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