Question About TCon Board Failures

[kf4rca]

How do they fail, in particular for Samsung?
One side lines and the other OK.
One side black and the other side lines (or OK)
Both sides black (or lines)

Found this link for advanced troubleshooting techniques. (Click on download.)
https://www.pdfdrive.com/lcd-led-tv-...e48676743.html

[JohnCT]

Most TCON boards fail with two general symptoms: either no picture or a very bad picture. Occasionally we'll see one with vertical strips either over the picture or instead of a picture.

On older models, the AS15x chips were common. I used to order them 50 at a shot out of China. But like VCR repairs, they dried up almost overnight. I just put an AS15 chip in an older Sony for another dealer, but that's the first one I changed in over a year.

Newer Samsungs (5-7 years) have DC-DC converter ICs that fail. Like the AS15, they are surface mounted and have to removed with hot air because they have a bottom metal pan that serves as ground and the heatsink.

Multi layer chip caps are common failure items, and they generally short hard over. These are small brown bricks (look like tiny Snickers bars) and are usually installed with two to six in parallel. With the ribbons to the display disconnected, check for voltage on any inductor you find on the board. Generally speaking, every inductor should have a voltage on it. If a voltage is on an inductor with the display disconnected but disappears when the ribbons are reconnected, you have a shorted chip cap or COF chip in the display. If you find no voltage on an inductor with the ribbons disconnected, check for shorted multi layer chip caps.

John

[kf4rca]

Thanks. How about driver board issues? Doesn't seem to be much electronics on those. Why is the left board different from the right?
What do you think of those panel testers?
https://www.ebay.com/itm/New-LVDS-Pa...0AAOSwCtxfPgjX

[JohnCT]

Do you mean the bonded boards between the display and the TCON? We call them address boards although I'm not sure that is a good definition either.

Those are often symmetrical and sometimes not, depends on the whim of the manufacturer. Those that are symmetrical and have two ribbons are almost like two different screens side by side. In those, you can get half a normal picture with just one ribbon connected. If removing one side restores the picture on a TV that shows none, the disconnected side is bad. That can be a problem on the address board, or a bad COF chip on the flexible ribbon, or a COF chip on the side tabs of the display (usually hidden by the front mask).

We see a lot of newer screens that are not symmetrical at all. New Samsungs and some others have a 25 series eeprom on one side. If the main board polls the display and doesn't get back a good answer, the TV shutsdown and recycles. Many modern displays won't run with just one ribbon disconnected, either having no picture or causing a shutdown. Worse, many cheap TVs (like Black Friday toilers) combine the TCON with the display address boards, so we have to work on the "TCON" right on the display screen. Sigh..

As far as that LCD screen tester, they probably are better for laptops where computer manufacturers don't want anything to do with screen design but just pick a vendor and design their video circuits to match, so there's probably far fewer unique designs available in laptops or computer monitors. Those testers won't help where the TCON is actually part of the display.

I don't know of any professional TV techs working today that have one of those testers, although one of my friends with a computer store has one. I can't conceive of any tester possibly covering every contingency of TV panel manufacturer.

John

[kf4rca]

Got a 40" LED Samsung with a TCon board that has the 3 LEDs on it. Two of the leds are out. From what I read, that means a panel short. If I disconnect the right ribbon cable all leds stay lit. BUT I can reconnect the ribbon cable (while powered up) the leds stay lit and I get lines both sides.
This was, as you probably suspected, a road side find. So, what do you think? Thanks.

[JohnCT]

Originally Posted by kf4rca

Got a 40" LED Samsung with a TCon board that has the 3 LEDs on it. Two of the leds are out. From what I read, that means a panel short. If I disconnect the right ribbon cable all leds stay lit. BUT I can reconnect the ribbon cable (while powered up) the leds stay lit and I get lines both sides.
This was, as you probably suspected, a road side find. So, what do you think? Thanks.

Depends on the model. If it's a fairly new Samsung, it could be anything.

Ordinarily, disconnecting the offending ribbon would allow the good side to work on half a pic, but that's not true all the time. What I would do is watch the small square inductors for voltage. If you find one or more without voltage, remove the ribbons and restart the TV again. If the voltages come back and stay up, it's probably a shorted display panel.

A hack repair is to identify the bad side, remove the mask from the display, and *carefully* cut all the *side* tab flexible circuits off the display with a brand new safety razor or xacto (you do NOT want any pulling on the ribbon as you cut). The drivers on the good side of the board will usually drive the entire screen all the way across and look as if nothing happened.

If it's a display that shorted, you have nothing to lose by trying it.

Now, many newer TVs don't have side tabs: they drive the X columns using the drivers that share the Y drivers on the bottom, and the printed circuits inside the glass. If you have one of those, let me know. There's a hack for that but it's more involved.


John

[kf4rca]

Don't think it has side tabs. But I'll check again,