Last time we powered on the SFD 1001 floppy drive and discovered that it didn’t work.
At least it did work a little bit – the drive and power LEDs came on. But that was it. In this video we go through the process of fault finding to discover what the problems are and (hopefully) fix them. Even if it does seem at times that we take one step forward and two steps back.
We know for example that the CPUs (yes, there are two of them) and VIA are common with a 1541. So we can easily swap these chips over and see if they’re working. Some of the other chips are harder to check, since we don’t have spares or another machine to try them in. We’ll have to rely on other techniques, examine signals on the scope, check voltages with the multimeter.
And once the motherboard is running, we can try formatting a disk.
This has to be the first step, because this drive is not compatible with the 1541, so it can’t read 1541 disks. Instead it’s compatible with the 8250 (which stores 1MB on a regular DSDD floppy). Sadly I don’t have any 8250 formatted disks, so if it doesn’t format, we’re in a bit of a jam.
(although as the video progresses I do manage to get hold of one pre-formatted disk)
Testing the drive will be done using the Tynemouth MiniPET (see https:/?p=46 ) This has an IEE-488 port so can talk directly to the drive (the serial bus used by the Vic-20, C64 and later computers, was derived from the IEEE bus, although it’s not compatible and of course, much slower). We can also directly use the Basic 4 disk commands:
DIRECTORY
CATALOG
HEADER
DLOAD
DSAVE
? DS$
etc
which again the C64 didn’t have (although they were reinstated for the Plus/4 and C128).
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