Defect circuit board in the charging station 220AC

[Hopptjohej]

Sorry for writing in English,
I'm trying to fix the circuit board in the charging station and need help locating the fault.
When connected with an unbroken loop cable, the LED flashes twice green (weak loop signal) even when I disconnected the loop cable the station blinkes twice.
I have replaced a burned 470ohms resistor the NPN (BPC55) transistor that sat next to it, but still no success.
Any tips on further troubleshooting, another component that usually gives up?
I have read this but I have an other failure [url http://automower-fans.les-forums.com/topic/7773/reparation-reussie-de-la-carte-d-une-station-d-acc/]
Thanks
[img https://ibb.co/WHNDJGg]
[img https://ibb.co/y80bPxX]
[url https://www.dropbox.com/s/rsr37ciuwyl9o9c/PXL_20210426_144200176.jpg?dl=0]
[url https://www.dropbox.com/s/ztr23bshe6g8j87/WIN_20210426_16_45_03_Pro.jpg?dl=0]

[Razmoket]

Hi
This board is a PITA to repair.
You need to check signals at the output. You should get short pulses of 50uS, 35V amplitude (less when loop is established)

Plenty of component can fail. There's a smalll shunt of a few tenth of ohm connected from ground to the emitter or collector of one power transistor, which is prone to fail. Otherwise, there is no easy fix.

[Hopptjohej]

(+)
Thanks, I'll give it a try.