@acn128 On some modems, it sets the line speed to 300.

I’m only guessing with the rest of this, so take it with a grain of salt. It’s possible you need to get an older modem, because that one may not have the ability to do 300 baud. If AT&N0 works (for automatically select), your modem probably can’t do 300, but if that also gives an error, maybe your modem has some other way to set the line speed.

@acn128 hoo boy, then all my bets are off! 😆

i was going to ask if it was an auto-answering modem, and if auto-answer was on, but with a selfmade modem it's all up in the air.

i'll be curious to hear what the solution turned out to be. part of that might be turning on the modem speakers and listening to see how/if they're handshaking and where it fails