Quote Originally Posted by KC2UGV View Post
Ok, update! Leaving it off for a few hours + another rest (The manual details a "jumper" CPU reset seemed to clear it up). So, it's working FB now :) Seems like I know what happened. I think the serial port for this machine has a really, really low "off" state (12V). This biased the transistor, I think, and sent the wrong polarity to the PTT of the thing.. At least, I think that's what happened.
Most of the later generation solid-state rigs I've dealt with keep their PTT lines about 1kohm or so above ground when keyed. You might want to look into using an optoisolator (4N25 or equivalent) as a "buffer" between the two devices.