After you verify it works, you need to unplug it. Then open the case.
(1)Battery: is located to the left of the 8373 Denise IC. It's usually wrapped in green or blue plastic. Is it or the legs corroded. If corroded, this is your first problem. You will want to remove this battery, and attach leads to extend it away from the motherboard by placing the battery in a plastic medicine bottle.
(2) Remove all cards, daughterboard, drives, drive bays. You need to get down to the motherboard under the power supply. You want to write-down all the chips and their revisions. (The WD33C93C-04 is common, you'll need an -08). Others chips to note are the ROM 0, ROM 1, DMAC, Buster, Ramsey. Also look at J351 to the left of Ramsey PLL. Is this a 16 or 25 Mhz unit. There is an oscillator can, a 25Mhz unit uses a 50 Mhz can. There's also jumper J151 and J152 to the left of ROM 1.
A lot has been said by others, but these questions actually are the basic questions you need to answer. These answers determine basis issues like compatibility with drive size, SCSI cards, and processor cards.
SCSI drives are not cheap like EIDE drives. It's nice to have that 40 gig drive, but what if your ROM version and AmigaOS do not support that drive?
