Panasonic TX-42A400B

[vinceroger69]

Re: Panasonic TX-42A400B

I have not heard of that myself or even read about if im honest, is it possible the t con is a known issue on these sets and you have brought another faulty one? what is the lcd panel number used in this set? is it a panel with a known high failure rate? can you check if the main board is sending signals too the t con im sure i have read you can measure the twisted pairs of wires on the lvds lead.

[ronhayes]

Re: Panasonic TX-42A400B

Hi Vince
I have took some picture of the rear of set to show the labels and connections but unfortunately I cant measure for signals as my scope is to old for this type of work?

[dick_barton]

Re: Panasonic TX-42A400B

It may be worth trying to read as many voltages as possible marked on the TCON. There could be a fault on the interface strip between the panel and the tcon or even the COF chips that is loading or even shorting one of the tcon supplies.

[ronhayes]

Re: Panasonic TX-42A400B

Hi All
I have contacted the supplier for the item mentioned kindly by vinceroger69 and they inform me this tester can only be connected to the T-Con board and it only comes with 14 common TV connectors.
So if you need to test a TV screen it would be difficult unless you know 100% that the T-Con is working.
But having said that still think it would be a handy item for the work shop.
If you have no display and you connected this tester to the T-Con and you then have a display you would know that T-Con and screen are ok.
But if no display then it could either be display or T-Con that were faulty.
I have now sent for another T-Con for this set as they are not to expensive hoping this will give me some positive results.

[thoma]

Re: Panasonic TX-42A400B

http://forum.iwenzo.de/topic.php?t=6...ght=led;tester

[vinceroger69]

Re: Panasonic TX-42A400B

this pdf link is a training manual for a lg tcon maybe worth a read as does say how to check voltages etc on a tcon board
file:///C:/Users/LENOVO%20OWNER/Documents/Electronics%20Repairing%20Collection%20Ebooks/TCON%20TRAINING.pdf

[vinceroger69]

Re: Panasonic TX-42A400B

http://forum.iwenzo.de/topic.php?t=6...ght=led;tester

This is a good link for the back light led tester, the tester we have mentioned in this thread is too test the lcd panel/t con too prove the lcd panel is good as the back lights on this set seem too be working fine.

[ronhayes]

Re: Panasonic TX-42A400B

Hi All
this may be a stupid request but maybe someone could help !!
I have purchased the LCD test tool as recommended by Vinceroger69.
Now it has arrived and as you can guess the user instructions are quite vague to say the least.
It came with four discs but having trouble using them.
I have checked the video's on YouTube and have a good idea on how to use .
Now if some one could kindly look at the pictures I have attached to this message maybe they could help !!
There are only two connectors that fit the t-con board and as you can see number 1 has the power connectors on the right and number two has the power connectors on the left.
now looking at the service manual as kindly supplied by Dick_Barton on page 10 it states lcd screen is 1920x1080
And in the service manual there is no info on the t-con board but from when I tested the f1 fuse I got 12v .
So I am sure looking at the tester I think I would need to use the lead number one and set the tester to 12v and the display to 51,52or53.
If someone has used one of these before and can look at the attached pictures and confirm this for me it would be much appreciated.
I am going to print out the instruction when I manage to access the discs.

[dick_barton]

Re: Panasonic TX-42A400B

It would look like lead number 1 because as you say that lines up the fuse on the Tcon with what appears to be the supply wires (Red) of the connector. No 51, 52 and 53 match the screen resolution.

[ronhayes]

Re: Panasonic TX-42A400B

Thank you dick
I have now carried out the tests
I have done this test with three t-con boards and get the same results with all three no display back lights on but no colour bar displayed.
Now according to the test tool if no display t-con faulty if display colour bars then fault with logic board.
Now when I first looked at this TV I assumed the fault was the t-con board, So I sent for a replacement t-con board when this failed to give me a display I sent for another but still the same issue. now I find it hard to believe that three t-con boards are faulty so I now think that the LCD display is faulty!! now I know the connections are at the bottom of the TV and someone suggested that it could be water damage? I have looked very closely at the LCD boards at the bottom of TV and can see no signs of water stains at all.
It would seem the this LCD has just give up very strange this is the first I have looked at with this issue.

[attainteddragon]

Re: Panasonic TX-42A400B

have you tried applying pressure to the cof chips and connections to see if that alters the picture at all?

[ronhayes]

Re: Panasonic TX-42A400B

Yes I have applied pressure to all connections along both boards but not even a flicker!
I also unclipped boards from their position very carefully I must say as not to damage the connections to see if any water damage with magnifier glasses but all looked fine.
That's why I think the Lcd screen has gone down but must admit never had this before ?

[attainteddragon]

Re: Panasonic TX-42A400B

i suspect that it is panel, though not all will alter the screen when pressure is applied.
you might get lucky and find a shorted ceramic cap on the panel driver board, but that does not happen often.

[ronhayes]

Re: Panasonic TX-42A400B

Yes but there are two driver boards so if that happened you would get half picture on the other board ?

[vinceroger69]

Re: Panasonic TX-42A400B

with your new tester can you connect it up and disconnect one side of the ribbon cables from t con too panel pcb do you get the test patterns on half of the screen?if not try with the other side disconnected, caution though im not sure if your new tester will work like this so try at your own risk is you want too try it out

[dick_barton]

Re: Panasonic TX-42A400B

The only other thing I can think of is that the tester has been set to 12V and you can measure this at the LVDS tcon end. The data says the tester can be toggled between 3V3, 5V and 12V supply for the Tcon.

[ronhayes]

Re: Panasonic TX-42A400B

I have just tried toggling the tester through 3v3.5v and 12v and nothing on 3v3 nothing on 5v but when it goes to 12v you get a flash of colour at the top left hand side of the screen about 6" long and 2" wide for a brief moment ?

[ronhayes]

Re: Panasonic TX-42A400B

I have tested screen with removing connections from panel here are results !
Pict 1 is with R/H connection looking from back of set pict 2 is displayed for a split second then goes to pict 3 with the L/H connection removed as the tester is switched on

[dick_barton]

Re: Panasonic TX-42A400B

Sorry Ron but out of idea's other than cycling through options 51, 52 and 53 and see what happens

[ronhayes]

Re: Panasonic TX-42A400B

Yes I have tried that but same results I am convinced the LCD panel is shot.
But thanks for all your help much appreciated I will be carrying out that test on the Digihome tomorrow.