[vcf-midatlantic] Scopewriter Issue Resolved.

Herb Johnson hjohnson at retrotechnology.info
Mon May 20 12:15:47 EDT 2019


> It’s interesting how many of the hobby designed products from the mod 70’s have marginal aspects to their designs.  Whenever anyone recreates or restores any old electronic device, it often can be a tricky problem to determine whether a problem is introduced or original to the design 
> 
> regards,
> Mike Willegal

The very earliest microcomputers or microprocessor-based things from the 
early to mid-1970's, were often designed by people new to 
microprocessors and/or TTL logic. Some of course (TV Typewriter)  were 
all TTL logic. The very earliest microprocessors needed odd voltages and 
timings. So some of the logic design was a bit, er, funky.

A common practice was to use a resistor/capacitor circuit (R/C circuit) 
to create timing delays, or turn level-shifts into pulses. These don't 
age well, and didn't work well when new. The IMSAI front panel has a 
couple of these. Also, "straight" TTL draws a lot of current; later 
LSTTL and much later ALSTTL draws less current and is faster. Early CMOS 
was challenging too.

Things got better, later on. And some brands (Compupro, etc.) produced 
pretty solid designs from the start. These are restorer's considerations 
which aren't documented. It's part of the fun, in my opinion.

Notably,
Herb Johnson

Herbert R. Johnson, New Jersey in the USA
http://www.retrotechnology.com OR .net
preserve, recover, restore 1970's computing
email: hjohnson AT retrotechnology DOT com
or try later herbjohnson AT retrotechnology DOT info


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