Unable to flash firmware

[Hemulen]

I have a Geeetech A20T with the GT2560 v 4.0 board. I wanted to add the BLTouch to the system, but it appears that I cannot flash any new firmware to the printer. Over the USB I get Connection timeout, regardless of computer platform and software (Octoprint, Cura, Arduino IDE, etc. etc.).

Checked Internet many times, and got down to that it seems that the only remaining possibility is by programming directly over ICSP using an Arduino board as programmer. However...

It turns out that this GT2560 v4.0 board does NOT have any ICSP pinout at all (at least not that I could find). The fix, according to some, is to use the pin header for the SD-card reader... which on my board is strictly soldered in place.

So, I have run out of options, it seems. Do I have to replace the board to a newer version, with an ICSP connection, or is there any other way that I can flash the firmware..???

Please, anyone! Help!