. Saw a Youtube vid demonstrating this once, seems like probably the best way (unless I can get a ysus and buffers complete)

[pecrie]

Re: LG 42PX5D-EB dead

indeed ,a 100 watt iron ,did it for me.One on the sustain and one on the z-board

[pauldow]

Re: LG 42PX5D-EB dead

Today's find at the landfill was one of these with a -UB suffix.
The inside was filled with dust, so I'm figuring an overheat situation. I see that the IPMs are a problem on these, so I got them out of the YSUS and ZSUS boards. The one from ZSUS does smell like something overheated there.

I ran into the the high melt point solder problem. I got it off by prying it up, removing the center screw by grabbing the head with small pliers, and then prying off the plastic frame. I then broke off the brittle pins near the PC board. I added a bit of real solder to each pin, and then I was able to get the pins hot enough to pull them out and suck out the solder from the holes.

That's the good part. Unfortunately, that was on the YSUS which I did second.
On the ZSUS I did first, I was still in unknown territory, and my prying screwdriver smashed FL1, 2, 3, and 4 under the board.

Does anyone know what those are? I got the service manual for this unit, but the schematics don't cover those boards.

Thanks,
Paul

[tw2005]

Re: LG 42PX5D-EB dead

Sounds like fusible links, did you mean topside under the heatsink area?

Is this the type of board?

Have you priced an IPM because there appears to be lots of substitute versions some are quite cheap secondhand.

6871QZH034A, 6871QZH034B, 6871QZH034C, 6871QZH056P,

Some examples.

http://www.ebay.com.au/itm/LG-6871QZ...item3a77f71038

http://www.ebay.com.au/itm/LG-6871QZ...item35c30b4c6c

http://www.ebay.com/itm/6871QZH047B-...item3ccfa4bab6

http://www.ebay.com/itm/LG-6871QZH03...item3a79c55f54