As promised I’ve taken some close-up pictures of the programmer PCB. The chip is a MAX662A and the capacitors are connected to it as per the datasheet. I’m afraid that these aren’t great quality pics because I couldn’t get the light right, I will get some better ones and upload them in due course.
I’ve not done anything to try and work out a schematic or pins assignments as yet. However I am pretty sure that I was barking up the wrong tree with pin 1 on the serial connector. Whilst it does have 12V applied to it via the output from the 662 I don’t think that this is needed for the flasher to work.
I’ve had a useful discussion with someone who makes these cables up and it appears that the key thing you need to make them work is the FTDI chipset on the serial controller – which is presumably what the official cable uses.
I’m going to have another go at flashing the firmware at the weekend so will post the results.