Diehl Combitron (Was: "Oddball"(LGP-30)

[dwight elvey]

>From: "Rick Bensene" <rickb at bensene.com>
>
>
>Re: Getting Microcode off of Tape and Into Microcode Delay Line of Diehl
>Combitron Calculator
>
---snip---
>
>These machines were notorious for not "booting up" properly at power up
>time.  The tape would read, but the code that got loaded was incorrect,
>resulting in a calculator that was catatonic, or sometimes did weird
>things.  The main cause of this was contaminants getting in the tape
>reader optics.  The tape reader was optical, with a light source on one
>side of the tape, and two photodiodes on the other side.  As mentioned,
>the tape had two tracks, one a clock track, and the other a data track.
>If dirt or dust, or oil from the mechanical printing mechanism got into
>the optics, it would cause mis-reads, either clock pulses would get
>missed (meaning missed bits in the microcode), or data bits would not be
>read properly, again resulting in a bad microcode load.  Keeping the
>optics clean was a main maintenance point for these machines, along with
>proper lubrication of the very mechanical print mechanism.

Hi
I found that the one I had would fail to boot for another reason.
Even cleanning the optics wasn't totally enough. I found that the metal
tape would not always pass smoothly through the reader. Some
times it would stick a little and then flash through the reader, faster
or slower then intended.
I found that I had to clean the surface of the metal tape as well
from any stray grease or corrosion.
I'd truly love to have one today. I'm sure the one I used is long gone.
Keep up the good work. Many of the early electronic calculators were
truly great computing machines.
Dwight

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