Path: utzoo!utgpu!attcan!uunet!husc6!ukma!nrl-cmf!ames!amelia!prandtl.nas.nasa.gov!msf
From: msf@prandtl.nas.nasa.gov (Michael S. Fischbein)
Newsgroups: comp.misc
Subject: computer follies
Summary: Killer tty
Message-ID: <1065@amelia.nas.nasa.gov>
Date: 27 Sep 88 19:22:41 GMT
References: <5856@ihlpf.ATT.COM> <37600006@pyr1.cs.ucl.ac.uk>
Sender: news@amelia.nas.nasa.gov
Reply-To: msf@prandtl.nas.nasa.gov (Michael S. Fischbein)
Organization: NASA Langley Research Center
Lines: 36


   I worked designing microprocessor based fire and security
alarm systems for skyscrapers, back when microprocessors were a
brand new idea.  Well, we had development systems from two
vendors and only one terminal.  I came up with a cable to hook
the ASR-33 up to the other development system so we didn't have to wait
for that vendor to get a terminal to us.  I carefully checked the
connections, plugged the cable into the terminal and put a trusty VOM
on the connections to make sure the signals were right.

   OK. Both off, connect the ASR-33 to the computer.  Turn on the
computer.  Turn on the teletype. POP! Hissss... Yank both cords out
of the power strip.  Notice blue smoke coming out of the computer.
Go back and measure the signals on the data connector with
an O-scope.  Gee, there's a 40 volt AC square wave superimposed on the
TTL signal.....

   We tell the vendor of system 1 (that supplied the teletype) what's
wrong with the teletype and ask for a replacement.  No, that's the way
it is supposed to work.  Yep, sure it is.  That's OK, they'll install it
on their development system.

   They plug the teletype to their machine when it arrives.  POP!
Hisss...  They take it to their local distribution center, the
service engineer checks it out thoroughly, ``repairs'' it, hooks it up
to one of their systems.  POP! Hisss....  Two systems later, he admits
mystification and ships the killer teletype back to the factory in
California.  Last I heard, the teletype had vaporized three systems
back at the factory and they couldn't figure out what was wrong.

		mike

Michael Fischbein                 msf@prandtl.nas.nasa.gov
                                  ...!seismo!decuac!csmunix!icase!msf
These are my opinions and not necessarily official views of any
organization.