STAR•TECH JOURNAL/MAY 1982
7
MIDWAY'S
"X-Y" MONITOR TROUBLESHOOTING TIPS (CONTINUED)
Solving Very Difficult Monitor Problems
Based on practical experience and a loud response
from the field, it would seem that the " X -Y"
monitor may be easy to understand but difficult
to fix. And it is! While in service it may develop
the usual easy-to-fix problems, most of which
have already been covered in previous parts of
this series in Star*Tech Journal (Feb., Mar.,
Apr. ' 82). BUT-sometimes it develops almost
impossible-to-fix catastrophes . On one day they
may be found fairly easily; the next, you may not
be so lucky.
To try to give you some insight into some of
these " catastrophes" and their cures, let's peruse
the monitor circuit by circuit.
THE SPOT KILLER doesn't seem to cause
much trouble with the exception of the LED,
D 504. It can't be checked by the usual ohmmeter
method because it reads infinite resistance both
ways.
If your dipswitch test pattern does not want
to come in, or your brightness just doesn't seem
bright enough, and EVERYTHING EVERY-
WHERE ELSE checks good, pull out D 504.
Chances are you'll have plenty· of brightness.
Poor brightness with retrace lines could mean
a defective D 504, or perhaps the " Z" signal
wire isn't connected properly to the base of
Q504.
EHTorHIGHVOLTAGE UNIT. It is reported
that the weakest part of these monitors is the
EHT or High Voltage Unit. This may be because
the secondary windings tend to open up or arc
due to poor mechanical connections.
The first condition will cause no picture
WITH high voltage depending on which secondary
opens. The second condition will cause " bloom-
ing" , a faded enlarged picture.
POWER SUPPLY. If your picture appears as if
the "Omegans" are having a 4th of July fireworks
display, it is probably a bad Power Supply.
Trouble with C 100 or C IOI will cause the
lines to brightly streak around, possibly coming
from a spot in the center. If a proper picture is
present on the monitor but moves around and
blooms, it could be a partially open C 100 or
C 101 . The other circuits are starving for voltage
and not totally doing their jobs.
"X" and "Y" AMPLIFIERS. If the top,
bottom, or sides of the display flutter and try to
move toward the center, again, check the Power
Supply. More often, though, this situation is due
to a bad transistor in the "X" Amplifier (sides)
or the "Y" Amplifier (top and bottom). Some-
times these circuits will check good with an
ohmmeter.
So, if a team of engineers with sophisticated
test equipment are not available, this is our
suggestion: change Q 707 and Q 706 for the
" X" Amplifier - or - Q 607 and Q 606 for the
"Y" Amplifier. Q 605 and Q 705 are also sus-
picious characters . If the above doesn't work, try
them next.
When changing Q 706, Q 707, Q 606, and
Q 607, ALWAYS make sure you have each one
in its proper place with the correct lead placement.
If you do not, you may as well break out the hot
dogs because you WILL have a barbequed
Deflection P.C. Board!
If you should happen to barbecue a Deflection
Board, CHECK ALL SEMICONDUCTORS
in that particular amplifier. Also check all res'is-
" X " or " Y" amplifiers can cause R 10 I to bum
up. Depending on the problem, it may bum fast
or it may bum slow. Jumping these resistors may
may live to regret not having done it.
stop them from burning up but it WlLL NOT
Remember this. If at first you do not get a solve the problem.
picture and the LED on the monitor (D 504) TRANSISTORS that CHECK GOOD with a
stays lit, every time you go back to determine meter but are NOT GOOD in the circuit is a
what else has failed in this amplifier circuit, condition that is generally rare elsewhere. But
ALWAYS check the output transistors Q 608, maybe not so rare in the "X-Y" monitor. This is
Q 609, Q 708, and Q 709 because you can mentioned because we know it is a problem
destroy them as fast as you replace them.
encountered frequently with the "X-Y" monitor
SEMICONDUCTORS. A defective semicon- and we want to bring it to your attention.
ductor that checks good on the ohmmeter may VOLTAGES. For any of you who would like to
also drag down the Power Supply voltage. Check try a little voltage measuring to analyze the
the collectors of the output transistors. If two problem, the following list contains EVERY
voltages are high and the other two are low, it Electrohome and Wells-Gardner " X-Y" monitor
could be a defective transistor at Q 602, Q 603 , transistor voltage. These voltages were measured
Q 702, or Q 703 .
on correctly functioning monitors with a hand-
WELLS-GARDNER MONITOR. The Wells- held portable digital multimeter. So, these readings
Gardner Monitor has two large resistors in the are accurate (but not laboratory accurate) and
Power Supply, R 100 and R 101. R IOI just will be closer to your actual expected voltage
loves to smoke and bum up. WHY? Check the measurement results.
