30 Jun
2004
30 Jun
'04
1:28 p.m.
>> Not a silly fault, but a silly thing to do was
the time I
>> had a malfunctioning -15V regulator brick in the same
>> machine. I put that on an extender cable (this isn't an
>> offficial DEC thing, but I have a cable with an 8 pin
>> mate-n-lock plug on one end and a socket on the other for
>> working on such bricks). I was trying to figure out why it
>> was giving no output into a minimal load and very foolishly
>> I disabled the overcurrent trip. Alas the reason it was
>> giving no output was that the crowbar was firing. With no
>> overcurrent trip, the crowbar blew just about every
>> transistor on the PCB (and finally the fuse). The flash was
>> spectacular....
Late 1970's I was involved in the development of automatic test equipment
(PDP-8 based!).
The power supplys were programmable, but not accurately, so the standard
procedure was to have circuitry that would connect the power supply to a DVM
[direct BCD parallel interface, a real dog]. So you set the voltage to
nominal, beaure the error and adjust the voltage accordingly. Now lets see
what happens if you forget to connect the DVM....
Programmed Actual Error
5.0 0.0 -5.0
10.0 0.0 -10.0
20.0 0.0 -20.0
40.0 0.0 -40.0
57.6(max) 0.0 -57.6
Of course by this time the entire system let out all of the magic
smoke......
The result was that LARGE diodes were placed across the power supply leads
to protect the fixtures. They quickly got the moniker CYSH [Corbin You S***
Head] diodes.
David Corbin