🚀 go-pugleaf

>Ok, another exploding computer story (true!)..

   A while ago I was trying to hook up an old Timex/Sinclair 1000 (ZX81 for
some) as a stepper motor controller. Well, while testing out the interface
logic (without the motors connected), I had bypassed the current-limiting
resistor for some reason. Of course, when I plugged in the motor itself,
I didn't remmber to remove the short.
   The logic lasted quite a while, considering. I'm not sure exactly what was
happening; "step" pulses from the computer would get confused somewhere and
would make the motor just wave back and forth erratically. The CMOS began to
get hot, as did the motor ("hmmm ... maybe I should unplug this, it's getting
hot ... naw, it's rated for a hundred degrees above ambient"). Then there
was a *crack* fizzle and a cloud of smoke.
   The CMOS was fried without exception, but the drivers and the motor were
OK. So, I (fool that I am) replaced the dead login with slightly more complex
software and tried again -- with a good limiting resistor this time. It worked,
and I went on with the project.
   A while later, I had just turned on the Timex, and was having trouble
getting it to respond to its keyboard. (I had long since replaced the
membrane keyboard with a "real" keyboard that happened to have a similar
matrix layout. The computer was unrecognizable as a ZX81 to anyone who
wasn't *used* to seeing them with their cases off...) And all of a sudden,
another flash of light, a sharp *CRACK*, and a neat conical piece flew out
of the top of the thing's custom glue chip. Apparently the power supply,
abused by the lack of a current limiting resistor, had chosen that moment
to get back at me by quintupling the supply voltage to 25 volts. 
   Fortunately, with a ZX81, I could just go down the street and buy a few 
spare machines for $5 from people who had some in their closets =8)
I still have that cratered chip ...


-- 
wi...@blake.acs.washington.edu        (206)526-5885      Seattle, Washington