Sorry I couldn't help further!
During the process of talking to you, I pulled an old non-working rev 5 board to use as a reference. I ended up tinkering with it and *almost* fixing it. Mine too had a blank screen. It had a broken Agnus socket, so I replaced that, but still blank screen. Reseating the CPU fixed that (actually I replaced it and then found it still worked when I put the old one back in), then I had a green screen, which means bad memory. I found that by pressing down on the RAM area, it would boot and give me the Insert Workbench Disk icon! So I carefully pressed down on each RAM chip and turned it on, and when I found the one that made the green screen go away, I put in a socket and replaced the bad RAM chip. I haven't been able to get rid of the green screen since! This board had clearly been worked on and given up by the last guy too, because the power pin (or was it ground?) had been cut on every RAM chip and then resoldered. I'm betting there's one that not making good contact, but I'd need 16 41256 chips to replace them all, and I don't have them. So this one goes back in the junk pile too!
so I give up, I will keep it as spare parts.