A black screen means a cpu problem; so it's entirely possible you're suffering from the dreaded cold solder problem. It could be just about anywhere; but a quick examination of the cpu socket and crystal oscillator may help. It could also be one of the ttl chips or a pal somewhere on the board. You could also try reseating the cpu chip and the small square custom logic chip on the accelerator board (it should be an AMD chip); you'll need a small jewelers tool and a PLCC chip extraction tool (Radio Shack has them). If all else fails, JJ Boulet at Amiga Center fixed an old 68040 GVP Combo for me. It had bad solder joints under the 68040, he replaced the PLCC chip holder for that big custom chip (mine was cracked/warped) and he also replaced a couple small buffer chips for me...works now.
