I've been casually following the action here and finally this has spurred me on to take another look at my board set which was left, sick and fevered, on my workbench sometime around Wed Aug 13, 2014. I'd made a stupid mistake when building the board and omitted two vital resistors (D+/- pull-ups on the usb IIRC) which resulted in the FX2 being invisible. This led to some serious, and unnecessary, rework - and the eventual lifting of a couple of pads at the FPGA. I was a little ... impatient.
Anyway I'm a lot^k^k^k bit more patient now and having had a lot of practice with ultrafine tqpf and the reworking thereof I decided to have another look at the board. I cleaned up some solder joints, repaired the lifted traces and, following Chris' excellent advice about testing the mechanical linkage 'twixt pin and pad, I set about with a needle and microscope. I found an open joint on the FX2 and a well hidden bridge on the FPGA.
The early board tests all passed and I could checksum the content of the chips. Success! The board was only 3/4 populated though - I was testing as I built - and of course I couldn't find the last remaining parts. Farnell have come through and now that the EEPROMs are in place I'm pleased to announce that - pending a test in the old MD - I appear to have a fully working board set!
I have 3 PAL MDs, a region modded MK1 and 2 MK2s. I don't know what revision these are but I'm happy to rip them open to find out. I have to admit that my megadrive ambitions are, at this point, vague to non-existent but I will be more than happy to execute tests or experiments and hopefully add to the knowledge pool.
If I can get my head around this system then I'd like to use it as a Z80/6502 ICE.
Glad to be back,