SYMPTOM
FAULTS
TREATMENT
No Reading
(contd.)
Resistor R9
Capacitor C3
Diode Dz
R5 and R8
C1
C2
R2
R7
R6
Component defective M,
Th1, R3, TR1, TR2
Meter M
With the supply OFF check resistance
value -6v and -12v terminals. This
should be 82 ohms.
Disconnect one side of C3 and switch
the supply ON. If the voltage across
Dz is between 4.7V and 5.1V, C3 is
faulty. If the voltage is still less
than 4.7V, reconnect and test Dz.
Disconnect one side of Dz and switch
the supply ON. Measure the voltage
across C3. If it is more than 4.7V
change Dz, if not proceed to test
R5, R8, C1, R2, R7 and R6.
With the supply OFF check the
resistance between A & G. On
adjusting R8 the resistance should
vary between 6K and 22K. The value
of R5 should read 5K.
With the supply ON check the voltage
across C1. This should be at zener
potential approximately.
Check for short circuit. Replace if
necessary.
With the supply OFF check the
resistance between A and the left
hand of C1. This should be 1320 ohms
– 1080 ohms.
With the supply OFF check R7 between
H & G. Resistance should be 3.3
ohms.
With the supply OFF check R6 between
G & 6v terminal. The resistance
should
be 18 ohms.
With the supply ON and D shorted to
earth. The Tachometer should read
8000 r.p.m. If it does the
components are satisfactory, if not
proceed as follows:
With the supply ON, short point C to
earth. If the meter reads, it is
satisfactory and the fault lies in
R3 and it should be replaced.
S.13
