I have a rom 3 IIGS that came with a rev 3 scsi card. I find the card to be extremely unstable. Without the card, my IIGS runs just fine, but with the card, (which i use for booting GS/OS off a scsi zip card) the card is extremel unstable. About 80 to 85% of the time that I power up the machine with the rev c scsi card in there, it boots and crashes to the monitor. It'll do this whether or not i'm using the micronics scsi drive it came with or my zip drive. It'll even do this when nothing is plugged into the scsi. Once in a while, it'll boot right into GS/OS, but it's pretty rare. I've even checked the sole electrolytic capacitor on the card and it checks out fine.
I thought the problem was the SCSI termination power so I did the diode mod, but nothing changed. The card sits in slot 7 and the config is set to 'your card' for slot 7 as well. I have replaced my power supply with what is known to be good and verified the voltages coming out of them when the machine is powered on.
This has been driving me crazy forever, I could use some help!