Backlights but no picture - No 12v to Tcon board

[Stuckster]

Originally Posted by budm

https://www.badcaps.net/forum/attach...2&d=1571874353

Emitter pin (Top) is connected to R125/C181
Collector pin (Middle pin) is connected to R126
Base is the bottom pin.

Thanks.

Emitter pin = 0.0v ON, 0.0v OFF
Collector pin = 11.5v ON, 0.0v OFF
Base pin = 0.0v ON, 0.0v OFF

[dick_barton]

This may be the layout for the smd transistor. The readings given for the base does not appear correct.

[Stuckster]

Originally Posted by dick_barton

This may be the layout for the smd transistor. The readings given for the base does not appear correct.

Do you mean that the 0v reading on the base pin means that that component is faulty? Or that you think I measured the voltage incorrectly?

[budm]

Originally Posted by Stuckster

Thanks.

Emitter pin = 0.0v ON, 0.0v OFF
Collector pin = 11.5v ON, 0.0v OFF
Base pin = 0.0v ON, 0.0v OFF

BASE is not being driven.
Check the resistance between GND and the Base pin.

[Stuckster]

Originally Posted by budm

BASE is not being driven.
Check the resistance between GND and the Base pin.

Resistance between GND and the Base pin is 3.3 measured at 200k Ohms.

[budm]

3.3K is not bad.
Right now you can try removing the LVDS cables from the main board first the try forcing on Q1 by connecting 100 Ohms resistor between GND and Gate pin and see if you will get 12VDC at Drain pin or not.
https://www.badcaps.net/forum/attach...2&d=1571874353

[Stuckster]

Originally Posted by budm

3.3K is not bad.
Right now you can try removing the LVDS cables from the main board first the try forcing on Q1 by connecting 100 Ohms resistor between GND and Gate pin and see if you will get 12VDC at Drain pin or not.
https://www.badcaps.net/forum/attach...2&d=1571874353

Hmm. I really appreciate your help, but unfortunately I don't have a 100 Ohms resistor, nor the experience to solder components to the board. So this might be getting beyond my abilities.

Is there some other way to simulate 100 Ohms of resistance between GND and the Gate pin? Possibly using the meter?

Failing that, how certain are you at this stage that replacing the mainboard would essential fix the TV? And if I put a new mainboard in, from what we have already diagnosed, what is the chance that there could be something feeding back from the PSU or the Tcon and damaging Q1 on the mainboard? Or is that very unlikely?

[budm]

Well, if you do not have the ability to solder the component on the main board then how are you going to fix the the board?
At this you know that the main board is not sending the 12V to run the T-CON, so there is nothing else you can do but replacing the main board with KNOWN WORKING BOARD.
You can take the board to the local repair shop and have them solder in the resistor for you.
Q1 is not being turned on by Q2 that is why we are trying to do force on with the resistor to provide the 12V to run the T-CON, if there is no problem with T-CON and other problems with the main board then all the functions of the TV should work, if not then you have more than just 12V to the T-CON board problem, so the only way to find out is to force on Q1 but since you do not know how to solder then it is moot point to do further troubleshooting the board. If force on gets the TV to function then we can use other signal to turn on Q1 instead but that will require board modification which you cannot do.

[Stuckster]

Originally Posted by budm

Well, if you do not have the ability to solder the component on the main board then how are you going to fix the the board?
At this you know that the main board is not sending the 12V to run the T-CON, so there is nothing else you can do but replacing the main board with KNOWN WORKING BOARD.
You can take the board to the local repair shop and have them solder in the resistor for you.
Q1 is not being turned on by Q2 that is why we are trying to do force on with the resistor to provide the 12V to run the T-CON, if there is no problem with T-CON and other problems with the main board then all the functions of the TV should work, if not then you have more than just 12V to the T-CON board problem, so the only way to find out is to force on Q1 but since you do not know how to solder then it is moot point to do further troubleshooting the board. If force on gets the TV to function then we can use other signal to turn on Q1 instead but that will require board modification which you cannot do.