30-volt lines from the game. If one is open, there
For a test display, the diamond shaped test
will be a NORMAL picture and ONE VERY pattern is used so that the voltage readings will
HOT resistor.
stay stable and not jump around as they would
Another symptom that can cause R IO 1 to with a moving game picture. Of course, you
start smoking is when the Daughter Board of the cannot see a picture with a defective monitor, so
game has an "X" or "Y" signal riding on an connect a D.C. voltmeter to the "X" channel on
excessively high D.C. level.
the Daughter Board output. When you have the
Then again, any one of the conditions men- correct diamond shaped test pattern, you should
tioned previously pertaining to problems in the be reading a steady -2.23 volts on your meter.
tors from R 721 at least as far back as R 705
("X" amplifier circuit) or R 621 back as far as
R 605 (" Y" amplifier circuit). Otherwise, you
Electrohome "X-Y" Monitor
Wells-Gardner "X-Y" Monitor
All Readings Are D .C. Level Voltages
All Readings Are D .C. Level Voltages
" X" INPUT D .C . LEVEL FOR DIAMOND
TEST PATTERN= -2.32 VOLTS D .C .
"Y" INPUT D.C. LEVEL FOR DIAMOND
TEST PATTERN= -0.08 VOLTS D .C .
"X" INPUT D .C . LEVEL FOR DIAMOND
TEST PATTERN= -2.32 VOLTS D .C .
" Y" INPUT D .C. LEVEL FOR DIAMOND
TEST PATTERN= -0.08 VOLTS D .C.
B = BASE
E = EMITTER
C = COLLECTOR
B = BASE
E = EMITTER
C = COLLECTOR
0 601 B - 0.3
E - 0.6
C + 0.5
0 701 B - 1.40
E - 1.88
C + 0.528
0500B - 1.3
E 0.0
C +38.7
0 602 B - 0.105
E + 0.72
C +32.2
Q 702
B - 0.772
E - 1.39
C -28.9
Q 500
Q 602 B - 0.034
Q 702
B - 0.6
E - 1.2
C +39.0
Q 501
B - 0.655
E 0.0
C +38.7
0 603 B - 0.096
E - 0.710
C + 32.4
Q 703
B - 0.783
E - 1.37
C +32.4
0 501 B - 2.6
E 0.0
C +34.6
Q 703
B - 0.6
E - 1.2
C +38.8
Q 502
B + 38.8
E +39.8
C + 1.4
0 604 B - 29.5
E - 30.2
C - 29.6
0 704 B - 29.7
E -30.4
C - 28.9
0 502 B + 34.5
E + 1.6
C +33.2
0 704 B - 39.3
E -39.9
C -27.1
Q 503
B + 2.1
E + 1.4
C + 1.4
0 605 B +32.3
E +32.9
C +30.5
0 705 B +32.5
E +33.2
C +30.5
0 503 B + 0.733
E - 0.16
C + 0.16
0 605 B +38.8
E + 39.5
C +36.0
Q 705
0504 B + 2.3
E + 1.8
C +75.3
0 606 B +30.0
E +30.6
C + 0.222
Q 706
B +30.0
E -30.4
C - 1.34
0 504 B + 2.3
E + 1.74
C +77.0
0 606 B +35.4
E +36.0
C + 0.22
Q
Q 900
B +23.0
E +22.1
C +32.1
0 607 B - 0.54
E - 30.4
C -29.7
Q 707
B - 30.4
E -29.7
C - 2.09
Q 900
0 607 B - 39.4
E -40.0
C - 0.4
Q 707
B - 39.4
E - 40.0
C - 1.72
Q 901
B +23.6
E +22.9
C +31 .8
0 608 B + 0.20
E - 0.13
C + 34.6
0 708 B - 1.34
E - 1.67
C +34.7
0 901 B +16.6
E +16.0
C +24.0
Q 608
0 708 B - 1.0
E - 1.34
C +41 .0
Q 902
B + 9.2
E + 8.7
C +24.1
0 609 B - 0.54
E - 0.14
C -31.5
Q 709
0 902 B + 9.7
E + 9.2
C +16.6
Q 709
0 903 B - 3.4
E 0.0
C +22.4
E - 0.629
C + 38.8
Q 603 B - 0.627
E - 0.034
C +38.6
Q 604 B - 39.3
E - 39.9
C -27.4
B + 0.246
E - 0.075
C +41 .1
Q 609 B - 0.464
E - 0.069
C -41.2
B +39.0
E +39.7
C +36.2
706 B +34.1
E +36.2
C - 1.0
B - 1.7
E - 1.3
C - 41 .1
B - 2.08
E - 1.68
C - 31.7
B - 3.5
E 0.0
C +34.6
B +16.0
E +15.3
C +24.2
0 903 B - 3.8
E 0.0
C +15.0