Sony KDL55EX720 won't turn on

[tibimakai]

I have just picked up this TV and the owner said that it had 5x error blink. When I was picking it up, plugged it in, the TV it was completely dead.
He said, that a technician looked at it and he told him, that a board has to be replaced and it will cost him $350. He decided to sell it.
When I got home, I have found a plug which is the IR sensor, power LED, side buttons plug it was disconnected from the mainboard.
By reconnecting it, nothing has changed.
I have noticed that it doesn't have a STBY 3.3V present.
The 170V at the main caps is present, I can measure a 4.46V at a diode(D6251) next to the output connector. It is across the transformer's output.
I'm not sure where the standby stage is, it would be T6201? It's a transformer with yellow tape on the winding at the bottom middle of the board.
I didn't have time yet, to take pictures, but I wanted to get started with it.
Here is shopjimmy's picture until then:
http://www.shopjimmy.com/sony-1-474-303-11-g6-board.htm
Any help would be appreciated.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

I have found the service manuals(there are 2) on elektrotanya, but unfortunately the power supply is a very low resolution, most likely they did this, to don't be visible.
There are no parts lists either, about the power supplies.
I have found something, very similar on elektrotanya, it's a 1-883-922-11, mine is 1-833-922-12.
There is a RJJ0319 and a CXA3799AM on the underside of the PS.
Unfortunately, my daughter is sick, and I'm alone with her. So, I can't work on it today.
I'm attaching the schematic, if anybody would like to look at it.

[R_J]

Re: Sony KDL55EX720 won't turn on

On Power supply board, Check Q6101 and Q6102 mosfet's for shorts, and check R6540 fuse resistor (.1ohm) for open

[tibimakai]

Re: Sony KDL55EX720 won't turn on

Thanks for trying to help.
I have checked them and they seem fine.
I think that we should concentrate on the standby stage first.
If the standby stage is not working, nothing will turn on.
I don't have much time today, because it's Easter, but next time when I get the chance, I will look at the CXA3799 IC.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

I have found something that I don't think that is good.
There is an IC 6251 which is a 3.3V VDO with turn on/off control and it supplies 4.27V right now.
In the schematic above, it looks like this regulator should provide the STBY 3.3V.

Should I replace it?
There are some differences, between the schematic and my board. The 4.27V doesn't reach the STBY pin at the connector, there are 0V.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

Somebody can confirm that T6201 is the standby transformer?

[budm]

Re: Sony KDL55EX720 won't turn on

Yes, it is for the 3.3VSTBY power supply.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

Thank you Bud.
If I apply 3.3V at the connector's pin(with removed wire) the TV shouldn't boot up?

[budm]

Re: Sony KDL55EX720 won't turn on

I did not study the circuit in full details yet to see how it functions.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

I can't find the datasheet for CXA3799 IC. I'm wondering what kind of voltages should have at each pin?

[tom66]

Re: Sony KDL55EX720 won't turn on

Any schematic of its usage?

[tibimakai]

Re: Sony KDL55EX720 won't turn on

In post#2 it's a schematic of the PS. It's not exactly the same, but it's usable.
It is located in the secondary side of the PS.

[tom66]

Re: Sony KDL55EX720 won't turn on

It looks like some kind of microcontroller, so I'm not sure, it depends on the program it is running.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

Do you think, that it has anything to do with the STBY missing? To me, it looks like it shouldn't affect the STBY voltage.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

These are the voltages that I'm getting at the PS connector CN6101:
Power_On= 0V
ACC_Off_Det= 0.495V
Bl_Error= 0.131V
T-Con_On= 0V
STBY3.3V= 4.267V
AU_12V= 0.003V
Reg_12V= 0.003V
BDR_ASU_12V= 0.001V
T-Con_VCC_12V= 0V
I think that I made a mistake last time, I have measured the wrong row of pins.
The stby is 4.267V, which to me it looks like it's to high.
There is no power on voltage coming to the power supply though.
STBY LED doesn't turn on either.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

I have jumped with a resistor the STBY to Power_On and I have 391V at the main caps, I have AU_12V and REG_12V, there is no T-Con_VCC_12V though.
391V goes to the G8(small PS) There is 12.71V and AC_Off_Det 4.4V at CN6102 connector.
It seems like the mainboard is not sending the Power_On signal, but I would like to see the screen that it turns on and everything it's fine before I would spend money on this TV.

[budm]

Re: Sony KDL55EX720 won't turn on

You need another resistor between STBY and T-CON ON to turn on the power supply for the T-CON, you can see how it works in the SCH for the 12V T-CON power section.

[tibimakai]

Re: Sony KDL55EX720 won't turn on

With that resistor, the LEDs should turn on?

[budm]

Re: Sony KDL55EX720 won't turn on

AC det out pin 26 of IC6501 (CXA3811): from spec sheet of the IC:
The AC_DETOUT pin is the output signal for this function, and outputs High when the AC input state is normal,
or Low when AC OFF or other abnormal state is detected. Changing “L” to “H” of AC_DETOUT pin requires
detecting "C" period one time or remaining in "C" period 10ms or more.
So check the DC voltage on that pin 26. It sounds like it is sitting HI right now which will make OPTO PH6302 OFF, which makes Q6402 to be OFF, so the Voltage on the Collector of Q6402 will be HIGH which makes the AC OF DET PIN 7 of CN6101 on the connector to be HI as you have measured, so that is normal . Read the spec sheet and see the SCH for details.

[budm]

Re: Sony KDL55EX720 won't turn on

"With that resistor, the LEDs should turn on?" What LED? The resistor I talk about is for turning on the T-CON power supply. We did this exact same thing on the other SONY you worked on before. Right now you main board in not sending PS_ON, or T-CON on, sounds like the other SONY that you replaced the main board twice.