exxos's Atari, Amiga & retro forum

Awesome! Thanks :)
It's one of those downloads I've had for years, but isn't of much help when it's deeply buried along with hundreds of other files.

Well, I've solved the "Modem 2" and "Serial 2" port problems. Like many of the other MSTE problems I've had this was a frustrating/silly but cheap fix. I pulled out (thanks to a PLCC extractor tool which I've had much use for) the Z85C30 (a PLCC chip underneath the power supply) and this is what I found: Once the pins in the upper right hand corner (and other pins close to each other) were straightened out it worked a whole lot better! Using ConNect and selecting the appropriate ports I could now communicate with my STe on all three of those serial ports :D
So to answer my own question: U306 (MC68901) appears to control "Modem 1" while UA04 (Z85C30) appears to control "Modem 2" and "Serial 2".

I also gave the diagnostic cartridge a go, but the remote display still only worked with "Modem 1", so I guess that's the way it goes.
The SCC and serial tests still didn't work, so I assume there's a separate SCC loopback connector to be used -not the serial loopback connector I made. Does anyone have a pinout for it?

Yes, there’s a loop back plug. Don’t know of anything that uses that serial port.

Pacman wrote: 09 May 2021 10:14 I also gave the diagnostic cartridge a go, but the remote display still only worked with "Modem 1", so I guess that's the way it goes.

The diag software will only output to the 68901 serial port. As you say, that is the way it goes. :)

Thanks for confirming as I couldn't find this info in the Mega STe service manual.

Perhaps this info could be added to the "Basic Troubleshooting - Diagnostic Cartridge basics" sticky?
That, and the fact that you can control the menu (i.e. select tests from the menu etc.) from the other computer that's connected via the nullmodem cable.
And finally, that it also works with other computers and not just PCs (for instance another (working) ST).

Can I now safely assume that since the two SCC controlled serial ports ("Modem 2" and "Serial 2") are OK since I'm able to communicate across the two computers (MSTE and STe using the Exxos nullmodem cable and Connect95 where I can see what's being typed on the opposite computer), or would I need a suitable loopback plug to verify this?

If you can control the tests via a second computer then serial must be working .

Ah! Yes, I remember being surprised that I could do that from my STe.
But the diagnostic cartridge serial output is apparently only designed to work with "Modem 1", so I'm unable to check the other two that way.