Panasonic TX-L47ETW5 does not start after standby

A friendly hello to everyone,

we have a technical problem with our Panasonic LCD TV and need your help.

I've read a number of helpful posts on the Internet and here in the forum, but unfortunately I couldn't find a comparable post.

The error only appeared occasionally a few weeks ago, now with almost every switch-on from standby (red LED on).

The device is connected to the mains via a switchable socket strip. If it is now switched off and disconnected from the mains via the power strip for a few hours, the device only occasionally starts correctly from standby.

Normal behavior after switching on the power strip:

- green LED flashes for approx. 5 seconds, the backlight comes on, the green LED lights up continuously and after 5 seconds there is picture/sound.

or:

- The red LED LED lights up and the device can be started from standby using the power button on the remote control or on the device itself.

The device then runs for several hours without any problems.

Error:

TV is switched off via the remote control in standby (red LED lights up, power strip remains on).

If the device is now switched on again via the remote control or the switch on the side of the TV, the green LED flashes for approx. 5 seconds.

the backlight does not come on (green LED lights up continuously) and after another 5 seconds no picture/sound either. The green LED lights up continues permanently as in normal operation.

This error occurs regardless of whether, for example, other devices are connected.

The following parts are installed in the TV:

- Panel: LG LC470EUD (SE)(FE)

- LCD driver: LG KLS-E470DRGHF12 B Rev 0.2

- PSU: TNP A5608 2P TXN/P10TWUB

- Motherboard: TNP H0993 1A TXN/A10TYUE

- T-Con: TNP A5587 1FR

Previous troubleshooting and findings:

- Operating hours according to the service menu approx. 17,000 with 14,000 on/off operations

- Software update via SD card not possible, since the current 1.269 is installed

- Checked all circuit boards with a microscope for cold solder joints or abnormal components, no abnormalities found

- no reaction to cold spray or heat on all boards in working condition as well as with error

- Various service manuals for similar devices were unfortunately not helpful, especially since the LG components were also missing

- Self-Check does not bring any errors, but can only be started if the backlight and image are also active

- LVDS cable to T-Con disconnected: error still occurs

- no blink codes (red LED)

further considerations:

- I did not want to heat (reflow) the IC8000 BGA for the time being on suspicion, since replacement mainboards are currently available

- I don't want to remove the panel on suspicion to check the individual LEDs

- I haven't found a way to reinstall the software yet

What could that be?

Thanks in advance for any tip!

Greetings Marc