Play Meter

By Doug McCallum
How to find those pesky shorts
Editor's Note: Operators still in
possession of some of the electro-
mechanical games may find this
article on shorts helpful. However ,
the information does not apply to
solid state games .
Shorts and their symptoms (circuit
path interruptions due to faults in the
current limiting circuitry - also known
as blown fuses) can be exasperating
little devils to figure out, and I regret
to announce there are no simple
ways to find them.
However , I herein offer some tips
and techniques that should help . I
will limit this essay to 24 volt shorts,
but light shorts (six volt) can be dealt
with similarly .
First , shorts come in different
types : the dead short , the "slow"
short (blows the fuse after a couple of
seconds rather than immediately) ,
and the occasional short (blows fuse
only when the shorted path is turned
on).
Dead shorts can be tough - often
they can't be helped by the schema-
tic . As with any short we use a
breaker .
First look for loose quarters or
hardware lying about , nuts and bolts
seem to fall across relay blades while
quarters usually find their way under
jones connectors and other goodies
near the front , but you never know .
If nothing obvious shows up and you
dori't see any burnt up coils, it
becomes time to isolate the prob-
lem - unplug the playfield .
Short still there? Unplug the
head ... short still there? Time to
check out the mechanical board .
Once you've found where the
short is (say , the playfield) you can
further narrow it down by figuring out
which jones plug carries the shorted
line .
Many machines, especially Bally
and Williams, list jones plug connec-
tions either on the schematic or in the
instruction manual. Once you nar-
row it down to a few wires , you
should have no trouble finding which
one is shorted and where . Just
think - you're done before lunch .
Slow shorts are found similarly but
an ammeter is a better tool than a
circuit breaker because you don 't
have to wait for the breaker to blow .
Occasional shorts are the best.
Generally, you can associate them
with some activity (pop bumpers,
advance bonus, whatever) , which
are simple enough. Sometimes it
involves the scoremotor (reset se-
quence , etc .) No problem : pull out
the scoremeter service jack and step
the scoremotor around slowly by
hand . When you find which stack
controls the short , look it up . Most
games have scoremotor contact
listings either in the schematic or the
instruction book .
If these basic maneuvers fail , well ,
take your lunch break and stick with
it - it's time to start unhooking wires .
When you have something like a ten
point line shorted you have no
course but to disconnect and thus
isolate areas of the machine and , ta
da , if you keep narrowing it down ,
you 'll find it , by golly .
Technical tip on Atari's LUNAR LANDER
There is a letter in a square on the bottom of the main PCB near the
edge connector : A , B , or C . If your board is A or B , perform the
following modification to protect the 4016B in location A 12 from excessive
input voltage .
Install (2) ln914 diodes next to the device in location B-11 as shown .
B- 11
- -•Ill Ed ge connecto r
AD561JD
-1
.1 uf
Add { 2 ) 1N914's
r
'It Band same end .
.;j
-c=o-)
---1)1-
Note : DO NOT replace the 4016B's with 4066's . Switching characteristics
of the 4066 make it unacceptable for use in sample and hold circuit
applications .