Control Module - HindlePower SCR series Operating Instructions Manual

4. An SCR can also be checked for operation with a Simpson Model 260 voltohmmeter. With the
black lead in common and red lead in +, put polarity switch to + DC. Connect the red lead to the anode
and the black lead to the cathode. The meter should now indicate high resistance above 50,000 ohms
(when on the R x 10,000 scale). With the leads connected as above, set the function switch to R x 1 and
touch the gate to the anode. This should fire the SCR and give a reading of approximately 5-20 ohms. This
shows the SCR has been turned on. On very small SCR's this reading will hold after removing the gate
lead. This is latched-on and can be unlatched by opening the cathode lead. Larger SCR's will not stay on
with the current available with Simpson meter. The Simpson may not have enough current to gate or turn
on extremely large SCR's (400 amp and up).
5. If the charger output is too high, unplug the control module and turn on the charger. With no
gate signals the charger should have zero output. If there is still current output, one or both SCR's are
defective.
6. The above checks can be used to confirm that a suspected SCR is indeed bad. However,
occasionally an SCR might check OK in all these tests and still break down or fail in the charger circuit
during normal operation. Any SCR's suspected should be replaced.
g. Control Module, A1 (PCB Assembly)
One preliminary note that should be kept in mind: The action of the overall feedback circuit
controls the battery charger output voltage so that the feedback voltage from the slider of potentiometer,
R3, "FLOAT ADJ.", to the control module board matches the 6.4 volt reference voltage on the module.
Measure this voltage and if it is not approximately 6.4 volts the feedback circuit or related circuits are not
functioning. Proceed as follows using the GROUND ISOLATED oscilloscope described in Section III, 2,
f, 2 above. Make the following tests in the order shown.
1. If the gate signals were not checked as described in Section III, 2, f, 2 do so at this time. If one or
more of the gate signals are absent when attempting to operate the charger in a normal manner, make the
following checks. (Refer to FIGURE 1 on page 29 for component layout and test point locations on the
trigger board. See schematic on page 30 for related circuit diagram.)
2. Check DC voltages at test points A (+ 10 volts) and B (- 10 volts), referred to board ground,
(GND). If either or both voltages are missing, check fuse F1, transformer T1, and diodes CR1 through
CR4 on the PCB for malfunction. If ok, proceed as follows.
3. The following waveform tests must be made using the oscilloscope set with vertical sensitivity
set at 2V/CM and the horizontal time base set at 5MS/CM. Compare the waveforms observed with those
shown in FIGURE 2 on page 31 for the various test points indicated.
4. Check waveform at test point C and compare with FIGURE 2. If improper waveform check
CR12 and CR13. Check amplified inverted waveform at test point D. If not present, replace IC2.
5. Check ramp pattern at test point E. If not proper, replace Q1 only with its own type, Motorola
MPSA55. Do not substitute.
6. Check the ramp with floating DC reference at test point F. If not present, replace IC2.
7. Check the short pulse at point G. If not present, check unijunction transistor Q3.
8. Check waveform at point H. Note that at both points G and H, there may be multiple pulses
instead of only one pulse per 8.33ms. period. This is normal particularly if the unit is calling for maximum
output voltage. If no pulse waveform is present replace transistor Q2.
9. Check the battery charger rectified waveform by connecting the oscilloscope across the bleeder
resistor, R1, and readjusting the input sensitivity to 20V/CM. If the unit is turned "half-on", the waveform
will look approximately like the waveform of I of FIGURE 2.
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