LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/L !

[reessi]

Hi everyone,

This TV had the well known power supply issue, took ages to turn on etc until one day it never turned on, I removed and tested all output caps on the PSU with an ESR meter and replaced the ones I've marked in blue on the photo (they are the new ones).

After this it turns on fine but no signal is displayed when selecting VGA or HDMI 1 & 2 but the laptop always correctly sees the tv and brings up the name and resolution...

My new flatmate assured me the hdmi's had previously worked after waiting a long time for the TV to turn on but he hadn't used it for at least 5 years.

Other issues:

Sometimes it crashes! When changing inputs or plugging cables in the no signal disappears and screen remains blank with backlight, nothing works after that.

I factory reset it and while it was searching new channels on reboot the screen went gargled and froze.

I rebooted and re-tuned and now DTV works fine including sound. Although not tested for ages, maybe it would eventually crash or flicker!

Backlight:

If watching long enough I noticed the no signal occasionaly distorts, you have to watching for minutes as it is quick.

Later I noticed from behind that this was in fact accompanied with the backlight flickering for a millisecond but you couldn't notice easily from the front unless expecting it.

I've tried heating the mainboard and specifically the genesis chip and the power supply board, it makes no difference.

I notice the hdmi and vga inputs go into the Main GENESIS chip so I'm airing to wards this being faulty and would explain it crashing....

But the backlight flicker, can this be caused from the mainboard too? I would expect that from the PSU?

I can pick up a mainboard online cheap enough but it is always more fun to understand and repair and also the backlight flicker throws me slightly!

NOTE - the DTV seams to not be affected by any issues after being on for 10 minutes.. but when I pressed input button screen went blank with sound... it didn't show input menu but after ten seconds it changed to HDMI input which I did not select as I only pressed input once and that only move it to next input (analogue tv).

Moving back to DTV now the screen was distorting and flickering but with sound...

Many thanks.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

I also checked the big electrolytic on the mainboard, I know it could also be the silver SMD ones but there are so many that I have not started checking these yet, I thought I would wait for other peoples advice... and heating them alot did not affect it...

[nomoresonys]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Could try a firmware update if you can find one.

[nomoresonys]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Could try cleaning and re-seating the ribbon cables from tcon to driver board and lvds cable from mainboard to tcon with isoprophyl alcohol.

[nomoresonys]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Did you try another device with hdmi besides a pc, like a dvd player etc? Sometimes the pc video card display settings conflict with the tvs, it's easier to troubleshoot with a different device.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Hi mate, I already did a factory reset which I mentioned and that it is where it crashed during the wizard.

I have already reseated all cables and I've just cleaned the LVDS to be sure and no difference.

I only have laptops available but I tried several and the result is the same.

I will look for a firmware update to try..

Many thanks.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

I couldn't find a firmware any where. I'll probably try buying a replacement board this eve if no other suggestions.

Cheers

[nomoresonys]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Probably a good call, those symptoms do seem like a mainboard issue.

[diif]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Second photo, the IC below the processor, what's that in the middle of it?

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Below on the photo or below when reading the writing horizontal on the chip - the one with the heatsink?

cheers

[nomoresonys]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

I think he's referring to the discoloration/splotch? on the IC just to the left of the Genesis chip, as you read it normally, think it says IC something 01, the one right next to where IC800 would be if there was one there.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

It's a ram chip -> HYB25DC256160CE

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

There is no discoloration/splotch, it just the way the camera took the photo!

[ReeceyBurger123]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Hdmi Ic I’ve changed a few recently.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

"Hdmi Ic I’ve changed a few recently"

I thought that but what about the vga? It goes straight into the main chip and all the other faults? Freezing etc?

Cheers.

[ReeceyBurger123]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

"Hdmi Ic I’ve changed a few recently"

I thought that but what about the vga? It goes straight into the main chip and all the other faults? Freezing etc?

Cheers.

I’ve also had ceramic surface mount capacitors and other surface mount capacitors fail on them boards too with high ESR. If you think it’s bad change it, I’ve waited months for Ics to come from Ali express it can be hit or miss. Testing can take hours too with a scope, narrow it down to the local supplies give it a check for short circuits on devices around that area.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

I've ordered a main board off ebay for £13 so I'll let you know what happens. I'll have a little play with this one while I'm waiting.. Cheers.

[reessi]

Re: LG 42LC55 - Fixed power fault caps, now NO input on HDMI & VGA, also freezes & B/

Replacement board came this morning in record time since I ordered at 4pm yesterday and I'm happy to report the tv is fully working.

So not sure why the mainboard failed, but re-capping the PSU and a mainboard has fixed it all.

Cheers.