LG 42LG3000 TV Board needs replacing, but which one?

[DejaVu]

Got my boy another TV reasonably cheap knowing it needed a new board, but I'm not sure which one.

I've checked all the capacitors and all are completely flat with no sign of leakage.
I've looked on YouTube at a Professional TV repair companies video and they seem to think that if the TV turns on, then immediately off again, it could either be the PSU Board or the Video Input Board (with HDMI/Scarts etc).

This is the video that I watched -
http://www.youtube.com/watch?v=0y9wxvuKJtc

I've also checked the fuses for continuity and they are both fine (the TV turns on!)

However, when I turn this set on, in warms up as normal (LED flashes 3 times, attempts to power the Backlight and as soon as it does, it flashes and powers off - completely off, not in Standby.

I can turn it back on straight away back into Standby, but when trying to power up, it does the same thing.
This leads me to believe that it is one of the 2 Invertor boards (TV has 2, a Master and Slave) - especially as one makes a 'fizzing' noise as it tries to fire up the backlight.

I'll upload a video shortly (once my phone charges) to show what I mean.

Anyone experienced in TV repair?
I've repaired a few in the past, but the faulty board was obvious.
I know I've got to get one, I just want to make sure I get the right one!

--edit
Here's a video of what the TV is actually doing. Note the LED bottom right, the fizzing noise can just be heard too as it attempts the backlight.
http://www.youtube.com/watch?v=LCWH8EON5j8

[maltloaf]

I've checked all the capacitors and all are completely flat with no sign of leakage.

erm, you can't really check capacitors with a spirit level and a bit of tissue

[-X-]

im no expert like you i fix these as a hobby.
that said i wouldn't assume a cap was ok because there was no sign of leakage i would meter them and prob swop them out to be sure,. psu as you know are the most common issue.
i have a samsung here that has a very similar fault it turned out to be the tconn board, the small board at the top that the lcd ribbon connects to. if you disconn it and see if you get a green led then
what i would suggest if you fix a few here and there register on euras with some made up details this will list the most common faults that you can check,.
http://www.euras.com

[DejaVu]

I'm not assuming the Caps are fine, I'm saying that everything seems OK with them.
I realise these things are the usual cause of failures and have replaced some in the past that where bulging/leaking and repaired the fault.

Just this occassion, there is no sign of anything, all completely clean, zero bulge and the 'Pen marks' on the top are still all intact.

Based on the 'Fault Symptoms' from this page, it looks to be practically the same issue this TV is having -
http://www.coppelltvrepair.com/p/542...-image-problem

Before I got hold of the TV, the original owner said it had sound, but no picture for quite a while. 'Point 2 and 3 are practically explaining the issue I'm having, even down to the loud(ish) buzzing.

Will disconnect the invertors tomorrow and see if 'the short' is gone and if the TV remains on. Didn't want to do this till getting confirmation it wouldn't mess something else up.

Don't you just love the internet. Try fault finding your TV 15 years ago! lol

[-X-]

sorry misread post ignore

[DejaVu]

No probs. Always appreciate members input. Could have been something like that I might have overlooked.

Sent from my GT-I9300 using Tapatalk 4

[AD]

I have an LG that had sound but no pic. Reflowed the T-Con board and it fired back up...

But if you want proper help head on to badcaps.net and jump in their forums. Some really helpful chaps over there!

[-X-]

No probs. Always appreciate members input. Could have been something like that I might have overlooked.

Sent from my GT-I9300 using Tapatalk 4

just to clarify i had replied to your second post but misread it so edited it out, i did suggest you try point 3 in the link you gave only to notice tbat was your next step hence the edit
my first post about the Tconn still stands as it would produce the symptoms you describe, if unplugging the invertor has no effect that would be my next point to check as it has the same symptoms you describe audio but no picture .both are easy to check just by unplugging them.
good luck with it anyway.

[DejaVu]

Ok. It's very late, I was in bed, but this was really bothering me and I had to know. So I did a proper test in the middle of the night!
I didn't realise, but the TV actually doesn't go OFF. It does fire up and the light, after the red flashing goes, stays a faint blue, not able to see with the room lights on, but with the lights out - it's alive. Result.

