Two versions of this printer were sold by Digital Group in the early years, known only as the 'A' or the 'B' printers, they represent the bulk of all printers sold by the company. In later years, a Centronics 779-1 was introduced, but by this time the company was in trouble and it is unknown how many were ever delivered.

The printer is a 7-pin dot matrix printer that was manufactured by Practical Automation of Shelton Connecticut for the Digital Group. This 96 column printer advertised a speed of 120 cps, and a software based character set. Which meant that you could define your own characters: double wide, bold, etc. Although this was billed as a plus, it basically meant that the printer was "dumb"; it had no built in data processing ability. Your main processor did all the dirty work: timing, paper advance, printhead operations, etc.

One problem with this approach is the possibility of a software bug instructing the paper advance solenoid to engage while the printhead pins are extended... ouch. Hence the introduction of the "B" controller. :)

This printer could also print up to four copies simultaneously, on standard size letter or form feed paper, making it immediately useful for business applications. Along with software available from the Digital Group, this became one of the first hobbyist computers to make the transition to business computing, where the big money was thought to be.

One other failing of this printer if used with the factory cabinet, was the wholly impractical requirement to remove the cover in order to add paper--and only half a roll would fit! Almost immediately, after-market kits were available to place the paper roll external to the printer.

I searched for one of these for a very long time before Bruce Damer of The Digibarn offered me his--knowing it would be carefully restored. Just as I was completing restoration of the mechanism, I was able to find TWO more of them! When it rains... Anyway, the other two I picked up were in just awful condition. I cannibalized a few parts from them to make the Digibarn printer complete. The comments and photos on this page detail the restoration of the Digibarn printer.
  

I removed the printer from the non-original cabinet and began the disassembly process, photographing it each step of the way, as at the time I had no documentation to refer back to for reassembly. I also decided to log my time in the project carefully, just because I wanted to know how long a DG printer restoration would really take! Results? The progress on printer mechanism alone, shown here in these pictures took just over 95 hours--I did not time the interface board or cabinet restoration. It was a real pain keeping track of the time, and I gave up after the mechanism was complete. You get the idea though--my kids miss me.

The print head was in pretty bad shape. The pins had all rusted in place, and required great effort to remove, breaking a pin on one hammer in the process. The repair was difficult. Finding practical repair materials, settling on a technique, and doing the repair successfully on the first try, actually required a couple dozen hours of planning and setup. This was the most challenging part of the repair.

The next most difficult part was the rubber rollers. I picked up a half-dozen junk printers from a second-hand shop and reduced them to a pile of parts. Fishing through the pile, I pulled a set of rollers that had the same shaft size, but were too large otherwise. The oversized replacement rollers were re-sized by putting the roller shaft in a drill, and then running the drill in a jig over a belt sander. It took longer to set up the jig than to do the work, but the result were better than I had hoped--I'd call it a perfect repair! (I now have a lathe for such things--should I ever need to repeat this in the future. :)

The Before Photos

Reassembly

Final Assembly