This is as far as I got into the steps you suggested:
1. Disconnect the power cable.
2. Hold down "On/Off" button.
3. Reconnect the power cable.
4...
Holding power and pressing cancel once lights up an orange led next to a lightning symbol, and not much else.
Pressing cancel twice gives "Factory Mode 1", which runs a few rollers, but doesn't say Idle after a good minute or so, and doesn't seem to repond to anything.
Pressing cancel THREE times switches on "Factory Mode 2", which gives the following options:
SCAN AGING
Asks how many times, options 1 5 10 15 20 endless
Tried 1, seems to run the scanner along once and says complete.
?
SELF CH
Pressing OK gives the following:
OK R134-231
G137-237 B139-236
PNL CH
Fills all blocks of the LCD screen to test
FB READ
Options for BK/CL, Normal/Silent, and DPI settings, seems to test scanner again
ADF READ
Same options as above, doesn't seem to do much
FAX CH
I can't even be bothered with this, I don't use the fax
G3 TX
Shows G3 TX and 4.8k or somesuch, modem speaker blares static
G3 V.17 TX
Makes more silly nostalgic 90's dialup modem noises.
G3 V.34 TX
If this is testing the modem, I can't be bothered again
TONAL TX
Lets you test speaker tones at 462Hz, 1100Hz, 1300, 1650, 1850, 2200 Hz, loadsa fun :D
RELAY ONOFF
Lets you switch on/off some kind of internal switches named CML and H, not playing with this.
LINE DETECT
Press right it says CI=0, HOOK=1, press left it says CNG=0 HOOK=1, something to do with phone again, so stuff it
DTMF TX
Says DTMF Tx on screen... ?
SPEAKER CH :D
Again lets you run through various frequencies, this time with a volume control that only goes UP. Clearly great for pissing neighbours off.
CIS RUN
Repeatedly tests the scanner at the short end.
Out of options for Factory Mode 2
Pressing cancel 4 times runs the printer as normal.
5 times moves some rollers and bits but shows nothing on-screen.
6 seems to run as normal again.
Not pressing the cancel button at all does nothing.