The system came with a box of what looked to be well-worn disks. I had found no other disks online so as far as i knew, these disks, or copies of them, were the only disks that would boot up this machine.
I have one boot disk and a few data disks. They also seem to work in the machine.
I cleaned up the drives, and they seemed to work ok except for one quirk: they will only read data disks from the drive that is used to boot the machine. I’ll have to think about what that means – perhaps an addressing issue – or perhaps there’s a command required to change the current drive.
I’m pretty sure I’ve tried both drives with both controllers and with both controllers as drive 1. It’s another mystery, but I can’t mess with the disks too much until they are copied.
As far as I can tell, the machine makes no provision for copying disks. A bit of an oversight, I think. Surely there is, but without a keyboard I have no way of exploring anyway.
The disk drives are Shugart SA-400 units. They are single sided and have only 35 tracks. We’re peering back to a 1976 design here.
As I understand it from the manuals, they are single density disks (which turned out to be wrong) with 10 sectors per track. Unfortunately, single density really means that the coding is different. FM instead of MFM used for double density. The drives don’t care about the coding – the decoding is done on the floppy disk controller.
The disk controller cards use western digital FD1791B disk formatter/controller ICs, which is a fairly common family. Between the industry popularity of the shugarts, and the western digital disk controllers, i expected the formats to have a lot in common with other formats. I was dreaming.
There is a reasonable chance that ImageDisk could read the disks on an IBM machine if I was using a disk controller that supports single density. I don’t have one. It’s worth pursuing though because some other old machines also use FM anyway.
I purchased a relatively cheap Goldstar Prime 3b card which was rumoured to support FM, but i had no success with the card and Imagedisk.
Next was an Adaptec SCSI card which is also a floppy drive controller and is known to support FM. Fail. I tried another Adaptec card well known for supporting single density: Adaptec AHA-1542B. Fail. I concluded that it wasn’t FM coded.
I thought perhaps it might use some other variation. The Lexiton floppy disk cards are, after all, custom cards.
That really left me with very few options. Perhaps some custom hardware that might do the job – a catweazle card or a kyroflux – but they are hard to come by, expensive, and there was no guarantee of success. Either greaseweazle (and fluxengine) was not available in 2018 or it had escaped my attention. I put the job on hold.
My floppy disk skills have come a long way since 2018. These are double density disks but with a unique coding. The coding is built into the floppy disk controller cards. The disks can be read and written with greasweazle, but they cannot (at present) be decoded into recognizable sectors.
In early 2019, i noticed an isa card on a popular auction site, with a vague description, that was called a copy card. Being priced moderately, being located in Australia, and noting that it had what looked like a floppy disk edge connector, I thought it was worth making an enquiry. The seller was kind enough to send me some scanned pages from the manual, and it did sound remarkably like it could do a low level floppy disk copy. It sounded like it may have been a clone of the old CopyIIPC hardware.
It works by taking over the floppy drive data signal. The floppy drive cable is routed from the controller to the copy card and then on to the drives. It has quite a good little manual (no doubt inspired by the original) and the copy program has a few options to play with. It’s really made for copying tricky games disks but claimed to also be able to copy other formats such as apple and Atari. The irony of a copy card and its software being cloned was not lost on me.
I popped it into my PC XT. Initially i had no success with the lexitron disks, but I tried an apple ii disk and although it wouldn’t boot it did give a catalogue listing back on the Lingo Apple II clone which was encouraging.
I tried all the options, and found that with track length matching, and weak sectors turned on, I could get a Lexitron disk that would sometimes boot. I made a few more attempts and got some disks that seemed to boot every time. That doesn’t mean that they’re error free, but at least I could work on the Lexitron without putting further wear on that original disk.