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and the lamp. When the lamp lights, you've identified a
break in the lamp wiring. The break is in the section of
game wiring paralleled by the jumper wire.
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• CHECK THE SCR.
If you suspect a bad SCR, jump
from CPU Test Point 7 to the SCR gate.
Lamp doesn't
light:
Replace the SCA.
Lamp lights:
The 2K gate
resistor or 4514 decoder may be faulty. Suspect the
resistor first. Check its resistance. If the resistor reads
more than 3K, replace it. If a group of lamps is out,
then suspect a bad decoder.
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..
•
•
.CHECK THE
B
+
CONNECTION.
Still no light? Find
a known-good lamp with the same phase (A or 8) as
the inoperative one. Connect a jumper to the anode of
that lamp's diode. Touch the free end of the jumper to
the diode anode in the malfunctioning circuit.
Lamp
lights now:
If the malfunctioning circuit now produces
light, 20VAC wiring to the circuit is open.
In each case, if your hunch is correct, the jumper causes
the lamp to light.
To restore normal operation, replace the
faulty part.
•
SYMPTOM: ONE LAMP ALWAYS ON
Connector numbers are displayed during the Single Lamp
Test. Watch for the connector that corresponds to the mal-
functioning lamp circuit. It will be one of four connectors.
Disconnect this connector at the SCA. Don't be surprised if
both A and
8
lamps associated with this connector remain
on. If so, there's a short between either diode and its lamp
socket. The brighter lamp is connected to the short.
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However both lamps may light with equal brilliance. If so,
you have a short from the cold side of the lamps to ground.
Sometimes you'll find the short between the lamps and con-
nector CJ. Otherwise the short occurs between the connec-
tor and ground. Unplug the connector .
• If the lamps remain on, the short occurs on the lamp
side of the connector.
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