I tested both of my 3.5 Drive cards today, and both have issues:
I believe that Apple used an AMD EPROM and not a Mask ROM for these cards, as I can felel an erasure Window under the labels, so I suspect that bit rot has caused both to become unusable.
Here is what I see if I attempt to boot from a 3.5 Drive connected to one of the cards.
Occasionally I see `Check Startup Device` or `Failed to Load ProDOS`.
The break to monitor is the most common, and it occurs on attempting to scan the drive connected to the card.
The drive is a Superdrive, (Sony 75 mechanism) and is known to be good. The GS boots from it in the normal Drive port.
The second card causes the GS to halt, and the LED indicator on the GS mainboard dims.
Have any of you seen these symptoms and can anyone confirm if the AMD firmware ICs are indeed EPROMs? I didn't want to remove the labels from them.