On the Poke3:
EDL cables don't work.
There is no button-ism to force it to EDL or fastboot.
There is that recovery button-ism, but timing is difficult (at least for me).
If you open up your device there are easy possibilities:
The EDL test points are right there and you just need to short them and long power press.
The 1.8V UART interface is there. It responds to more than 50 rubout (0x7f) characters in the right timing.
Fortunately the timing can be detected by the logging coming from the abl.
I've even a little program for that.
Code:
C:\>abltest com3
Listening...
Starting
Jabbering...
Detecting...
Going to EDL mode!
Done
Of course on my Poke3 I have installed a magnetic reed switch so that I can activate EDL mode by an external magnet.
The UART also has a connector so I can plug in without removing the back.
I hate removing backs.
My suggestion: Remove the back.