LG Plasma 50PC1DR- Y-SUS Issues

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

i didnt swap any ipm on the zsus. it seems the ysus is more prone to failure ?

do you have a clue can be causing that w9nk70z chip to blow ? they take away a resistor (smd) and the 2 bigger smd resistor. i've replaced the chip 2 times now from chips from a spare z-sus, but it blows everytime. batch code isnt the same but it seems that it's the good chip..

it seems to be the 'ramp_up' circuit, and it blows right away on tv startup. the ramp_up pot is not working since the circuit is broken, and i have no control on it

i wish i could understand why is that thing blowing !!

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Which chip is it that blows? Didn't you have the same problem with TV #2, and it was a bad IPM that killed it?

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

its the w9nk70z that blows, with the 2 10 ohms smd resistors and another resistor. see picture attached !

well had many issues.. but all were somehow different

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Here's where a scope would be handy. I'll bet SUS_OUT is doing something it shouldn't. If SUS_OUT remains high for too long, then the 5 ohm resistance will be shorted to ground by that FET. High current ~40A will flow, frying the FET and resistors. Perhaps somehow the gate drive to the FET is faulty or perhaps the IPM is at fault.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

um. the gate drive.. that's the circuit around the fet itself ?

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Yes. I think it gives it a ramp signal on the gate, which generates the RAMP_UP drive. If it's stuck high, maybe the FET is stuck ON, leading to failure.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

so im probably missing something bad around that area on the board..

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Possibly. You could do a comparative volt meter with your working boards. Check the gate pin of the mosfet.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

im having issues with some ipm i fighted with earlier. its got missing traces and its nearly impossible to do a proper job with the heatsink installed.

if im using thermal paste and cyanoacrylate on the black plastic tabs, would you think the ipm heatsink will stay there without falling down ?

crazy glue is pretty strong so on both sides.. maybe even adding a tab of sillicone on 4 sides after it's dried up, on the 4 sides of the heatsink between the heatsink and the pcb... sounds weirdo, or could be ok ?

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I really have no idea, as I have never replaced an IPM, and plan to avoid it! If you are using any kind of glue, make sure it has good thermal conductivity. Most are very good insulators, making the heatsink less effective... and those IPMs run very hot.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I've used m4 10mm screws from the top of the ipm (just drilled the plastic holes in ipm + heatsink a bit bigger) and screwed from the top. perfect !

just one thing im wondering, those ipm's run quite hot do they ? even to hot to touch.. should i add some (maybe 80mm) fans to those units ? is really the heat the cause of their failure ?

i was thinking of adding at least 1 fan on each side of the plasma on the ER IPM.. the one that runs hotter

still one y-sus to fix on that 3-plasma project found a few burnt resistors near the fet that always shorts.. maybe it was just those smd resistors that ive missed that got that thing shorted every time.

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I think it's a combination of heat and early IPM design that leads to their failure. But I'm not at all sure. Adding a fan might help.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Good morning. I was wondering, while looking for buffer chips, if there was any x-references for the lg buffer chips on 50pc3d buffer boards..

On the lg boards, they are SN755866. Looking around, i thought, i could use a cheap buffer board with similar chips and use the ic's, would be cheaper.

Here is what i've found, a vizio buffer for 9$ with many ic's. the chips look similar, but are the 2 ic models compatible ?

I wasnt able to find exactly what it was, but i can see FC or something on the chips.

Here is the board itself from the vizio :

http://www.ebay.com/itm/271069140173

And here is a better hq picture of it..

http://i.ebayimg.com/t/LG-6871QDH117A-YDRVTP-/00/s/MTA2NlgxNjAw/$T2eC16dHJGkE9no8iPiUBQQ2jRNbmg~~60_57.JPG

It seems to be FC or FE.. Anyone has a clue what they are and if it's the same ic by a different mfg ?

Thanks in advance !!

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

It's FE, I don't know if they are compatible but if the boards share the same part # they probably are.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Okay. Grrrrr...

I have another issue with one ive fixed here, where it does horizontal lines across the display. ive swapped z-sus and it didn't change anything, voltages are all set according to panel, ive messed with vsetup, vsetdown and that other pot on the ysus but i can't get rid of those lines.

What can cause such lines and how can i fix this ? is it caused by the panel aging, is this something i could fix using the service menu ?

ive tried messing with vs and va as well, it didn't change anything.

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Buffers, possibly. Care to share a picture?

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

okay, after a few minutes the screen became all purpleish. here is what it looks like

http://www.youtube.com/watch?v=zqggVr__vVI

those are the lines..

then it started going purple

http://www.fusioninformatique.com/temp/purple.JPG

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

its not the buffers, i just swapped them from the good working set.. will continue swapping boards

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

not the ysus either...

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

here is what i get with 1 top buffer connected on a hdmi input with no signal (i know half of the screen is off, bottom buffer is missing)

it's blue lines that moves a little bit.. pixels move around

so far i've swapped the ysus, zsus, 2 buffer boards, power supply and it's still doing it

at the bottom of the tv, there's some other buffers there ?