The writer pinpoints the major problem that I had with using the ROM earlier, which was that the beeper is not fully implemented for MAME. They describe how to get to the setup screen and change it to "flash" instead of beep.
Note that because the specialist keys ([ctrl] for "use front" and [alt] for "leap") can conflict with browser shortcuts, it's probably preferable to try in the standalone emulator instead of the online one.
(author) Thanks! Yeah, it annoyed me how it kept freezing until I noticed it was always during an error state, and from there it was a quick trip to narrowing it down to the beeper. I think this is part of the DUART emulation and that is acknowledged to be incomplete still.
Note that because the specialist keys ([ctrl] for "use front" and [alt] for "leap") can conflict with browser shortcuts, it's probably preferable to try in the standalone emulator instead of the online one.