LG 32LC2D-UD: Seizure-riffic!

[YamahaFreak]

I have been given an LG 32LC2D-UD flat panel television that has an unusual problem...the set powers on and technically runs okay, but at all times while it is on, the screen rapidly flashes colors in a seizure-inducing manner, along with lines and pixelation/artifacting that changes with the menus and displays onscreen. There is also a high-pitched hissing/whining coming out of the speakers that changes with the volume level, and disappears when the sound is muted or turned all the way down. Any ideas? This is an earlier flat panel from April 2006, and is quite dusty.

[YamahaFreak]

No ideas at all? I almost trashed this one, but couldn't bring myself to. I usually don't care with the flat ones...odd...

[rcaman]

remove the ldvs cable that goes to the t-con board and clean the contacts. the t-con is the board at the top center that drives the panel. the cable will come from the mainboard and connect to the t-con. see if that helps. the t-con or mainboard could be bad. steve

[rcaman]

also look closely at the 1000mfd caps on the power supply. or just change them. steve

[YamahaFreak]

Thank you, I will try those.

[YamahaFreak]

I am revisiting this set. Last night, I started the TV with first the T-Con disconnected, and then with the input board disconnected. Both times, the funky screen and sound persisted. (Obviously without a screen in the case of the disconnected T-Con) This means the mainboard is at fault, right? I can't imagine the backlight inverters could be causing this problem?

The TV occasionally randomly cleans up its act for a few minutes at a time, displaying a (nearly) artifact-free screen and clean sound, but it always reverts back to insanity minutes later. No obvious bad caps on the mainboard...but most of them are SMD caps and hard to 'read'.

Do you all think it's a reasonably safe bet that replacing the mainboard will solve the issue? I have my finger on the 'Buy It Now' button.

[dr.ido]

If this is the model I'm thinking of the 3.4V rail is quite critical. Bad caps in these are not always obvious and they don't always bulge. The 3.4V rail comes from a DC-DC converter IC fed from 6V rail. I've found bad SMD caps and resistors around this IC before.

Clean any gunk from the thermal transfer blocks off the back of the board if you haven't already. I suspect this may be what caused the SMD resistors/caps to fail.

If the power supply is known good then that only leaves the main board. If a used main board is cheap enough it's probably the way to go. Bad SMD caps can cause all kinds of strange problems, but I've also replaced loads of high ESR reading caps and the fault remained.

[YamahaFreak]

Originally Posted by dr.ido

If this is the model I'm thinking of the 3.4V rail is quite critical. Bad caps in these are not always obvious and they don't always bulge. The 3.4V rail comes from a DC-DC converter IC fed from 6V rail. I've found bad SMD caps and resistors around this IC before.

Clean any gunk from the thermal transfer blocks off the back of the board if you haven't already. I suspect this may be what caused the SMD resistors/caps to fail.

If the power supply is known good then that only leaves the main board. If a used main board is cheap enough it's probably the way to go. Bad SMD caps can cause all kinds of strange problems, but I've also replaced loads of high ESR reading caps and the fault remained.

Earlier today I managed to snag a good used mainboard via the auction site for the stately best offer of $15.

I didn't see any thermal pads in this set, save for one that sits between the large heat sink on the power supply and the inner steel cover. As for SMD caps...I always wondered how to replace them? I see no way of getting them off the board properly. And yes, I've never personally seen one that looked obviously bad from the outside. They must have good 'poker faces'!

[dr.ido]

There's usually a small square thermal pad that sits under the power supply and makes contact with the DC-DC IC. I've seen them go "off" and leave a residue on the PCB and components. If the power supply has been out a few times someone probably already removed it.

For SMD electrolytic caps I usually twist the body of the cap off with pliers, then heat the pads with the iron to remove the leads. Most of the time I just replace them with ordinary non-SMD caps. For the others I heat both ends and nudge them off.

They can visibly bulge or leak, but usually not. You need an ESR meter to test them.

[YamahaFreak]

I don't believe the power supply in this TV has ever had problems or been serviced, but I will remove it and look for that thermal pad, and clean the area up. Do you recommend I replace that pad?

[YamahaFreak]

Mainboard arrived today. Did the swap and the TV looks awesome! Fixed the problem completely.

After sitting on this one for so many years, I'm elated to see it finally working great again!