LG ws2243s monitor repair

[dark_samus]

Hello EEVblog forum, I've had a monitor that has been on the shelf for a few years as it isn't very reliable, I recently got it back out and, once I got it to turn on, noticed how good it looks, I'd really like to use it, but again it's very unreliable. The problem is as follow; the monitor 99% of the time, when powered up, will immediately go into standby mode (no power on the backlights and the LED on the front flashing on and off) doesn't matter if I've had the monitor on for awhile I've tried the couple of computers I've had through the years and with about 3 different graphics cards, if you wait long enough (it varies... sometimes 15 minutes sometimes 3 or 4 hours or even longer sometimes) the monitor will all of the sudden just pop on, if you don't want to wait smacking the back of the monitor most of the time will make it come on (you have to use considerable force and sometimes it takes 10-15 smacks to get it on). Interestingly if you take the monitor apart (just take the plastic shells off) unplug the logic board (where the video in signal comes from) from the actual panel (leaving the backlights plugged in) the backlights immediately come on and act as though the monitor has come on, plugging the panel back in makes the panel come on with the proper picture and then it works fine after that. The service manual for this monitor does contain a schematic of all of the electronics except the ones on the actual panel's circuit board (which I'm very much beginning to suspect as the culprit) except the logic board is all wrong for this model (another model seems to have that logic board actually). The power supply does seem to match up as far as I've bothered to trace it however. If it really is the panel circuit board I'm thinking of making a small circuit with a micro controller that basically goes between the panel and logic board and when the monitor comes on it cuts the power for a certain amount of time and then puts power back as this would mimic the unplug then plug back in that works every time... any help is appreciated

service manual: http://diagramasde.com/diagramas/otros2/W2243S-PF.pdf

[Rasz]

caps

[wasyoungonce]

Yep Capacitors in PSU.  I have LG W2250TQ FLATRON....kept staying in standby...Caps!  Ensure you replace all in the PSU section.  The LGs around that era were notorious for "bad caps" it shows up like a rash on google searches!

[dark_samus]

I forgot to mention, I have replaced all of the caps... it was doing it before and after cap replacement

[wraper]

I'd guess cracked solder joint. Probably in PSU, 1 layer boards are much more subjected to this thing. Or some connector, probably crappily crimped wire in the connector. I'd start poking PCBs in powered monitor with some insulated tool and see if this have is some effect.

[dark_samus]

I'd guess cracked solder joint. Probably in PSU, 1 layer boards are much more subjected to this thing. Or some connector, probably crappily crimped wire in the connector. I'd start poking PCBs in powered monitor with some insulated tool and see if this have is some effect.

if that's the case, then why would it come on without touching it if I wait long enough and why would it reliably come on after disconnecting and reconnecting the panel from the board?

[wasyoungonce]

All the caps...even the ones near the switchmode controller?

I at first didn't do these on mine...the fault still continued.  I looked at some google hits on caps for this board..they didn't include the caps near the switchmode controller!

Also look for a service manual for the monitor...I found one for mine W2252TQ...but it didn't have any schematics of the PSU except for a block diagram.  Guess they didn't think it important enough to work out.

[dark_samus]

I replaced all of the electrolytic caps on the board except the giant one... unless it's not one of those? Also do you think it might be worth replacing the big one?

[wasyoungonce]

No that's just the tank capacitor supply they rarely fail.

[dark_samus]

No that's just the tank capacitor supply they rarely fail.

so then what else could it be?

[wasyoungonce]

Ggoole for a service manual.  I found one for my W2252TQ...I can send you a copy but there will be differences.  Best you find the one for your monitor.

edit:

sorry you have one....and it doesn't show what you need.  Are all the power outs from the PSU ok, 22V and 5V.

Looking at the PSU...I previously meant C105 near U101.  Sometimes this is not changed..has this been done?  Also C103?

[dark_samus]

I know 5v is.... I can't remember if I checked the 22v rail, though I'm pretty sure I did... I can retest.... also when I test should the monitor be doing what I'm trying to fix or should it be fully powered on? ( I'm guessing doing what I'm trying to fix), also thank you for the help so far

[wasyoungonce]

Should be powered on.

Also check IC601 APE8839MP it converts +5V to 3.3V and 1.8V out (pins 1 & 3 respectively).  The troubleshooting guide tree on this is quite helpful.

[dark_samus]

not seeing ic601 anywhere in the diagrams... searched the whole pdf and didn't find it...

EDIT: only thing labeled IC on the psu board is IC801 which is just some 4 pin IC otherwise nothing

so after lots of examining it seems that that service manual has zero to do with my monitor, I mostly was looking at the AC side when I was tracing parts out and I wasn't looking at numbers, none of the numbers match and a lot of the values are just slightly off.... like the big capacitor is 150uF instead of the 100uF in the schematic some things are missing or the number for them is (like c601 or whatever) ~400 off... *sigh* looks like it's for a different monitor than the one I have

[Rasz]

its the caps, either you missed one, used shitty ones, or there is a sick smd cap somewhere on the board
connect oscilloscope and grab the moment you turn it on, you will most likely see voltage sag for a <second, probably 5v because thats what the panel uses

[dark_samus]

Any way I can do that without a scope?

[wasyoungonce]

IC 601 is on the main board, not the PSU.  The PSU basically makes +5V & 22V the main board converts this +5V in this IC (APE8839MP) an 8 Pin DIl package.  It's (the 3.3V/1.8V IC) on the same board as the main processor the board has DVI input etc.

If your PSU board is different can you take a pic of it and or identify a model number of the PSU?  Still betting its a cap in the PWM area of the PSU.

