Sony KD-55X750F bricked, keeps rebooting

[alfatv]

Somebody messed up with this TV before me.
I got to the point where TV powers up, Sony logo appears, then animation, after that it powers down and all starts all over again.
Tried vol- and power buttons, running circle appears for few sec, then same as above.
Tried firmware update via USB, no reaction from TV.
I know it's main board, but what else can be done?

[nomoresonys]

Re: Sony KD-55X750F bricked, keeps rebooting

Kit here, as always make sure it's a match if you get it: https://www.shopjimmy.com/sony-kd-55...air-parts-kit/

[Davi.p]

Re: Sony KD-55X750F bricked, keeps rebooting

Only operating system handlings, but you must know basics of linux/android shell environment, too long to explain, and huge amount of luck to avoid access protections.. which are the steps you made in this repair?

[Diah]

Re: Sony KD-55X750F bricked, keeps rebooting

displaying the android animation mean the firmware which saved on NAND started, mean too bootloader / kernel started too. 2 reason could be for this reboot loop

1- corrupted firmware ( same way you did the hard reset by power and volume- insert usb flash drive formatted fat32 and the last firmware on it from 11.11.2020 PKG format...and most important the usb flash drive must be with MBR mode) try it many time dont give up..
2- bad sector on NAND ( Freez it to bypass the loop ) or bad BGA if some one work on it.

[alfatv]

Re: Sony KD-55X750F bricked, keeps rebooting

Only operating system handlings, but you must know basics of linux/android shell environment, too long to explain, and huge amount of luck to avoid access protections.. which are the steps you made in this repair?

The first problem was with flex cable between main board and T-Con. Was not delivering power to T-Con. Added some scotch tape, good for now, will buy replacement cable once things are more clear.

I didn't mess with file system, but not sure what was done before.
Is there any way to hook up PC to this TV? Would be interesting to see at least boot log.

[alfatv]

Re: Sony KD-55X750F bricked, keeps rebooting

displaying the android animation mean the firmware which saved on NAND started, mean too bootloader / kernel started too. 2 reason could be for this reboot loop

1- corrupted firmware ( same way you did the hard reset by power and volume- insert usb flash drive formatted fat32 and the last firmware on it from 11.11.2020 PKG format...and most important the usb flash drive must be with MBR mode) try it many time dont give up..
2- bad sector on NAND ( Freez it to bypass the loop ) or bad BGA if some one work on it.

Diah, thanks for advice, take a look at screenshots and see if I done it right. Also, there 3 USB ports, any of these is OK?
On #2, yes, it could be hardware problem too. The main board was not abused and I was the first one who removed heatsink, but few screws are missing, so somebody already looked at it.

[Diah]

Re: Sony KD-55X750F bricked, keeps rebooting

i use always command at windows CMD if i have new usb flash to convert it to MBR,

look here i wrote before how to

[Davi.p]

Re: Sony KD-55X750F bricked, keeps rebooting

TVs have always a serial port for debug, if you have schematics it's better so you can check if it is present on vga or hdmi port, but if not there is at least a not populated connector on the mb of 4 pins.

[alfatv]

Re: Sony KD-55X750F bricked, keeps rebooting

I have a little bit of update.
Attempting update via USB didn't help, tried many times. I did format it as Diah suggested.
During boot-up the animation actually appears 2 times. After 1st attempt, the screen goes dark, then animation restarts again, but with brighter backlight.
Sometimes animation doesn't go through the process described above and stops in the middle, not always at the same point, but rebooting continues.
And couple of times the animation got stuck completely, had to unplug TV to restart it.

[Diah]

Re: Sony KD-55X750F bricked, keeps rebooting

you have much likely having drooping /unstable voltage feed to mainboards. need to take look and run the PSU as stand alone to check all output voltage include BL section.

[alfatv]

Re: Sony KD-55X750F bricked, keeps rebooting

you have much likely having drooping /unstable voltage feed to mainboards. need to take look and run the PSU as stand alone to check all output voltage include BL section.

Yes, it's possible. I did check voltages with multimeter during the process and there was no much fluctuation. Also there are few regulators on mainboard for CPU and memories, they looked stable too.
Backlight brightness correlates with DIM signal from mainboard, so it seems to be OK. And BL_ERR stays close to zero, so there is no backlight error.
I will try to check voltages with a scope.

[Davi.p]

Re: Sony KD-55X750F bricked, keeps rebooting

better to consult the log..

[alfatv]

Re: Sony KD-55X750F bricked, keeps rebooting

better to consult the log..

Still need to identify that port.
Take a look at pictures, is it RS-232C remote?

[Davi.p]

Re: Sony KD-55X750F bricked, keeps rebooting

I've never done it on a Sony, maybe it is that connector but you have to check if prior it there is a level shifter IC like max232 or similar, to know the correct interface, or them are those 4 pins on the bottom of board right to that quartz and under the optical out, the pins to be used are the one visibly at gnd and the 2 center ones, that is a 3v serial

[Diah]

Re: Sony KD-55X750F bricked, keeps rebooting

Still need to identify that port.
Take a look at pictures, is it RS-232C remote?

its so limited the UART, i am not sure you will get info to located the issue
however what i know and use
RS-232C are the TX RX for UART , the connection with audio stereo Jack as following

stereo Jack:
TIP = TV TX go to yours TTL RX adapter
RING = TV RX go to yours TTL TX adapter
SLEEVE = GND

Terminal Protocol:
Baud Rate: 9600 bps
Character Length: 8 bits
Parity: N/A
Start Bit: 1 bit
Stop Bit: 1 bit
Flow Control: N/A