LG 42PT350R Clicking Array

[chaplu]

Hi,

I have 3 years old LG 42" PT350 tv. Which recently started making humming noise and eventual failed to turn on. It only clicks and then go back to protection mode then clicks and so on. I checked va vs on power supply they are within specifications which is va 55v and vs 203v. So power supply seems ok. when i remove the z-sus board from power supply tv turns on but without any picture which is expected.

So removed z-sus and found two 30F124 shorted. Replaced them and reassembled again. Turned it on to find that symptoms changed a bit. It was clicking with more delay now. Then i turned off and removed the y-sus from z-sus board and tried running again. It made humming noise again and back to same clicking with short delay.

Opened z-sus again and to my surprise 30F124 both are shorted again.


Seeking experts support on this.

Thanks

[tom66]

Re: LG 42PT350R Clicking Array

When you replace an IGBT, it's important to also replace the driver IC which goes with it.

[chaplu]

Re: LG 42PT350R Clicking Array

Hello Tom,

Could you help me locate driver IC?

Thanks

[tom66]

Re: LG 42PT350R Clicking Array

Can you post a picture of the bottom of Z-sustain board? The green coloured side.

[chaplu]

Re: LG 42PT350R Clicking Array

Here's back side pic

Thanks

[tom66]

Re: LG 42PT350R Clicking Array

driver ICs are IC7,IC8. (I assume you replaced the two IGBTs with solder marks on them?)
Replace these along with the IGBTs.
Check all resistors around IGBTs too.

[chaplu]

Re: LG 42PT350R Clicking Array

yes solder marks on them. Ok I will do that. Do i just check resistors and call it done if all ok? or need to check anything else as well? I don't really see the ic number on them it is something like x813 and below that it says 73711 etc. What might be the ic number.

Thanks for the help Tom. Much Much appreciated.

[tom66]

Re: LG 42PT350R Clicking Array

More than likely FAN73711, high side IGBT/MOSFET driver.
http://www.fairchildsemi.com/pf/FA/FAN73711.html

If resistors are OK, no need to replace them, but as they cost so little, it could be prudent to replace them regardless.

Also check Y-SUS for shorted IGBTs; if you find any, you will need to repair both boards as a bad Y-SUS can damage Z-SUS and vice versa on these newer panels with "chained ERC".

Forgot to mention check the little zener diode ZD2 near one IGBT - if bad use a 18V to 22V SOD-323 zener.

[chaplu]

Re: LG 42PT350R Clicking Array

Ok, I will do. Do i need to check smd resistors as well? or the big one only. I didn't check y-sus board but will have a look on it as well.

If IGBT on y-sus is ok, should i go ahead and do further testing on y-sus?

Edit:
Just tested IGBT on y-sus and they seems ok.

Checked zd2 and it is bad (shorted) zd1 is ok though. One more thing to mention is RD2004 shows continuity on each pins vice-versa on z-sus board whereas it shows continuity only on two pins on y-sus is that ok?

Thanks once again for your help.

[tom66]

Re: LG 42PT350R Clicking Array

You'd need to check those resistor and zener out of circuit. You can lift one leg of the device and check that way.

One way to see if Y-sus is OK, will set run without Z-sus? i.e. no shutdown. You won't normally get a picture on these, but you should get -Vy/Vsc voltage on output, and slight buzzing, if only briefly from Y-sus.

[chaplu]

Re: LG 42PT350R Clicking Array

set runs fine without z-sus connected with no picture. but y-sus is getting power from z-sus.

So should i assume y-sus is ok?

[tom66]

Re: LG 42PT350R Clicking Array

It probably is if all IGBTs test OK, but unfortunately, no way to be sure.

[chaplu]

Re: LG 42PT350R Clicking Array

Alright, Will report back tomorrow when i will get the parts and done with my testings.

Thanks Tom for attentive help.

[tom66]

Re: LG 42PT350R Clicking Array

No worries, let us know how it goes. In India, do you have that kind of immediate access to parts, like market stores? That is great if so. I would love to have that, nearly everything has to be ordered by mail/internet here.

[chaplu]

Re: LG 42PT350R Clicking Array

Yea we do have market here near by. Can get most of the things here. But unfortunately i wasn't able to source 73711 IC here . Is there any substitute to it. Also is it possible that driver ic are not bad its just the zener diode?

[tom66]

Re: LG 42PT350R Clicking Array

If the zener diode were shorted, it would simply stop it from working, the IGBTs would probably not blow, it just wouldn't light up the plasma panel. You might be able to get the required ICs from other plasma sustain board. I know Samsung use them on some models, common IC. What electronics distributors can you order from - maybe Newark or Farnell?

[chaplu]

Re: LG 42PT350R Clicking Array

Hello Tom,

Sorry was busy with my work, bought another tv for the time being but still i want to fix this tv. I already replaced the driver ic as well as igbt's and one zener, set still clicks if i remove the power cable from z sus and let it stay connected to y sus. it turns on but no picture, i mean red light goes on and off with remove.

What to check now.


Thanks & Appreciate your help!

[chaplu]

Re: LG 42PT350R Clicking Array

Hello Tom,

Sorry was busy with my work, bought another tv for the time being but still i want to fix this tv. I already replaced the driver ic as well as igbt's and one zener, set still clicks if i remove the power cable from z sus and let it stay connected to y sus. it turns on but no picture, i mean red light goes on and off with remove.

What to check now.


Thanks & Appreciate your help!

Bump, forum goes too fast.

[chaplu]

Re: LG 42PT350R Clicking Array

Bump once again, Kindly help out guys if you can. Thank You!

[tom66]

Re: LG 42PT350R Clicking Array

So, are there any shorted IGBTs/FETs on the Z-sustain or Y-sustain board?