Star Tech Journal

I did run across one interesting thing: the
coin door lamps use the 6.3 VAC to light up,
and their sockets appeared a bit faulty so I
cut their wires and took them out of the
circuit. But that did not help light up the
picture tube's heater.
I finally got a break a few days later when the
heater fuse blew. When I replaced it, the
heater came on! What happened? I con-
cluded that the fuse's internal resistance
had slowly increased, thereby dropping the
voltage across it. Instead of blowing the way
it should have, this one just slowly weak-
ened. I didn't notice this before because the
beeper-continuity function on my DVM
turns on the beeper when it finds anything
under 30 ohms across the meter leads.
Ideally, a fuse should be very close to zero
ohms (although some fuses with very small
current ratings are about 10 ohms), but this
one had apparently slowly increased to sev-
eral times what it should have been. Since its
overall resistance had not yet gone over 30
ohms, however, the beeper on my meter
turned on and I assumed the fuse was good.
So now, when I check a fuse, I don't use the
continuity test and instead get a direct resis-
tance measurement.
My dad is a retired engineer from a Texas
electric power company and I asked him ifhe
ever ran across a fuse doing this. he said an
electrical substation in west Texas got
knocked out for a while because a fuse
developed a cold solder joint inside one of the
endcaps and increased its resistance. But
since it wasn't visible, no one caught it by
just looking at it. He also says that the same
thing can happen in circuit breakers.
Steering Wheel
"Shifter"
HAPP CONTROLS Manufacturer and Distributor of Game Controls
106 Garlisch Avenue• Elk Grove Village, IL 60007
Phone: 312/593-6130 • Telex: 297-249Ur • Fax: 312/593-6137