[vcf-midatlantic] Documation card reader fix

[Mike Loewen]

    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."

http://q7.neurotica.com/Oldtech/Documation/0809162259.jpg

    Al Kossow has made the modification documents available on Bitsavers:

http://bitsavers.trailing-edge.com/pdf/documation/documation_fix/

    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/