some updates to this torrid tale.
I've bought a pre built willem programmer, which is working well (as far as I can tell ). I've flashed and verified nearly all the A7v600 roms that I can find with no success - still the same mystery beep code. 1 second on 1 second off.
I'm torn between throwing this board out and persevering. Boards with SATA, 5 PCI slots and digital audio coax out are pricey and hard to find in UK.
But... if Willem is flashing correctly, then maybe the problem is terminal and perhaps I should just give up..
I've been considering buying a pci test card, so I could read at what address the bios is failing at, does that seem like a sensible idea?
edit: another thought, maybe I should find a PCI vga card and check the problem isn't with the AGP bus. but I suppose the test card should tell me this..