Star Tech Journal

17
STAR*TECH Journal APRIL 1982
PARTS INTERCHANGEABILITY
to jump around like crazy when the game is being NOT check the anode voltage unless you have a
played or is running through its ATTRACT special high voltage probe or you may wind up
mode, so using the test pattern tends to keep them repairing X-Y monitors in heaven.
still.
DO NOT BE FOOLED by the silent operation
Next, use the volt meter to make sure the other of the monitor. Regular T.V. sets and monitors
voltages are present at each pin. Similarly, you buzz and crackle a lot when they're operating -
proceed to P500 on the deflection board, and this is normal for them. BUT, vectorbeam monitors
P900 on the EHT unit to make sure all the are noiseless unless something is wrong.
correct voltages are present. Use the schematic
to determine what the correct voltages should be.
Whatever you do, ALWAYS read the literature
Check the pins on the CRT to be sure the that comes with any test equipment you use so
voltages are getting this far. If everything looks that you will not damage the equipment, the
good to this point, perhaps the CRT is bad. DO monitor, and most of all, YOURSELF.
Quite a few of the parts between the Electrohome
and the Wells-Gardner monitors may be swapped.
The CRTs, for example, are completely inter-
changeable. Also, many of the transistors used in
each monitor are the same. Certain critical
components in the power supply and the EHT
unit are dangerous to interchange. The best thing
to do is to compare both monitors' parts lists to
see if the descriptions of any two particular parts
you want to swap match exactly. Substitution
manuals are available for transistors and semi-
conductors, but you never know about them.
Sometimes they work and sometimes they don't,
depending on the critical circuit parameters. If in
doubt, order exact replacement parts.
MIDWAY
"MS. PAC-MAN": PCB LAYOUT, DIFFICULTY MOD
"Ms. Pac-Man" PCB Layout
"Ms. Pac-Man" Difficulty Level Mod
Subject "Ms. Pac-Man" Main Logic Board
(PC A082-91375-BOOO)
In order to increase the level of difficulty with
which your "Ms. Pac-Man" game plays, a
jumper wire must be installed as described
below.
I. The main "Ms. Pac-Man" logic board is
the same logic board as in "Pac-Man".
• 2. There are two minor changes:
A. Character Proms at 5E and 5F are
"Ms. Pac-Man" type.
B. The 280 is removed and inserted into
"Ms. Pac-Man" auxiliary board (PC
A084-91415-B617).
NOTE - All "Ms. Pac-Man" will be shipped
with static filter boards.
3. Solder in a jumper wire connecting the two
halves of the pad.
NOTE: If you are not sure if you'll want to
leave the jumper wire connected or not, you
may wish to install a small toggle or slide
switch in your jumper wire and secure it to the
cable harness to keep it from shorting out any
components on the Main Game Logic Board.
NOTE: Installing this jumper wire will
definitely make your "Ms. Pac-Man" game
CONSIDERABLY more difficult to play.
However, if you desire a more difficult game
(say, one for ADVANCED players), the
jumper wire may be installed as follows:
4. When finished, reinstall the Main Game
Logic Board.
1. Remove the Main Game Logic Board.
2. Remove the coating of green insulatory
material over the two halves of the jumper
pad shown in Figure I. BE CAREFUL
NOT TO DAMAGE THE FOIL OF
THE JUMPER PAD IN ANY WAY.
0
FIGURE 1
,...a...,
:____J
i
~
~-
·-=·
:
:
I
ij
0
i:=:
:-==-..:
~ ~:
(..10
~
+
: =::-:
·11·
DIP-SWITCH
Rl-16
'/C
t
74LS/6I
INSTALL JUMPER WIRE TO
CONNECT BOTH HALVES
OF INDICATED JUMPER PAD.