LG 50PZ550 plasma help with diagnostics

[jimbofz]

Hi everyone ,ive had limited success in the past lg plasmas usually with igbt,s lasting a few minutes before blowing on y sus boards ,
however this one had s/c on Z SUS BOARD q114,q115 igbt ,and q104 all s/c
i removed both y sus and z sus
and soldered up the coils that cause problems i also checked the buffer boards i,cs for s/c(often the top i/c)

So rather than repair the board this time
i bought a replacement z sus board
and before fitting i soldered up the coils and checked for dry joints .

My big mistake was i DIDNT check with my meter the igbts and mosfets on the replacement board
i was greeted with same symptom at switch on one click then off . and the same items were s/c.
so here are my questions can you run the psu into a load such as a100w bulb to ensure the psu is not over volting?
can you run the tv without the z sus ,to test the vs 201v?
is it possible that the y sus board can damage components on the z sus?
i suppose the replacement may have been faulty ,(knowing my luck)
im about to order the parts to repair original z sus ,but dont want it to fail at switch on .
any advice from experienced plasma repairers would be very welcome
pics will follow

[jimbofz]

Re: LG 50PZ550 plasma help with diagnostics

here are some pics
on the side view of the z sus ,the front heatsink its the 3 mosfets /igbts ,on the left hand side that fail at switch on

[jimbofz]

Re: LG 50PZ550 plasma help with diagnostics

61 views but no comments?

[zens electronics]

Re: LG 50PZ550 plasma help with diagnostics

Hi , yes Y-SUS can damage Z-SUS , as well as a faulty display .

I have used a 100W bulb on VS supply line from PSU as a load .

To be honest whenever i repair a plasma TV with a sustain board issue , i use a variac to gradually increase the AC supply , as it can save damaging boards if there's an additional issue .

Did you also reflow the large coils on Y-SUS ?

[jimbofz]

Re: LG 50PZ550 plasma help with diagnostics

yes thanks i resoldered the coils ,
if the fault is the y sus ,
are there any checks i can do other than testing for s/c (all the fets/igbt s mearure ok)
if the fault is the panel ,
is there a way of testing ,maybe unplug the buffer boards one at a time?

[zen]

Re: LG 50PZ550 plasma help with diagnostics

I wouldn't run set without Z sustain board , as you might cause additional problems .

Potentially i would assume that there could be one of 3 possibilities .

Firstly , you may have bought a faulty Z board .

Secondly , Y board might have taken it out , although , not sure how you would prove that without replacement , if semiconductors reading good .

Last but not least , potentially the display panel could be taking it out .

I would assume buffers are good , if you have carried out the pin test on chips for short or low readings .

May also be worth pulling out the power supply & attending to any poor joints .

[jimbofz]

Re: LG 50PZ550 plasma help with diagnostics

thanks for reply
ive soldered up and checked psu caps with esr meter
i will run psu into 100w bulb ,if i can find one,and measure o/p volts
i will try to get my hands on a variac as you sugested

[jimbofz]

Re: LG 50PZ550 plasma help with diagnostics

psu runs happily into 100w bulb,all o/p volts correct ,
so if the fault is caused by the panel is there any way of confirming this ?
im trying to get hold of a variac.
i was hoping someone may also have had the problem of y sus taking out z sus,i
and could help futher thanks
it seems odd that same 3 components fail?

[zen]

Re: LG 50PZ550 plasma help with diagnostics

No way that i know of when display develops internal issues , apart from risking more boards .

Chance are , if you cannot find any shorts on y-sustain board & power supply is good , then root cause will most likely be display .

[R_J]

Re: LG 50PZ550 plasma help with diagnostics

You can also unplug the buffer boards from the Ysus board (leaving the buffers connected to the panel) and see if the tv comes on and the Vs voltage stays up. If it does then only connect the upper buffer board back to the ysus (powered off of course) and try again, if it shuts down, remove the upper buffer and only connect the lower buffer. If the fault is with one of the buffer boards, the good buffer should show half a screen (either upper or lower half)

[dannythefixer]

Re: LG 50PZ550 plasma help with diagnostics

Sorry if this is the wrong place to post this (just joined), but can anyone point me to a list of the error codes indicated by the flash pattern of the green LED on the logic board for this TV? (LG 50PZ550)

[tvtimmy]

Re: LG 50PZ550 plasma help with diagnostics

Describe your tvs problem.

