Sony 55X900E no standby light, no power. Replaced mainboard already

[noinimod]

No standby red light, nothing
This Sony has a separate AC->DC power adapter supplying 19.5V to the TV power board (JK3)



Disconnected JK3 power board from main board, checked voltages on all the pin outs

At a few pins I can see the power supply providing 19.5V to the main board



Based on the service manual triage.. it seems to be pointing towards the power board (JK3) being the most possible culprit


LED light turns on when I disconnect LED driver board ribbon from mainboard (so i thought it is the mainboard, since i've read previous posts stating it's this).

Some more questions

1. Does the 12v supply to TCON only turn on when the power button is pressed on? Though i pressed the physical power button and could not see any voltage on the TCON pins (on the JK3 power board)

2. I can’t find the standby power pin on the JK3 board power diagram. None of the power supply pins give a 3.3V / 5V output. Not sure if this is the problem

Which brings me to.. it seems strange that there’s 19.5V output to main board, but no 3.3/5V output

4. Have already swapped the main board, but doesn’t seem to work. I bought from a reputable seller with good feedback from other buyers, but still can’t rule out the replacement mainboard is faulty

I attached more pictures below with details, hope to learn more from all of you. Is there anything else I should check? Thanks in advance

I extracted the diagrams from the service manual, link below:

https://cdn.badcaps-static.com/pdfs/...a35a4a7998.pdf

[dskall]

Re: Sony 55X900E no standby light, no power. Replaced mainboard already

Can we get good picture of board? Your replacement board had exact same problem? If so you may need to load your power supply and make sure it supplies under load.

[lasantha93]

Hi All,

I have the same issue as mentioned above.
I am also getting about 19.5 in CN9000 left and right pins. To be clear with the flow does 12V send to TCON (from JK3) board only when TURN ON the TV ? (I saw turn on switch is connected to motherboard and motherboard send signal to jk3 to turn on tcon so that it can send 12 V)

Does anyone have schematc diagram for jk3 board so we can check load under each ?
I saw there is a IC (ACTN 7D14) in jk3. Does anyone got datasheet for this ?

Thanks a lot

[nomoresonys]

Hi All,

I have the same issue as mentioned above.
I am also getting about 19.5 in CN9000 left and right pins. To be clear with the flow does 12V send to TCON (from JK3) board only when TURN ON the TV ? (I saw turn on switch is connected to motherboard and motherboard send signal to jk3 to turn on tcon so that it can send 12 V)

Does anyone have schematc diagram for jk3 board so we can check load under each ?
I saw there is a IC (ACTN 7D14) in jk3. Does anyone got datasheet for this ?

Thanks a lot

Post good focused pictures of each board and one of the whole back as to see how everything is connected.

[lasantha93]

Hi,
Thanks for you reply.Please find the below photos attched

1. Back of the TV




2.Motherboard



3.LED Driver board



4.JK3 Board



5.Tcon Board


6. IR Sensor Board




7.TSA board



8. Wifi Module Board


Thanks

[nomoresonys]

Ok, you say there's 19.5 on the connector at two pins of CN9000 of JK3 board, did you trace that voltage thru the wires out, see if it stops or actually gets to the mainboard. Maybe check all the fuses, some can be very small on sonys, did you check the little white fuse on the led driver board.