Oh well, the monitors now broken so that doesn't help.

Also discovered the cmos AA batteries had rotted, and on their removal and replacement with new battries the machine no longer gives the friendly 'boop' as riscos starts.

According to the RISC OS 3 manual, resetting the CMOS by pressing "R" or "Delete" during a power-on sets the WIMP screen mode to 12 (640 x 256 pixels at 16 colours), the display sync type to composite (important for TV set compatibility, as I understand it) and the monitor type to 0 (old-style RGB monitors and TV sets). So if your CMOS RAM manages to keep those settings, they should be OK for you.

When I tried to connect my A3010 to a 100Hz CRT TV set, I found out that in order to actually get a picture on the screen, I had to tell the TV set to use the _RGB signals_ of the SCART cable, not YUV, "composite video" or whatever the other - inferior - standard is called.

The RGB->SCART cable I used had been built according to the diagram in the A3010 welcome guide.

You say it doesnt do anything at all now, don't worry. I opened my A5000 up and did something and thought that it had died. All you need to do to fix it is to give the mainboard a good clean and all should be well. Also push down on the ROM chips to make sure they are firmly in place.