The TRS-80 Revival, Part II

If you are coming into the middle, please feel free to check out Part I.

As mentioned in the previous installment, I had a TRS-80 Model III when I was young. I somehow managed to hang onto a Ziploc bag of floppies over all these years. Floppy disks were never intended to last for 40 years, so my mission was to try to image these disks, to preserve the data.

Back on my childhood Model III, I attached all sorts of floppy drives -- anything I could get my hands on -- to add storage. The original Tandy drives were 40-track/single-sided/double-density, but I had a 40-track/double-sided/double-density, and (I'll abbreviate here) some 80-track/DS/DD, along with some 35-track/SS/SD drives. I labeled some of the floppies with the type of drive, but not all. Sorting them out would be fun. Today, the highest capacity 5.25" drive that I currently have is a 40-track/DS/DD drive (known in the PC world as a 360K drive) so I currently cannot read any of my old 80-track disks.

December 29, 2022

The labeling on this disk seemed to indicate that my boot drive was 40/DS/DD, so it looked like I needed to use the PC 360K drive to read quite a few disks. It also looked like my handwriting hadn't changed much since the late 1980s. I connected it up, configured its jumper settings, and had a go.

I worked and worked on that 360K PC drive, attempting to make it function, to no avail. I finally removed it and put it on the bench, so I could drive its control signals manually and watch its reaction. I could never get the drive's head to engage when in the computer – I initially thought I had the jumper settings wrong, but I ruled that out by experimentation. On the bench, though, I made a discovery: I had an inkling that the index hole detection pulse had something to do with the drive making itself ready, so I was checking the output of the sensor with my scope. As soon as I touched my scope to the board, the drive would engage the head, and remain ready until the disk was ejected. After more poking, I found out that it was the pressure of my scope probe on the board that was making it work – pressing with a finger had the same effect.

Armed with this knowledge, I plugged the drive back into the computer, inserted the double-sided disk pictured above, and ... PRESTO! It booted! I suspected a bad solder joint, so I decided to remove the board from the drive and resolder every connection in that area. After reassembly, the drive worked again!

I spent several days browsing the contents of this digital time capsule from the 80s, enjoying (and occasionally cringing at) the contents of those disks, before finally attaching the drive to my Greaseweazle and saving images of the contents of the disks.

Please stay tuned for Part III, where I will cover the modifications and repairs that I made to this TRS-80.