I removed both Invertor boards and the flash doesn't happen, as expected, but of course, the TV stays on - or at least I'm guessing faint blue is on.
So here is a complete back pedal and much appreciation to -X- for pulling me up on my assumptions.

Still, it could be the invertor boards as the backlight fails to fire up and as far as I can tell, there is no picture, even a dark one behind.
Plugged Laptop in via HDMI, no Dice. But the laptop does recognise the Extended display with Red light - but not with Faint Blue... plot thickens.

Following on from AD's advice, I've registered over on Badcaps and had a poke around there - great forum AD!

According to those guys,
If the Master tells the Slave (dubbed a dumb board) to fire and it doesn't, the symptoms could result in what I'm having here - iffy Slave invertor.
If the Master is screwed, nothing at all happens, not even a flash.

Glad I got up for that, now I'm even more confused! lol

[plug1]

Lda48a service manual .
http://servicemanuals.pro/serviceman...a/details.html

[plug1]

Tbh the boards are as cheep as chips , I would start with a psu kit ,and the inverter boards , maybe disconnect the tcon
and see if the back light comes on first.
These guys are cheep and usually deliver next day http://flattvparts.co.uk/

[-X-]

usually that blue led would be visible the fact its dim makes me think the board is draining some were or not powering up right
if it still done the same after unplugging the inverter and the T-conn i would be looking toward the psu

edit: just to add i also use the link posted by plug to order my parts,

[DejaVu]

Removed the Invertor and TCon boards. Blue light still Dim.

If I disconnect all boards apart from the PSU, should the light glow Blue?

--edit
Nope. Needs the 2 boards. PSU and Main Board so is either of those.

[AD]

Have you seen if you get 12v to your mainboard when you turn your set on?

I take it you have a DMM (digital multi-meter)?

[DejaVu]

I have a Digital Multi-Meter (Sinometer MS8230B).

I'm not gonna lie - I've only ever used it to check continuity with fuses!

How do I go about checking for 12v to the mainboard?
Obviously, the cable that runs from the PSU to the Mainboard, but how do I test which wires which? They are all grey!

--edit
Connector on PSU that goes to the Mainboard.
https://www.dropbox.com/s/wzjvwss9gz...2018.01.18.jpg

I'm guessing from the picture above...
Black (COM) on GND and Red (VΩmA) on 12v with the DMM set to 20v?

--edit 2
Good call AD. Just tested as above on 5v and 12v. 5v reporting correctly. No 12v coming from the PSU!

[plug1]

Try this conect it back up and heat the psu up with a hair dryer ,quite a good going over , then try power the set.

if you contact the site I posted and tell them your not too sure which board
and ask them to send both the psu and the inverter boards ,the might charge you a small re stock ,to send the other back , or they might even just refund you .
worth asking .

[AD]

Now that you have checked the 12v when you power the set on does the back light come on? Check through the vents to see if you see any light or anything?

Could be psu but more likely the main board.
Now check the on/off pin. ground the black terminal from your DMM to the metal chassy of the tv and put the red probe on the on/off pin, with power plugged in and turn the set on. Do you get a different reading from the off state?

[AD]

I see Tom66 has replied to your post on Badcaps with the same suggestion. Tom66 knows his shit

[plug1]

Have you seen if you get 12v to your mainboard when you turn your set on?

I take it you have a DMM (digital multi-meter)?

im not sure have measured correctly , totally unplug the psu from all other boards .
put the black lead to one of the screws holing the psu board , set the meter to 30v dc or abouts
Look the service doc I posted and test the pins .
But tbh it doesn't really tell you if the psu is at fault , even if all voltages are present .
its cheeper and easier to swap out the boards .
if you power the tv on with the lights out ,back off , you will notice if the cfl backlight , begins to start .

Good luck.

[ozy]

first check the fuses on both master and slave inverter (white smd near socket) not likely to be your problem but check them anyway.

check for dry joints on psu and check all electrolytic caps, just because they look ok does not mean they are, check them with esr meter if you have one.

you have a 5v standby voltage from psu to ssb the ssb then applies 3v to ps_on pin, telling the psu to switch on the other voltages(5v,12v,16vand 24v)

if you want to test psu on the bench you will need to connect a 100 ohm resistor between 5v-standby and power on pin.