Connect a multimeter (set to read 050
VDC) across points "A" and "B" as
indicated on wiring schematic. Connect
red lead to point "A" and black lead to
(I) A DC voltage of 28-32 volts should be indicated. If
voltage is not within this range, check the
voltage across voltage regulating (zener)
diode VR1 and VR2 on circuit board.
ner diode VR1 or VR2 is removed, do not apply the 115 VAC source
to the regulator until a replacement is connected
into the circuit. Failure of the voltage regulator will
occur if this caution is not observed.
The voltage across VR1 and VR2 should
be approximately 14 VDC. Replace zener
diodes that do not have a voltage drop of
approximately 14 VDC.
After replacing zener diodes VRI and/or
VR2 and no voltage is indicated across
either or both zener diodes VR 1 and
VR2, check the voltage across terminal
lugs #7 and #8 of the T 1 power
tting on multimeter to 0-50 VAC range.
A voltage of 25-35 VAC should be present.
If voltage is not present, check that 1 15
VAC power source is connected properly
and all wiring connections to T1 (6) are
tight. If power is properly connected and
T1 (6) connections are tight, transformer T
1 (6) should be replaced.
After verifying that 25-35 VAC is present
across T1 (6) terminals #7 and #8, locate
diodes CR8 and CR9 on circuit board (6).
Turn off power and unsolder one end of
diode CR8 and CR9. Check the
resistance of each diode in one direction
and then reverse leads and test in the
other direction. Resistance should be low
in one direction and high in the other.
(r)Replace diodes CR8 or CR9 if they do not pass
capacitors C 1 (7) and C2 (8) on the
reverse side of the printed circuit board.
Unsolder one end of each capacitor from
the circuit board.
(t) Test capacitors C1 (7) and C2 (8) with a multimeter
(set to read ohms) across the capacitor
being tested and then reverse leads
Connection of the multimeter (set for
ohms) across the capacitor should
immediately result in the movement of the
meter pointer from the infinity 0 side of the
scale to the low ohms side of the scale
and then slowly return to the infinity 0 side
of the scale.
If the capacitor is shorted or leaky, the
pointer will remain on the low ohms side
of the scale. If the capacitor is open,
there will be no movement of the meter
pointer. Replace open, shorted, or leaky
capacitors as required.
Locate zener diode VR3 on circuit board
and apply 115 VAC to terminals #24 and
#27 of the terminal strip TB 1 (5, Figure 7-
Check the voltage across zener diode
VR3. Voltage across VR3 should be
approximately 4.7 VDC.
If voltage across VR3 is greater than 4.7
VDC, replace VR3. If no voltage is
indicated across VR3, locate R3 a 1K
ohm resistor located on circuit board.
Disconnect the 115 VAC power source
from the regulator, unsolder one end of
R3 from the circuit board. Measure the
resistance of R3, resistance should be
between 900 and 1100 ohms. If resistor
is within this range, reconnect lead.
Replace resistor if not within tolerances.
Apply the 115 VAC power to terminals #24
and #27 of the terminal strip TB1 (5).
Recheck the voltage drop across zener
diode VR2, there should be a voltage drop
of 14 VDC present. If 14 VDC is present
and there is no voltage drop across zener
diode VR3, VR3 should be replaced.
If none of the tests or recommended
repairs correct the operation of the voltage
regulator, entire voltage regulator should
7-14.4 Change 8