a. Inspection. Inspect the synchroscope (114, figure
5-1) for loose electrical connections and damaged or
Connect the synchroscope as shown in figure
5-17 test setup. Frequency generators used
should be capable of providing minimum 50
volts, maximum 240 volts. Frequency 0 to 60
Hz. For testing the pull-in frequency is 48 Hz,
the drop-out frequency is 47 Hz.
The synchroscope axial polarizing coils are
energized from the 'incoming' frequency,
while the radial field coils are connected to the
'running' circuit. If there is no difference
between the two circuits either in phase angle
motionless at the 12 o'clock position on the
dial. With no frequency difference, any phase
angle difference will cause the pointer to take
up a position away from this point. If,
however, there is a difference in frequency,
this phase relationship will be constantly
changing and the pointer will consequently
rotate continuously in one direction or the
other at a speed corresponding to the
difference in frequency. If incoming' is at a
higher speed than the 'running', the pointer
rotates clockwise, and counterclockwise if its
speed is lower.
When the lamps turn off together, the two
'incoming' frequency has been adjusted to
equal that of the 'running' frequency, the
pointer will come to rest at a point on the
scale depending on the phase displacement of
the two voltages. The speed of the 'incoming'
must then be inched up or down until the
pointer takes a steady position at 12 o'clock.
Replacement. To remove the synchroscope from
the generator panel, tag and disconnect wires, and
remove attaching hardware. Replace in generator
panel with attaching hardware and reconnect
wires. Remove tags from wires.
5-9. RESISTOR AND DIODES. Resistor (26, figure 5-
1, sheet 1) and diodes (25) are all mounted on terminal
boards (24) on the rear wall of the enclosure. They are
removed by unscrewing them from their terminals on
Test resistor (26) by measuring with an
ohmmeter. It should be 39,000 ohms ±5
Test diodes as follows:
Disconnect one end of the diode.
Connect an ohmmeter (scale. set Rx100)
across the diode, note the reading. Now
reverse ohmmeter leads to the diode, and
again note reading. A good diode will read
high resistance one way and low resistance
the other way. A shorted diode will read full
scale both ways. An open diode will read
infinity (no reading) in either direction. Check
all diodes and replace disconnected leads.
5-10. DIGITAL CLOCK.
Connect clock in test setup shown in figure
Close switch S1 to test 60