Star Tech Journal

May 1997
STAR* TECH JOURNAL
Enzo.,s
Tech
Tips
"Hey Enzo, I can't find the self-test button on this Captain Fantastic!,,
Douglas 'Enzo' Mccallum • Shiawassee Technical Services • Lansing, Ml
SEt IING UP A COIN-OP SERVICE BENCH (PART
6)
EQUIPPING THE BENCH - POWER SUPPLIES
Ours is an electronics bench, so
everything on it needs power to
function. Some units we service
are self contained, so all we need
is a wall outlet to power them up.
Everything else will need a
power supply.
• Monitors just require an
isolated AC source.
• Switchers can run right off
the AC line, but you should
use an isolated supply to al-
low your 'scope access.
As I have written before, servic-
ing both those items is made
easier with the addition of a
Variac to the isolation setup. A
Variac offers no isolation by it-
self. Proper practice is to plug
the Variac into the isolation trans-
former, NOT putting the iso af-
ter the Variac.
For logic boards, you need what
the game has: a sturdy SV sup-
ply along with 12V and maybe
others. Easiest thing to do there
is just bench mount a switching
supply of suitable rating. I keep
several handy.
One is for general use. It has a
set of clip leads permanently at-
tached to the outputs. I use it for
video game logic, pinball logic,
all kinds of things.
Volts is volts and amps is amps.
Ripple and regulation percentage
is not the issue, they really aren't
much of a factor. Our stuff is
pretty tolerant in those areas.
The manufacturers put switchers
in the games because they are a
lot cheaper. A whole switching
supply costs less than just the big
transformer of a linear. Many lin-
ear supplies are more tolerant of
shorts across their outputs than
your typical switcher.
I have a couple dedicated
switcher supplies, which is to say
they are wired up for a specific
application, such as my Merit Pit
Boss/Trivia rig. If you have a com-
mon logic repair setup, such as a
JAMMA rig, you might dedicate
a switcher to that. By the way,
there is absolutely nothing wrong
with an old linear supply, either
on your bench or in a game.
Some years back I needed a 12
volt supply for something with no
time to build one. I bought a
small regulated supply from Ra-
dio Shack. I added a pair of bind-
ing posts on the front panel for
convenience. I use the little
sucker all the time. As power for
Deltronics ticket dispensers for
example. It sits on top of my
bench meter.