Precision Trading 60 R3.0 - Manual (Page 55)

Operator Manual, Supercharger 60 R3.0
Page 55 of 62
10.2 FINDING A SHORTED DISCHARGE TRANSISTOR
Since all discharge transistors are wired in parallel, a single shorted transistor will short
the entire bank.
The procedure that follows will allow the finding of the shorted transistor without
requiring removal and testing of each device individually.
10.2.1. EQUIPMENT REQUIRED
• Digital Voltmeter.
• Battery, 24V.
• Lamp, 24V (lamp must draw at least 0.5 A).
10.2.2. PROCEDURE
10.2.2.1. TURN UNIT OFF, DISCONNECT IT FROM THE WALL OUTLET.
10.2.2.2. Connect the lamp in place of the discharge current limiter (see fig 8).
10.2.2.3. Connect the charger to the battery.
10.2.2.4. If the lamp illuminates, it indicates that there is a short in the discharge
circuit, generated by one or more shorted transistors.
10.2.2.5. Measure the voltage across the individual .22 OHM emitter resistors
(RED-RED-GOLD-GOLD) (see fig 8).
• A non zero reading, approximately 0.1V for a lamp drawing .5A,
indicates current flow due to a transistor with a collector to emitter
short.
• NOTE: A non zero reading on all emitter resistors (0.02V approx
for a lamp drawing 0.5A) indicates a different failure mode
(collector to base short; refer to step 7).
10.2.2.6. Remove any shorted transistors and repeat steps 4 and 5 until a no
short reading is obtained. Replace defective devices only with
transistor type MJ15023.
10.2.2.7. If all transistors appear to be shorted (ALL emitter resistors reading a
voltage), then, one or more have failed with a collector to base short,
causing the remainder of the transistors to turn on. It will then be
necessary to check each transistor individually.
• This can be greatly facilitated by searching for a zero reading. This
will indicate the shorted device.
10.2.2.8. When replacing transistors, make sure that the base and emitter pins
engage properly in the socket contacts. Add heat sink compound and
torque the screws properly to insure a good thermal transfer.
• NOTE: If replacing any of the control transistors (Q1 and Q2),
note that they are mounted with a mica insulator.