Star Tech Journal

October 1995
CID
STAR*TECH
Journal
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TROUBLESHOOTING WMS
T2 PINBALL
Tech Library
SWITCH MATRIX VIA THE INTERNET
STAR* TECH Journal's
Tech Library comes
complete with every
service manual
published.
Jonathan Deitch, a frequent contributor to STAR*TECH]ournal and an
Atlanta, Georgia games technician, troubleshoots a problem for Andrew
Davis of England via the Internet. Noteworthy because this point-to-point
method works not only on Terminator 2 but other pinball games as well.
SAVE OVER
SYMPTOMS
ANDREW J DAVIS WRITES:
One column on the switch ma-
trix (i.e. all 9 rows) says there is
an earth short in the test mode.
This includes all the pop
bumpers and the sling shots.
Game play is affected just a tiny
bit...
Just before the problem surfaced
I stupidly changed a few bulbs
with the power on. I managed to
give myself an electric shock
(from an under cabinet lead)
against the metal strips the glass
seats in.
Could this have caused a melt-
down on a board? (All the fuses/
boards seem to look OK) Or is it
more likely I've shifted the return
feed for the 9 rows against an
earth?
SOUITION
JONATHAN DEITCH REPLIES:
Well ... first of all, if an *entire*
column is shorted, that's a sure
sign of a bad output on the ULN-
2803 chip used as the switch col-
umn driver.
What most likely happened is
that you accidentally shorted that
switch column to one of the coil
outputs. This is real easy as a
bunch of switchesare *right* next
to flashlamps, in particular.
25%
For more information
see page 23.
PROCEDURE
First thing you want to do is to
unplug the switch column and
switch row plugs from the bottom
of the CPU board.
Theses are the plugs across the
very bottom and they're labeled.
Leave "cabinet" plugged in as
that's the direct switches on the
coin door. Now check in switch
edges, where the switch chart is
on the DMD. This'll tell you if
any switches are on.
STAR* TECH Journal
neither operates, dis-
tributes nor manufac-
tures coin-operated
equipment. It's sole pur-
pose for being is to com-
pile technical and infor-
mational data consid-
ered valuable for dis-
semination to its paid
subscribers. Comments
or suggestions pertain-
ing to this service are
always welcome.
~
~
There shouldn't be.
Now plug in everything BUT the
switch column drive. See if any-
thing shows up as on. Again, it
should not. IF so, then start look-
ing for a ground short. Lastly plug
the column drives in and see if
your bad column immediately
goes all on. This means the col-
umn drive has gone bad.
To fix, if it's the column drive,
remove U20, a ULN-2803, re-
place with a socket, & insert new
chip. It should be as good as new.
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