TM11-6125-256-34
Troubleshooting
Voltage
Measurements
(1) Measure the voltage across terminals T1-3 and
T1-4 (28 volts ac), and across terminals T1-5 and T1-6
A pointed probe will be required to puncture the
(65 8 volts ac) If either voltage is too low, check for
protective coating when making voltage, continuity, and
shorted associated diodes CR8 through CR15 If diodes
resistance checks. After repairs are completed, this
are not shorted, check for shorted transformer T1
coating must be restored in accordance with paragraph
Resistance from T1-3 to T1-4 and from T1-5 to T1-6
4-10 step f
should be 1489 2 to 2014 8 ohms
(2) If the voltage in step (1) is correct, measure the
voltage across resistor R6 The voltage should be
approximately 12 5 volts dc If the voltage is incorrect,
check diodes CR8 through CR11, resistors R4, R6, and
R15, and capacitor C4
(1) Measure the voltage across terminals T1-7 and
T1-8 The voltage should be approximately 0 042 volt ac
If the voltage is too low, but the input to transformer
(3) If the voltage in step (2) is correct, measure the
(terminal 1 to ground) is as specified in paragraph 4-7,
emitter-to-base voltage across transistor Q2 This is the
step c(3) check for shorted rectifier CR1 or CR2 or
frequency regulator control voltage and should be
shorted capacitor C1 If these components are
approximately 0 65 volt dc with the transistor cut off
functioning properly check transformer T1 for shorts
(emitter negative with respect to base) If the voltage is
Resistance from T1-1 to T1-2 should be between 3917
incorrect, check capacitor C3 C4, C6, inductors L1 and
and 4887 ohms Resistance from T1-7 to T1-9 should be
L2 resistor R6, and diodes CR7, CR12 through CR15
between 1149 2 and 1554 8 ohms
and CR26 and transistor Q2
(2) Measure the voltage across capacitor C1 The
voltage should be approximately 0 37 volt dc If the
(4) If the voltage in step (3) is correct check
voltage is too low, check for open rectifier CR1 or CR2 or
transistors Q4 and Q6 resistors R11 and R13 and diode
open capacitor C1
CR20
4-9. Removal and Repair
(3) If the voltage measured in step (2) is as specified
a Shut off dc input power
measure the base-to-collector voltage for transistor Q1
This is the voltage regulation control voltage and should
be approximately 0 38 volt dc with the emitter positive
with respect to the base In addition measure the emitter-
assembly from the motor-generator as described in
to-ground voltage The voltage should be approximately
paragraph 3-11a
0 76 volts dc If either voltage is incorrect check resistors
R1 R2, R3, and R14 Check resistance of diodes CR3
and CR4 in both directions to ensure that they are not
c Remove self-locking nuts (21 fig 4-5) screws (19,
open or shorted Check that breakdown voltage of Zener
25 and 26), lock washers (22), washers (23) loop clamp
diode CR5 is 8 55 to 9 55 volts dc at 7 5 milliaperes and
(28) electrical lead (27), and sleeve spacers (24)
that transistor Q1 is not shorted
d Without stressing wiring harness (61) leads,
(4) If the base-to-collector voltage for transistor Q1
position printed circuit board subassembly (29) so that
measured in step (3) is as specified check transistors Q1
components can be unsoldered
Q3, and Q5 and resistors R9, R10, R12 Check resistance
of diodes CR16 through CR19 and CR21 in both
e Check the suspected component(s) Section VI gives
directions to ensure that they are not open or shorted
the electrical component test values for the voltage and
frequency regulator assembly components
b Frequency Regulation Circuit If the voltage
f Check to see that replacement parts are available
regulation circuits are functioning properly, check
frequency regulation circuits as follows
To replace the faulty parts proceed as follows
