Sony kdl-42w705b

[jonny78]

hi guys posted a few days ago about this set..suspected a bad panel but i decided to go ahead and change the tcon board as ive read this set is known for bad tcons...attached is how the tv looked with the old tcon! ive replaced the tcon and now i get a completely different picture...tv turns on backlight is on but its a blank screen..wouldnt the screen be exactly the same if it was a bad panel regardless of the tcon?

cheers the for the help guys!

[kgavionics]

Re: Sony kdl-42w705b

hi
just check the connection between the main panel and the tcon board.

[budm]

Re: Sony kdl-42w705b

Did you put the old T-CON board back in to see what you will get now? The panel may have taken out the new T-CON or the new T-CON is defective or not the right one. I would also try having one cable between T-CON and the LCD panel connected one at a time to see what you will get.
Also verify that you put the cables back in place properly.

[jonny78]

Thanks for you reply.. The new tcon is from a reputable dealer and is identical to the old one...the original tcon when disconnected from one side the shows a perfect picture on one side and a blank picture on the other.. I've read this means it's a bad panel right? I suspected a bad panel as soon as I received the set but as I got it for free thought it might be worth trying a new tcon to fix the problem....Would it be a tab bonding problem which has caused the panel to go bad? I recently fixed a Samsung series 5 with tab bonding problems and after 3 months its still going strong..! Thanks for the response!

[budm]

Re: Sony kdl-42w705b

"the original tcon when disconnected from one side the shows a perfect picture on one side and a blank picture on the other.. I've read this means it's a bad panel right?" Yes, you have problem in the panel some where, you can start by check the resistance of those caps on the tab bponding boards to see if any of those caps shorted out or showing very low resistance readings. It can also be due to bad TFT driver ICs attached to the flexible PCBs,

[jonny78]

Re: Sony kdl-42w705b

Thanks for you reply! took the tv apart today to expose the tab bonding strips.. no shorts on the tab bonding boards..theres 6 on this panel all at the bottom and the far left one is insanely hot..actually burnt my finger..touched this gently in different positions to try and get a reaction out of the screen but nothing changed! should it be this hot ? the others are more than touchable but this one is red hot! would it be worth trying to make this cooler with the varierty of temporary fixes people have used?

regards!

[budm]

Re: Sony kdl-42w705b

You are talking about TFT driver ICs on the flexible PCB, right? Sounds like they are bad.

[steves7839]

Re: Sony kdl-42w705b

Let me add one other possibility, if your backlight came on but no picture with the replacement TCon. I just opened a KDL52S5100 with this symptom. The TCon has a shorted power rail because VCC_1.8 reads 0 ohms to ground. ALSO, the Main Board fuse supplying power to the TCon is open. You could easily have both, and installing a good T-Con would still give you the backlight but no video symptom.

I would want to resolve this before TS the tab bonds; IME (in my limited experience) they often run hot while working.

Not to question the extensive experience and participation of BudM.(Thank you sir!)...but getting a good half-picture with one panel ribbon disconnected means either the panel or the TCon could be faulty.

[budm]

Re: Sony kdl-42w705b

When you can get half the screen working with only one cable connected but when both cable are connected you no longer get the pictures, it means something in the panel has loaded down the power supplies on the T-CON BOARD, you can verify that by check the VGH, VGL, ect, Voltages when you can get one half of the screen to come up properly, then try again with both cables connected and see if all the Voltages are still normal.. I would not have both cables connected for too long when you testing the new T-CON because you may damage the power supplies on the T-CON board.

[maleksa]

Re: Sony kdl-42w705b

I am having a similar problem on my SONY KDL-50W704A. For this model, the T-CON appears to be on the same board as one of the two buffer boards. When both boards are connected, the whole screen flickers badly. But when I disconnect one of the buffer boards, I get a perfect picture on one half of the screen, and blank on the other half. Any thoughts?

[Hamie]

Re: Sony kdl-42w705b

Bad panel I'm afraid

[maleksa]

Re: Sony kdl-42w705b

Bad panel I'm afraid

Thanks Hamie.

Sorry for this rather silly question, but what does it mean when a panel is bad? Is it the screen only that is bad or would it also include the circuits that is connected to the screen (i.e. anything after the T-CON)?

[attainteddragon]

Re: Sony kdl-42w705b

it could be the pcb that attaches to the panel, the ribbon that joins that pcb, the cof chip which is on that ribbon cables or the attachment point of the cable where it joins the panel.

[maleksa]

Re: Sony kdl-42w705b

it could be the pcb that attaches to the panel, the ribbon that joins that pcb, the cof chip which is on that ribbon cables or the attachment point of the cable where it joins the panel.

Thanks! This is really helpful