Hey. My intention from the outset was to diagnose the cause so I could confidently return and replace the faulty board.

Is the fix you have suggested a temporary measure for further testing or will it actually fix the problem and if so if I'm able to get it repaired it is it ok to leave it like that permanently?

[nomoresonys]

Maybe try there, they indicate that they have 1 mainboard, I don't know anything about them, might want to look their record up: http://a1tv.com.au/TCL.html

[Stuckster]

Originally Posted by nomoresonys

Maybe try there, they indicate that they have 1 mainboard, I don't know anything about them, might want to look their record up: http://a1tv.com.au/TCL.html

Hi. Yeah I have enquired with those guys. They want $355.00 plus $22.00 postage for a new board! Hard to justify on a 4 year old set.

I can get a new board off Ebay for around $270, which is still pricey. So I first need to arrange a refund on the faulty board to obtain the funds.

Might have to learn how to solder pcbs!

[nomoresonys]

Ok, I guess they lied, in their ad it said, we are back in business, all parts are 120 dollars, there at the bottom: http://a1tv.com.au/index.html

[dick_barton]

The board you are working on that's failing to power the Tcon was one you've just bought?
The one you've just looked at in post#51 is you feel, too expensive to buy for a 4 year old set?

Even though the Tcon is not being powered with the mainboard you already have, do you have sound, can you change channels etc to try and work out if the rest of the mainboard is functioning?

Is this your own TV or are you repairing it for someone else?

[budm]

Post #1 I need to be 100% certain which board is faulty before I outlay money to replace it.
But it looks like he did outlay the money to get the replacement board to begin with, but I thought he did not want to spend big money on the board.
I have already determined:
- Tcon board not receiving any 12V.
- Mainboard only outputting 2.6v to audio/speakers
- Replacement PCB (no change)
- Replacement Tcon board (no change)

Bottom line, the replacement board we are troubleshooting is not sending the 12V either.

[Stuckster]

Originally Posted by nomoresonys

Ok, I guess they lied, in their ad it said, we are back in business, all parts are 120 dollars, there at the bottom: http://a1tv.com.au/index.html

Ha. Yes. When I was googling it took me straight to the page with the part. I never saw the home page. Will have to call them on it and see what they say. Thank you

[Stuckster]

Originally Posted by dick_barton

The board you are working on that's failing to power the Tcon was one you've just bought?
The one you've just looked at in post#51 is you feel, too expensive to buy for a 4 year old set?

Hey. No the replacement board I bought was from a private seller and was sold in "used working condition". Was trying to save some $$. Lesson learned I guess.

Originally Posted by dick_barton

Even though the Tcon is not being powered with the mainboard you already have, do you have sound, can you change channels etc to try and work out if the rest of the mainboard is functioning?

I can't see a thing on the screen. So I have tried hooking up an external audio source, but I can't tell if it's on the right input. Have tried cycling the source button to no avail.

Originally Posted by dick_barton

Is this your own TV or are you repairing it for someone else?

My own TV.

[Stuckster]

Originally Posted by budm

Post #1 I need to be 100% certain which board is faulty before I outlay money to replace it.
But it looks like he did outlay the money to get the replacement board to begin with, but I thought he did not want to spend big money on the board.
I have already determined:
- Tcon board not receiving any 12V.
- Mainboard only outputting 2.6v to audio/speakers
- Replacement PCB (no change)
- Replacement Tcon board (no change)

Bottom line, the replacement board we are troubleshooting is not sending the 12V either.

Hi Budm. To clarify. The replacement board I first bought was a used board. Was trying to save some money. Unfortunately it didn't work. Now that we have determined fairly conclusively that is faulty (with your generous help) I would like to return the used board so I can buy a new board.

[Stuckster]

Ended up returning the used board and received a refund through Paypal. Got the TV serviced and new mainboard installed. Repairs are warranted for 3 months. Thanks all for your help.

The moral of this story? Never buy used electronic components unless you can diagnose and repair them!

[budm]

Thanks for the follow-up on the repair.