Figure 3-9. Open view-mode 5027 RC.

TB 9-2920-225-34-1

Figure 3-9. Open view-mode 5027 RC.

f. Functional Check. Check the performance of

(2) Place ohmmeter probes to the terminals

the regulator on the test stand and make final

of the rheostat (see figs. 3-9,3-10, and 3-11).

voltage adjustments. Voltage output should read

(3) Rotate rheostat fully clockwise; reading

28 volts. If the regulator does not function prop-

should be approximately 45 ohms.

erly, perform the following:

(4) Rotate rheostat fully counterclockwise,

reading should be less than 5 ohms.

(1) Check wires and connections.

(5) If other readings are obtained, replace

(2) Replace circuit board or cover assembly.

the rheostat.

(3) Perform bench test procedures.

d. Power Resistor R2. Place ohmmeter probes

across power resistor R2 (see figs. 3-9, 310, and

NOTE

3-11). Meter should read approximately 30 ohms.

e. Detailed Circuit Checks.

After final repair, check regulator on the

(1) Table 3-4 contains "power off" resistance

test stand.

checks of the circuit (see figs. 39, 310, and 311

If the regulator still does not function correctly

for test points).

it will be necessary, if local skills permit, to test

(2) Table 3-4 contains "power on" voltage

each component. All the parts should be checked

checks of the circuit (see figs. 3-9, 3-10, and 3-11

with an ohmmeter and the capacitors checked with

for test points ).

a capacitance meter. The circuit board traces

NOTE

should rechecked with an ohmmeter to make sure

that there are no cracked traces. Traces with hair-

Power transistors on the circuit board

line cracks will show good at lower temperatures

and heat sink can be checked as outlined

and will tend to show open circuit at higher tem-

on figures 31 and 32. However, since

peratures. If the board seems good at room tem-

they are soldered into the circuit, re-

perature, but the regulator still fails, this could

moval and replacement is more time con-

be the cause.

suming.

3-11