[dannythefixer]

Re: LG 50PZ550 plasma help with diagnostics

Describe your tvs problem.

Thanks for the reply! The problem my TV has is that sometimes when I press the "power" button on the remote or the power button on the TV itself (which is a capsense button), I hear a click but the screen never turns on AND the Red "standby" light on the front never turns off. I do see the screen turn a little "milky" and I see a faint ghost image of whatever was there before it went to standby, but the screen doesn't light up. When it gets in this mode, pressing the power button again does nothing (no click and the screen stays "milky"), so the only way to get it un-frozen is to unplug/replug it. This happens in about 1 of every 5 times that I press the power button. In the other 4 out of 5 attempts, when I press the power button it works normally ... the Standby LED immediately turns off and then a few seconds later the screen lights up.

Note that I had originally asked what the blink code for the logic board means, but I have since realized that the blink code is actually THE SAME, when it works and when it fails. Even though the front red LED always follows the problem (LED doesn't turn off in the failure mode), the green LED pattern on the logic board is always the same after the power button is pressed, long-short-long-short.

After reading some threads, I checked for bulging caps but nothing obvious. I checked the solder joints on the large coils on the Z-sus board, and they looked fine. I made a very half-hearted attempt at reflowing the big chip on the main board by blasting the heat sink with a heat gun for ~10 seconds, and after that it SEEMED that the failure occurred less frequently ... it went from almost always failing to failing maybe 50% of the time. Once I realized this, I heated the heat sink for ~30 seconds and it seemed to be closer to 75% success. Tried again for ~60 seconds (most I could stand), and now it's at ~80% success. So I'm pretty sure that my poor attempts at re-flow are helping, but it could just be random.

Advice? at this point I'm ready to trash it if I can't get it to work reliably.

Thanks!

[tvtimmy]

Re: LG 50PZ550 plasma help with diagnostics

I'm pretty sure it's a mainboard problem.

[diif]

Re: LG 50PZ550 plasma help with diagnostics

A decent reflow should take around three and a half minutes to reach peak temperature.
Remove the heatsink and try again with some flux. Ideally the whole board should be around 100c before heating the processor to avoid thermal shock. Blasting just the processor whilst the rest of the board is cold is not a good idea.

[dannythefixer]

Re: LG 50PZ550 plasma help with diagnostics

A decent reflow should take around three and a half minutes to reach peak temperature.
Remove the heatsink and try again with some flux. Ideally the whole board should be around 100c before heating the processor to avoid thermal shock. Blasting just the processor whilst the rest of the board is cold is not a good idea.

Hi, thanks much for the reply! Thanks for advice on pre-heating the whole board.

3.5 minutes? sounds like a long time but I have little to lose since I'm ready to toss this TV if I kill it. To be clear, I don't have actual SMD solder equipment ... I am using a heat gun designed for stripping paint, etc. I wonder if its way hotter than proper SMD rework equipment? Looks like my heat gun offers 750 degrees F and 1100 degrees F (400/600 C)

[diif]

Re: LG 50PZ550 plasma help with diagnostics

Solder melts at 218c so the lower setting should be fine, a cheap TM-902C would give you an idea of the temperature, use flux, cheap Amtech 599 is fake but will be fine.
It's worth spending the extra $ and time I think.

[dannythefixer]

Re: LG 50PZ550 plasma help with diagnostics

OK thanks. I guess I will invest the $30 USD for the temp probe plus the recommended flux (I have an ancient tube from Radio Shack that predates the invention of SMD I think), and that temp probe looks like it could come in handy in the future. Thanks also to tvtimmy for your reply. I will let you all know how it goes once I have the equipment. Looks like that temp probe has a long lead time right now from Amazon.

[diif]

Re: LG 50PZ550 plasma help with diagnostics

Ebay should be cheaper, no penis rocket to fund. I paid less than £10 for mine.

[dannythefixer]

Re: LG 50PZ550 plasma help with diagnostics

My flux and thermometer should arrive soon. What temperature should I try to maintain during the 3.5 minutes of reflow? Obviously it should be above 218 C but how much above? Wikipedia mentions "20-40 degrees C above liquidius". Perhaps I should try to maintain ~250 C? https://en.wikipedia.org/wiki/Reflow_soldering