Okay, I know this is a total long shot, but here goes:
I'm trying to get an old HP LaserJet IIIp to work with my Mystic Color Classic, i.e. with a regular older Mac.
The IIIp is a non-Appletalk printer with parallel and DB25 serial ports. It is confirmed in good working order.
The Mystic is running OS 8.1 and is also in good working order.
Here's what I've tried:
Following http://macfaq.org/hardware/network.shtml#Q2.7.3 I have downloaded and installed Chuck's Printer Driver. I have attached three different Mac serial-to-DB25 cables between my Mystic and the LaserJet.
One is an Imagewriter I cable (Apple logo'd). The DB25 end has six active pins.
One is an HP cable. The DB25 end has five active pins, in a different pattern than the Imagewriter I cable.
One is a generic cable. It might be a high-speed modem cable; I'm not sure. In any event, its DB25 end has all 25 pins.
None of these works. I've tried each on the modem and printer ports. I get a "PrinterError: Port in Use" message all the time. I have set Appletalk to a different port (ethernet), and I have also turned Appletalk off completely. I still get the error.