14
same indications apply to refrigerators, oil burners, washing machines, ventilat-
ing fans, air conditioning systems, air compressors, water pumps, vacuum clean-
ers, heaters, irons, toasters, waffle irons, food mixers, lighting circuits, heat lamps,
radios, televisions and all devices which use a motor or transistorized circuitry.
The wattmeter section may also be used as an indicator for problems with solid-
state radios, stereo sets or television receivers. A high wattage drain would
indicate a shorted transistor or improper bias, while a low wattage drain would
indicate an open transistor or circuit. Many manufacturers include possible clues
pointing to faulty circuits with certain wattage readings.
5.
THEORY OF OPERATION
5.1
AC And DC Voltmeter Circuit
Figure 5-1 shows the circuit used when making voltage tests. The multiplier resis-
tors for the 150V and 300V ranges are wound to match each meter. The WATTS
and AMPS pushbuttons are in the normal (out) position and the contacts of these
switches complete the circuit.
Figure 5-1. Simplified Voltmeter Circuit
5.2
AC Ammeter Circuit
Figure 5-2 shows the ammeter circuit used when the AMPS pushbutton is de-
pressed. This connects the meter to transformer T1. When all turns of the primary
winding are connected, the 3 ampere range is provided. The center tap provides
the 15 ampere range. Resistor R6 is used for calibration.
Figure 5-2. Simplified AC Ammeter Circuit
300V
R1
R2
R3
R4
R5
150V
S1
S2
+V
FIELDS
ARMATURE
–
–
S1 DEPRESSED
ARMATURE
FIELDS
R6
3A
15A
+A
T1