(k) Connect a multimeter (set to read 0-
(s) Locate capacitors C1 (7) and C2 (8) on
50 VDC) across points "A" and "B" as indicated on
the reverse side of the printed circuit board. Unsolder
wiring schematic. Connect red lead to point "A" and
one end of each capacitor from the circuit board.
black lead to point "B".
(t) Test capacitors C1 (7) and C2 (8) with
(l) A DC voltage of 28-32 volts should be
a multimeter (set to read ohms) across the capacitor
indicated. If voltage is not within this range, check the
being tested and then reverse leads across capacitor.
voltage across voltage regulating (zener) diode VR1
and VR2 on circuit board.
(u) Connection of the multimeter (set for
ohms) across the capacitor should immediately result
in the movement of the meter pointer from the infinity
(oo) side of the scale to the low ohms side of the scale
If either zener diode VR1 and VR2 is
and then slowly return to the infinity (oo) side of the
removed, do not apply the 115 VAC source to
the regulator until a replacement is con-
nected into the circuit. Failure of the voltage
(v) If the capacitor is shorted or leaky, the
regulator will occur if this caution is not
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
(m) The voltage across VR1 and VR2
capacitors as required.
should be approximately 14 VDC. Replace zener
diodes that do not have a voltage drop of approxi-
(w) Locate zener diode VR3 on circuit
board and apply 115 VAC to terminals #24 and #27 of
mately 14 VDC.
(n) After replacing zener diodes VR1
and/or VR2 and no voltage is indicated across either
(x) Check the voltage across zener diode
VR3. Voltage across VR3 should be approximately 4.7
or both zener diodes VR1 and VR2, check the voltage
across terminal lugs #7 and #8 of the T1 power trans-
(y) 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) on circuit
(z) Disconnect the 115 VAC power
source from the regulator. Unsolder one end of R3
(o) A voltage of 25-35 VAC should be
from the circuit board. Measure the resistance of R3.
present. If voltage is not present, check that 115 VAC
Resistance should be between 900 and 1100 ohms. If
power source is connected properly and all wiring con-
resistor is within this range, reconnect lead. Replace
nections to T1 (6) are tight. If power is properly con-
resistor if not within tolerances.
T1 (6) should be replaced.
(aa) Apply the 115 VAC power to termi-
nals #24 and #27 of the terminal strip TB1 (5).
(p) After verifying that 25-35 VAC is
Recheck the voltage drop across zener diode VR2,
present across T1 (6) terminals #7 and #8, locate
there should be a voltage drop of 14 VDC present. If
diodes CR8 and CR9 on circuit board (6).
14 VDC is present and there is no voltage drop across
zener diode VR3, VR3 should be replaced.
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
(bb) If none of the tests or recommended
repairs correct the operation of the voltage regulator,
in the other direction. Resistance should be low in one
entire voltage regulator should be replaced.
direction and high in the other.
(r) Replace diodes CR8 or CR9 if they do
not pass resistance check.