LG LCD monitor (IPS 277L-BN) repair - Help needed

[Homercleese]

Hello gents,

I hope this doesn't come across as insulting, the fact that I've just signed up only to immediately beg for help. But only one way to find out.

As the subject says, I've got a LG IPS 277L-BN LCD. It's been acting up for the last few months: it started as a whining tone every time I turned it on but that stopped after about 30 seconds. I also noticed that the brightness/contrast would occasionally start to automatically adjust but very poorly, for instance a Windows Explorer window might saturate with white so much that it became a little difficult to distinguish the borders between panes.
Now it's progressed to the stage that the backlight takes several attempts to power on continuously. It'll flick on, then off, on then off, etc, repeating maybe 5 to 10 times before finally catching and running fine for the rest of the on time (thought the white over saturation still happens).

I've opened it up, I'm by no means an electrician but I can spot a swollen cap or a burnt component and solder in a replacement (poorly).

This is the board.

No major power component on here I don't think, there's a PSU brick with it.

I've replaced C130, the 33mu 100v SMD cap but no luck. Still the same behaviour. All the other components look fine. The resistor measures 6.7 ohms (I think it's labelled as 6.4 so that seems fine) and I've checked the voltage at the power connector and it's reading as just under 19V, about 18.85v across a few of the first few components.

I'd read in a couple of posts I found that the external PSU brick often goes but, like I said, it's reading 18.8 approx so that seems ok to me, if obviously not quite 19. I haven't cracked that yet for a look.

Any idea what it might be or what would be advisable to check next?

Thanks for your time.

[montarbo]

See the chip encircled and bit brownish coloring around it!!!
it seems it was heating up. During the Power cycle "on-off" try to locate the two output pins according to attached PDF file. Its a LDO regulator and since its C at end then its dual LDO regulator for 3.3 and 1.2 volts. Measure voltages even for VIN pins- Do the same when its on. Measure even voltage at those pins when saturation issue occurs.

Since there is no schematics then its difficult to give some good advice about where to start.

PS, even if Power supply seems OK, it might yet be the culprit under long lime load!!!! You can crack it open and see for swollen caps or post some pics.

BR

[Koray]

Few years back I repaired an LG monitor with similar issues by cracking the power brick open and replacing the swollen capacitors with high quality low ESR parts. Voltage out was correct but probably it was the filtering that caused the issues...

K.

[LateLesley]

I found this which might be helpful to you. https://fccid.io/BEJIPS237LY/Schematics/BEJIPS237LY-Schematics-1715884

The backlight could be a bad CCFL or bad LED depending on how it's backlit. There are video's on youtube on how to diagnose backlight faults, and repair them. Some repairs aren't for the faint-hearted though, as it can involve taking the screen itself apart, and a high risk of damage.

It could also just be bad caps and high ripple on the supply. You could test the ripple by measuring the supply on AC Volts, and that should let you see the ripple. Any more than a couple of hundred millivolts, and i'd be checking the PSU for bad caps.

Anyway, welcome to the forum, and good luck with the repair.

[Homercleese]

Thanks very much for all the input guys and gals. I had been reluctant to crack the power brick knowing how destructive it usually is but it looks like that should have been the first area of investigation. Found a heavily swelled 680mu 25v cap, replaced and everything seems fine again.

Thankfully my mucking around with the LCD internals doesn't seem to have caused any damage either!

Thanks again.