Are these GEN1 or GEN2 M4NGA ROMs? Just wondering which FreHD patched U70 (C) ROM I should try with this "standard" set. It's going to take me a little while to try these since I now realize I'm out of 2764 EPROM's in the parts box, but did find some cheap(ish) MCM68766 online, so I think I'm just going to try those since they don't require an adapter board to fit in the stock DIP24 U68 spot.
Those are GEN1 ROMs.
Also, I did trying booting without the RS-232 board attached with the various U70 ROM's and it didn't seem to make a difference.
Good to know the RS-232 is not a factor. I looked at a boot trace in the emulator until the patched ROM tries to load from the FreHD and there's just nothing unusual I can see. In fact, it does very little except some trivial initialization and a clear screen before it attempts the FreHD boot. There is one interrupt that occurs during the screen clear but that's it. And I otherwise cannot see how the patch would make any difference whatsoever.
It is really quite baffling. I can only think of two possible things to try at this point. One would be to make some kind of partial patch to the U70 ROM to figure out what exactly makes things go wrong. The other is to start the student station with the stock ROM set and then do some BASIC commands to load the FreHD boot block and see how that goes.
In the spirit of looking where it is easiest, here is a sequence of BASIC commands that should boot the FreHD.
POKE16912,16 OUT197,4:?INP(196):REM Should show 254 if FreHD attached FORI=0TO255:POKE20480+I,INP(196):NEXT POKE16526,0:POKE16527,80:A=USR(0)
Type in the commands in direct mode; don't put them into a program to run. I'm not sure that they'll work more than once and if something goes haywire after one of the statements we'll want to know that.
If that returns to the READY prompt then the FreHD boot block couldn't load FREHD.ROM. If it fails then trying again with all but the last line and then PEEK()ing at the 256 bytes loaded may provide some insight.
This won't tell us anything about the ROM patch problems, but it will show that the FreHD can work with a Student Station.
Edit: Fixed bugs. Initial poke was 32, should have been 16. And it is A=USR0() was wrong.