LG FoggyVision

[kf4rca]

Picked up this LG 42LF11 from the roadside. Its a 2013 model and, I believe, the last of the flourescent backlight models.
Anyway, it has a foggy picture. I have never seen this effect before. The backlight seems to be working. The contrast and brightness controls show some effect.
Every now and then it pops into normal. Doesn't appear to be a loose connection though.
It appears to have come from a very smokey environment, like a bar. (Cleaned it up as best I could.)
Anybody ever seen anything like this before? Thanks.

[JohnCT]

Are the vertical bars on the left side part of the picture or are they a reflection?

John

[MadMan]

If you put brightness on max, how much light overall is emitting from the screen? If the overall light level is low, the backlights are probably weak or one's not working. If light level is normal, this set might just have so many hours on it that the lcd is weak.

My best guess, anyway.

[kf4rca]

This looks like what it is doing:
https://www.youtube.com/watch?v=OvpZyYfdpWw
Thanks all!

[JohnCT]

Originally Posted by kf4rca

This looks like what it is doing:
https://www.youtube.com/watch?v=OvpZyYfdpWw
Thanks all!

I'll assume that the vertical lines shown in your first pic were reflections. If you have vertical stripes on the screen, the rest of this won't apply:

I've changed a hundred of the AS15 chips on TCON boards before (as shown in that Samsung youtube linked video), but I never saw one become intermittent like that. But one thing I've learned in the 50 years I've been in consumer electronics is that I haven't seen it all, nor will I.

Usually, the AS15 chip failure presents one of three ways: the picture is washed out and faded, or the picture is "overexposed" with too much contrast (severe gamma error), or the picture starts out normally and degrades quickly over a minute or so. The last symptom being restored with cold spray.

I have never seen one become intermittent where it will be crappy and then snap back to normal. If yours seems to turn on reliably but cut out after a few minutes, you can try freezing the AS15 chip on the TCON to keep the picture running. It it does, replace the TCON or the AS15 chip if you're comfortable doing SMD work.

Also, the AS15 chip runs just slightly warm under normal conditions. You can test this by putting the back of your finger between the first and second knuckle when it's running (all TCON voltages are low voltage - quite safe) and see if it gets hot. If you feel a sharp rise in temp on the back of your finger, the chip is bad.

John

[kf4rca]

Thanks. Sorry for being late getting back to you. The AS15 chip is on the VOCTL board rather than the TCON board.
I've done some SMT work but maybe not as fine pitch as this is.
There seems to be several versions of the chip out there-all with different suffixes. What is the difference and are they interchangeable?
They have an AS15 chip in stock at the local AudioLab for $6. They used to do video work too but now only do audio repairs.

[JohnCT]

Originally Posted by kf4rca

Thanks. Sorry for being late getting back to you. The AS15 chip is on the VOCTL board rather than the TCON board.
I've done some SMT work but maybe not as fine pitch as this is.
There seems to be several versions of the chip out there-all with different suffixes. What is the difference and are they interchangeable?
They have an AS15 chip in stock at the local AudioLab for $6. They used to do video work too but now only do audio repairs.

Electrically they're the same, but there are two different case versions: one is all plastic and the other has a metal bottom. Otherwise they have the same exact dimensions and pin pitch.

Because the metal bottom is soldered to the PC, the metal bottom chip has to be removed with hot air. The all plastic version can be removed with hot air or a low temp alloy like ChipKwik from the top.

I generally stock the metal bottom one as it will sub either, but some PCs have some feed through holes below the chip so the metal bottom one might short to the feed throughs on the board, but that's rare.

If you go to Alibaba and enter your exact part number, you should be able to see which one you have by the picture. Check several vendors in case one is using a stock photo.

If it's all plastic, it's far easier to change than the one with the metal bottom.

I've never done it, but several techs have told me they used the plastic chip in place of the metal bottom version. They put a dab of heat sink compound between the chip and the board and they say they will work. It's not a high power chip so I would think they'd be fine.

Now, I was buying these in lots of 20 for a few years from Alibaba, but occasionally got bad batches. I then used TSL1014 from Digikey for the plastic versions and they worked great, no failures. These have plastic bottoms. I've never gotten bad semis from DigiKey ever, so that's no surprise that I never had a new one fail. I used my supply of 1014s up and have a couple of metal bottom AS15s left from an earlier China order, and these seem good, but I think it's been a year since I last used one.

Since these TVs are older, the repairs on that vintage is drying up. I'll reorder the TSL1014s from DigiKey if I run out and get another in to repair.

EDIT: Now that I think about it, I recall some chatter about a suffix version of the AS15 that was not compatible, the E2 IIRC. So if you have a AS15F, or G, or any single letter suffix, they will all interchange and you will be fine - avoid any version with a number in the suffix. I don't recall ever seeing an E2 but if you get an E2 sub, it won't work.

John

[kf4rca]

Thanks for all the great information. I'll go by AudioLab this morning and see what they have.
Thanks again!

[kf4rca]

I ordered a board from Ebay. Only $15. Seems to work well.

[JohnCT]

Originally Posted by kf4rca

I ordered a board from Ebay. Only $15. Seems to work well.

Let's see: pay $15 for a working board or $10 for a chip and spend a lot of time installing this surface mount device and possibly having to remove it and reinstall it should some solder underneath the chip drifts across adjacent pins...

I'm going to make a summary judgement call here and just call that a flat out WIN!

BTW, that generation of LCD/CCFL flat panel will outlive an LCD/LED TV by 10X going by what I see in the shop every day.

Yeah, they're thicker and heavier, but they are workhorses. Other than the typical electrolytic venting on the power supply (easy fix), these are very reliable.

Enjoy.

John

[kf4rca]

I figured it was worth a $15 board.
I've noticed the newer sets are one board wonders.
My latest roadside find is an Element ELEF408 (Wallmart brand) that won't turn on. And its a one board set.
This one weighs maybe 20 lbs. So they're getting lighter. And cheaper.

[JohnCT]

Originally Posted by kf4rca

My latest roadside find is an Element ELEF408 (Wallmart brand) that won't turn on. And its a one board set.

Those are "Black Friday" promo models. They combine the main, the power supply, and the TCON in one board (although some versions put the TCON circuitry on the bonded (and not replaceable) scan boards that are part of the display screen.

If you get 160V across the big black cap and it doesn't respond to the power button, it's probably a corrupted eeprom. That's that 8 pin chip near the largest chip on the board. It will have a "25" in the part number.

I fix those by removing the eeprom and reflashing it with a cheap TL866 programmer.

If you look for a board for it, you must be SURE to make sure it's exact! They all look the same but there are subtle differences in the connectors, and the board you get may not connect to the wiring in the cabinet. Use the close up pictures available and enlarge if you have to.

John