Star Tech Journal

SlJiR.TECH _ _ _ _ _ _ _ _ _ _ 5
Burned 47ohm Resistors in Current Amplifiers
A common failure of the current amplifier, especially on older
monitors, is blowing of circuit breakers CB1 and CB2
accompanied by burning of 47ohm resistors around the power
transistor molex.
The power drivers should not be unplugged during game
operation, or the same resistors will be overdriven and
eventually burn. Check for cracked solder around the molex
pins. With an ohmeter or transistor tester, verify that the power
transistors are operational; this is best accomplished by
disconnecting the molex plug and checking right at the pins. The
row of pins with the lone male pin always indicates the 2N5878
driver. The row of all female pins indicates the 2N5876 power
drive.
Check on board drivers 0108, 0109, 0208 and 0209 with
ohmeter or in-circuit transistor tester. Upgrade 47ohm resistors
from¼ watt to½ watt if not so equipped.
High Voltage Section - Regulators
On older Cinematronics monitors incorporating a high voltage
cage and associated components, a substitution may be made
for the +18 (7818) and -18 (7918)) volt regulators if unavailable.
IC3, the +18 volt regulator, may be replaced by a +15 volt
regulator, 7815. IC 5, the -18 volt regulator, may be replaced by
a -15 volt regulator, 7915.
There will be a 20% decrease in overall output levels that does
not degrade game performance. Potentiometers R102 and R209
may be adjusted to compensate for increased screen size. Verify
that resistors R12 and R13 are rated at 4 watts as there will be a
20% increase in power dissipation.
Low and Lost Voltages
"477-478" Rock-Ola
by Chuck Maier
Dim display lights and slow D.C. motors are problems that can
be caused by the regulator board.
0203 is a PNP darlington transistor that is used in the -21
VDC circuit that powers the displays. 0201 is an NPN darlington
transistor that is used in the +32 VDC circuit that powers the
motors.
Both of these transistors are mounted horizontally on the
power supply's regulator board. They also have a "U" shaped
heat sink installed. Poor solder and/or the weight of the heat
sink and its lack of support has caused the leads of these
transistors to break loose from the board. A new "Z" shaped heat
sink is used on later models to prevent this.
Resolder the board and if you care to change the old heat
sinks to the new number (Rock-Ola #51631-2) do so. At the
same time check the leads of the transistors for sharp bends as
they may cause the leads to break and open the circuit.