[vcf-midatlantic] Documation card reader fix
mloewen at cpumagic.scol.pa.us
Wed Aug 10 20:10:36 EDT 2016
Those of you who own/have used the Documation tabletop card readers
know that they have a problem reading cards that have a diagonal cut on
the upper right-hand corner. On many (but not all) of those cards, enough
light spills over to the 12-row photocell that it thinks there is a punch
in column 81, and the unit throws a READ CHECK.
Carl Claunch has come up with a hack for the Control Card to work
around the problem. I modified my M1000-L yesterday, and it now handles
the problematic cards without error. As I mentioned on Facebook, "It
ain't pretty, but it works."
Al Kossow has made the modification documents available on Bitsavers:
I used Carl's daughterboard circuit, but replaced the 7433 quad-NOR
(open-collector) and pullup resistor with a 7402 quad-NOR. I had
initially tried Stan's simpler version, but didn't realize there was a
trace underneath D8 connecting pins 2 and 13 and the mod didn't work.
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
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