Sudden gray washout - panel? controller? worth fixing? - AVS Forum
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post #1 of 9 Old 04-28-2010, 07:32 AM - Thread Starter
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Greetings all,

After nearly 4 years my LVM-42W2 (Westinghouse) has finally given me a problem. I am hoping/thinking that it is worth fixing - and if it is something as simple as a board replacement I can do that easily enough... but need some help in diagnosis. I looked through existing threads on the LVM series and found nothing like this, and would really like to try self-diagnosis before giving it to an expensive repair shop who will charge me up the wazoo just to tell me it can't be fixed.

2 nights ago I turned it on and was greeted with a heavily washed out screen - almost as though the brightness and contrast were completely out of whack:



This happens across ALL inputs - even ones with null signal or nothing connected, and also while switching inputs... at no time does the washout dissipate:



I also notice that there are columns of flickering pixels in the infobox that appears when switching inputs, and have verified that these are not present at any other time other than when this box is up on the screen, and they are not dead pixels - they are perfectly fine with other solid colors from an external source. You can't see here as it is a freeze-frame, but to the eye they look like long, black lines through the box, and flicker on and off in different sections at random:



Something that is really interesting is as soon as I enter the menu for the tv - the screen darkens significantly, losing a lot of the washout effect, and stays that way - EVEN when I exit the menu. With further, extreme adjustment I can get it to a watchable level, but the color saturation is way off, and there is still plenty of gray washout. In addition - any dark areas like the top and bottom letterbox bar and the lower-left corner where the image fades to black flicker at random intervals.



I am not thinking it is the panel itself - because it does darken in the menu, and those pixels only appear to flicker when that one box appears... I figure it is a board or controller or something else - but have no idea what/which and would hate to start throwing parts at it if it is a lost cause, or have it end up being the last part I replace, ya know?

Would appreciate any info/feedback from people who have had any similar experiences with their own panels.

Thanks!
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post #2 of 9 Old 04-28-2010, 01:37 PM
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It is always quite simple:
Trace the signal chain from either LCD panel back towards the AV processor board, or trace the signal path from the AV processor board towards LCD panel. Whatever works for you and whatever you feel more comfortable with.

In your case I think you may have faulty T-CON board. However, to narrow down the cause of the problem:

1. Check the power supply for obvious signs of burning, discoloration and bulged capacitors. If you have multimeter, measure the voltages at various connectors to see if they are correct (voltage rails ratings are usually printed on components’ side of the PCB).

2. Check the connectors between T-CON board and LCD panel. Remove the ribbon cables and clean all contacts. Use hard pencil rubber and clean the exposed copper contacts until they are shiny again. Re-assemble everything and turn ON the TV.

3. If you see TAB being utilised on your particular LCD panel, re-apply the pressure on bonds’ area and see if the picture restores to normal. If it does, try to use something (rubber or soft plastic strip) that will put the pressure on bonds’ area once you close the TV…. and never but TV that utilises TAB process to feed the signals from T-CON to LCD panel.

4. Remove the cables between AV processor board and T-CON board and clean them well. See if that fixes the problem.

5. If you are still getting the same problem -> replace the T-CON board.

Do I need to warn you about lethal voltages inside the TV?

Good luck,
Boky
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post #3 of 9 Old 04-28-2010, 02:06 PM - Thread Starter
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Quote:
Originally Posted by Extreme_Boky View Post

Do I need to warn you about lethal voltages inside the TV?

Nope... but maybe explain T-CON and TAB just a bit so I know exactly what I am looking at/for. (I assume t-con is the controller board... but T = ?)

Thanks for taking the time to respond and give me some info. I was planning to crack it open and clean/re-seat everything I could anyhow... but figured I would also post up here and see if anyone has an inkling as to where I could start or if they have seen anything similar. From what I can tell without opening it - there is a main board which seems to have all the I/O interfaces, a controller board, an inverter board and a power supply.

Thanks again, I do appreciate it, and will respond with what I see happening as a result.

-scr
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post #4 of 9 Old 04-29-2010, 03:56 AM
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T-CON stands for timing control board. It is a PCB that does motion interpolation. It consists of fast memory chip(s) and a capable processor. The processor uses LVDS signals (differential - immune to noise with good drive capability) coming from AV board and interpolates an extra frame based on two contiguously received frames received from AV processor - hence the dreaded input lag issue

Many faults can be fixed purely by cleaning oxidised copper contacts, so do that first. Sometimes it is even enough to remove the connector from the socket, and then to re-insert it. This usually breaks the oxidation and re-establishes good connectivity.

The TAB process is a way of bonding bare exposed contact to the LCD panel substrate. Very often, like in almost all Sony TV's, these contacts develop large resistance that produce intermittent problems that change with temperature. Re-applying pressure on the bond's area can easily fix the problem in a way that the TV may be working again for many months. Check the photo it clearly shows the affected area.

and I also attached the T-CON board photo from my Sharp TV. The LVDS (from AV processing card) and T-CON to LCD panel ribbon connectors are clearly labelled. Processor is little square thing in the middle covered with heat conducting pad:


Boky
LL
LL
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post #5 of 9 Old 04-29-2010, 06:40 AM - Thread Starter
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Sounds good - thanks for the further info. I will crack it open and give it a go this weekend and report back what I find.

Appreciate the help !
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post #6 of 9 Old 05-07-2010, 09:57 AM - Thread Starter
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So after taking a couple hours to slowly pull it apart, I inspected the PS, mainboard and what I believe is the t-con board for swollen caps, burns, etc and found nothing. I then cleaned and re-seated all the ribbon cables... over a dozen of them... plus all other contacts - and repeatedly re-connected them all.

Modern ribbon cables aren't much thicker or stronger than a human hair it seems... and I was really bracing myself for an all black or half black screen, and almost relegated myself to having to purchase a new display.

Low and behold I power it up - and can tell immediately when the "no signal" box pops up prior to HDMI sync that my grey washout is GONE. Also no flickering pixels like in the shot above.

After resetting everything back to where I had it before - it looked spot on to how it was prior to the washout incident.

Total cost... a couple of hours of my time.

Damn I love it when that happens.

Thanks for the feedback prior to me embarking on this.
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post #7 of 9 Old 05-07-2010, 10:04 AM
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They asked you to check the power supply for bad capacitors! Bad capacitors is common in generic TVs due to small power supplies made power supply to run hotter. They will bulge.

Cheers, Wizard
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post #8 of 9 Old 05-07-2010, 01:47 PM
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Great!

You should also notice that colours look better and the picture in general looks great - now that you removed contact resistance from the connectors.

There are many who don’t believe that contacts surface oxidises and looses connectivity. The reality is that around 30% (or more) faults in modern LCD TV’s can be fixed just by cleaning all contacts.

This is why I recommended contact clean first before proceeding to module replacement.

Boky
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post #9 of 9 Old 11-30-2010, 08:20 PM
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@Srobak: I had my LVM42w2 apart, and did not see a T-CON specifically, but did notice what is referred to by some ebay sellers as a 'lcd mainboard', the board mounted in the middle-back with all of the input connectors soldered to it.

Did you have to tear down below this to reach another board (the T-CON?). I'll probably tear mine down again just to check, but wondering how many boards (not backlight inverter related) you had found in your unit when you cleaned it up.

Thanks!
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