exxos's Atari, Amiga & retro forum

OK. It's the power supply. I lose the -12V. Probably a capacitor.

The -12V is not used anywhere else on the board, which is why I wouldn't see any other issues. I can look at this in the next couple of days. I have tomorrow off for a start.

PSU fully recapped.

The +12V is still running high, at 13.13, but that's half a volt down on what it used to be. +5V is 4.96 and -12V is just over -12V.

Let's see if the -12V line keeps running.

After more than an hour it seems stable, so I think that I've found the issue.

Now to wait for the floppy controller PCBs to arrive.

Yep. Fixed. The machine's been sitting there all afternoon and the serial port is fine.

Ah, damn those -12v lines!!

Glad to hear you're making progress with this machine, it's good to see something that battered and bruised returning to life.

The new PCBs have arrived and I have the day off work, so I can look into building one this afternoon and seeing if I can get the system to use "normal" floppy drives. If this is the case then this is a definite move forward.


I've been thinking about how best to proceed with the least hacking of the original machine and I think what I may do is fit an external floppy IDC socket using masses of hot glue to the side of the original connector on the motherboard. This corresponds to one of the case openings for expansions. In this way (assuming that I can get normal floppy drives working) I can then plug in a set of external 3.5" drives originally meant for the BBC Micro or Sinclair QL. This would leave the original machine with the original drive disconnected but two external drives instead. Not as neat but far more flexible.

Assuming that this all works out I can start thinking about designing a memory expansion card with possibly a hard disk emulation as I've found the description (though not the schematic, though it is referenced) of the original 10MB MFM drive controller board.

I'm going to need a bodge wire! KiCAD/Freerouting didn't connect pin 24 of the socket (clock) to anywhere for some reason, even though it all labelled on the schematic correctly.

Never mind, eh?

OK, it doesn't work.

Well, the circuit does the clock division correctly but the floppy controller isn't reading at 250bps. If I change the jumper back to the 600rpm setting and change the Gotek setting too then it works as before.

I wonder if I have to pull pin 17 low as well.

OK, found the KiCAD problem. The label was misplaced slightly so it wasn't actually connected to the "wire". Anyway, I think I'll have to try another bodge wire from pin 17 (8-/5) on the socket to pin 20 (GND).

We have a winner, at least on the RPM side of things. I'm just running the diagnostic tests now but it looks good.

Once this is working I can try the /READY /DSKCHG hack to see if that's working.

P.S. Oh, it's reporting that it can't write properly. :-/
P.P.S. Formatting and file copying seems OK though.
P.P.P.S. Using a real floppy drive and an Apricot floppy which I know should give a boot error '99' as it's from the wrong machine and it does read correctly and give that error, so it looks good.