[Shock]

Plan a methodology that simplifies testing (without the PC if possible), preheating and/or cooling down the boards, if you cannot isolate it to a certain board or component and CCFLs have some decent hours on them, inspect to see if they are burnt/worn (same symptom).

[dark_samus]

I mentioned in the OP that the logic board part of the schematic matched nothing on my logic board but matched another models logic board... I can test without a PC as it should always fire up and display a "check signal cable" message on the screen but even when it's supposed to do that it will go directly to standby mode, I have inspected the CCFLs and they're just fine, no burning or wearing on them, and with the panel disconnected they reliably come on

These are too big for the attachments so https://www.mediafire.com/view/efgm3pc0mnw5r8k/IMG_20150811_112248.jpg
http://www.mediafire.com/view/ef1zvzgntk73k4x/IMG_20150811_112349.jpg

[wraper]

I'd guess cracked solder joint. Probably in PSU, 1 layer boards are much more subjected to this thing. Or some connector, probably crappily crimped wire in the connector. I'd start poking PCBs in powered monitor with some insulated tool and see if this have is some effect.

if that's the case, then why would it come on without touching it if I wait long enough and why would it reliably come on after disconnecting and reconnecting the panel from the board?

PCB heats up, thermal expansion, contact appears.

if you don't want to wait smacking the back of the monitor most of the time will make it come on (you have to use considerable force and sometimes it takes 10-15 smacks to get it on)

I really doubt that with just faulty capacitors or other parts, beating the monitor would have any effect.

[dark_samus]

I should also mention that unplugging the panel from the logic board and then plugging it back in will let it come back on from just pushing the power button like it should normally, this only lasts a few hours or less though... The whole thing is really strange

[divelectservices]

Which connector are you removing and replacing to make it work?

[dark_samus]

The one between the panel (lcd) and logic board (video input board) it only works if it's powered up and doing the undesired behaviour if it's off messing with that does nothing but while its in standby mode pop the connector off, wait for the backlights to do their thing, pop the connector on and screen comes on and displays just fine and turns on and off normally for a little while then goes back to the way it was before

EDIT: old Murphy is back at it again.... Got some footage of the problem but it's basically corrupt and way to large to upload (my phone was trying to record 4K >.<) went to get more and the monitor has been working fine for hours now.... Not exactly a bad thing but still odd

[wasyoungonce]

The PSU is known as E59670...looking for schematic now.  Also known for LG as ILPI-145 REV A

Annnd i think this is the schematic (opens in a pdf)
https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CCQQFjABahUKEwioipPttKLHAhVh56YKHav-Ca8&url=http%3A%2F%2Flinfotech.co.uk%2Fschematics%2FLG%2FLG%2520W2234S.pdf&ei=C6TKVejYL-HOmwWr_af4Cg&usg=AFQjCNHj_bhbrcwca8hLbufhTj6SF5oMcw&sig2=wu3yjac0L5uaT-YqI46oaQ&bvm=bv.99804247,d.dGY

There appears to be an issue with the CCFL inverter...a capacitor that goes bad...see here.
http://www.badcaps.net/forum/printthread.php?t=10119&pp=20&page=4

[Rasz]

you didnt replace caps on the scaler board, did you?

[dark_samus]

you didnt replace caps on the scaler board, did you?

The scaler board meaning the board with VGA? If yes then you're right I didn't replace those

I'm really really sure it isn't the inverter circuit btw as mentioned the CCFLs reliably come on with the LCD disconnected

[Rasz]

you didnt replace caps on the scaler board, did you?

The scaler board meaning the board with VGA? If yes then you're right I didn't replace those

then you know what to do next

[Shock]

I recommend you do some hot and cold testing on the power PCB and the logic/video PCB and only test it isolated from the computer.

Test in a logical manner and fully disconnect power between each test. If it's showing the fault get it warm with a hot air gun or hairdryer etc (no more than 60C/140F). Then get it to fault again, so a fan, freeze spray, canned air, dab alcohol and blow on individual components directly or with a straw (causes evaporative cooling).

It's handy to ascertain the time before the symptom reoccurs. When you cool components allow the circuit time to naturally cool and residual charges to drain, several minutes between powering, until you can get it work/fail on demand.

An ESR meter works best for caps, it's a 50/50 chance of the ones you haven't replaced causing the issue, but I'd stick to the isolation part (hot/cold testing) if you cannot quickly test components accurately.

[dark_samus]

I recommend you do some hot and cold testing on the power PCB and the logic/video PCB and only test it isolated from the computer.

Test in a logical manner and fully disconnect power between each test. If it's showing the fault get it warm with a hot air gun or hairdryer etc (no more than 60C/140F). Then get it to fault again, so a fan, freeze spray, canned air, dab alcohol and blow on individual components directly or with a straw (causes evaporative cooling).

It's handy to ascertain the time before the symptom reoccurs. When you cool components allow the circuit time to naturally cool and residual charges to drain, several minutes between powering, until you can get it work/fail on demand.

An ESR meter works best for caps, it's a 50/50 chance of the ones you haven't replaced causing the issue, but I'd stick to the isolation part (hot/cold testing) if you cannot quickly test components accurately.

Doesn't really matter if I leave it for 3 days or 5 minutes between powerups it will immediately go into standby.... Also doesn't matter how long it's on (after I get it to properly come on) I can turn it off and when I turn it back on it starts again.... Heat doesn't seem to be an issue and its not like it's random it's on EVERY SINGLE power up that it does it...

EDIT: now the monitor won't do the undesired behavior *facepalm* it'll probably be back to its usual stuff soon