Zero dB schrieb:
It it possible for the SSC to fail in such a way that transfers won't work, but the logic still does ? I can "session" into the card andget a responsive prompt, but can't transfer.
Sure. The 6551 may have failed, or the baud rate generation circuit. If you dropped the card, the crystal may have broken.
You can remove the 6551 from its socket and connect pin 10 to 12 with a jumper wire. Then start Hyperterminal on the other side and see if you get back what you're typing. If you see the remote echo, everything up to the UART chip is ok.
Testing the crystal requires an oscilloscope. However, for a quick test you can just connect a working part in parallel. Usually a broken crystal is broken in a way that it isn't present in the circuit at all anymore.
Patrick