TB-9-2920-225-34-1
100 AMP REGULATOR
TECHNICAL BULLETIN; CHECKOUT AND REPAIR PROCEDURES
NOVEMBER 1981
TB-9-2920-225-34-1 - Page 48 of 70
TB 9-2920-225-34-1
Figure 3-9. Open view-mode 5027 RC.
(2) Place ohmmeter probes to the terminals
of the rheostat (see figs. 3-9,3-10, and 3-11).
(3) Rotate rheostat fully clockwise; reading
should be approximately 45 ohms.
(4) Rotate rheostat fully counterclockwise,
reading should be less than 5 ohms.
(5) If other readings are obtained, replace
the rheostat.
d. Power Resistor R2.
Place ohmmeter probes
across power resistor R2 (see figs. 3-9, 3–10, and
3-11). Meter should read approximately 30 ohms.
e. Detailed Circuit Checks.
(1) Table 3-4 contains “power off” resistance
checks of the circuit (see figs. 3–9, 3–10, and 3–11
for test points).
(2) Table 3-4 contains
“power on”
voltage
checks of the circuit (see figs. 3-9, 3-10, and 3-11
for test points ).
NOTE
Power transistors on the circuit board
and heat sink can be checked as outlined
on figures 3–1 and 3–2. However, since
they are soldered into the circuit, re-
moval and replacement is more time con-
suming.
f. Functional Check.
Check the performance of
the regulator on the test stand and make final
voltage adjustments. Voltage output should read
28 volts. If the regulator does not function prop-
erly, perform the following:
(1)
(2)
(3)
Check wires and connections.
Replace circuit board or cover assembly.
Perform bench test procedures.
NOTE
After final repair, check regulator on the
test stand.
If the regulator still does not function correctly
it will be necessary, if local skills permit, to test
each component. All the parts should be checked
with an ohmmeter and the capacitors checked with
a capacitance meter. The circuit board traces
should rechecked with an ohmmeter to make sure
that there are no cracked traces. Traces with hair-
line cracks will show good at lower temperatures
and will tend to show open circuit at higher tem-
peratures. If the board seems good at room tem-
perature, but the regulator still fails, this could
be the cause.
3-11
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