TM 9-4910-663-34
Table 2-5. TROUBLESHOOTING (Continued)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
Step 4.
Connect ohmmeter between left calibration jack of TACHOMETER RPM meter M1 (facing meter)
and center terminal of TACHOMETER RPM PULLEY CALIBRATION potentiometer R35. Set
TACHOMETER RPM SELECT switch S36 to CAL PULLEY position and check for zero indication on
ohmmeter. Then, set TACHOMETER RPM SELECT switch S36 to DIRECT DRIVE position, and
check for open circuit indication on ohmmeter.
If either indication is not as specified, replace TACHOMETER RPM SELECT switch S36.
Step 5.
Connect ohmmeter between center terminal of TACHOMETER RPM PULLEY CALIBRATION
potentiometer R35 and terminal 1 of PC board assembly. Set TACHOMETER RPM SELECT switch
S36 to DIRECT DRIVE position, and check that resistance indication on ohmmeter is adjustable over
range of 0 to 100,000 ohms ±10%, using TACHOMETER RPM PULLEY CALIBRATION control.
If resistance indication is not within specified range, replace TACHOMETER RPM PULLEY
CALIBRATION potentiometer R35.
Step 6.
Connect ohmmeter between terminals 1 and 2 of PC board assembly. Set TACHOMETER RPM
SELECT switch S36 to DIRECT DRIVE position. Check for 2740 ohm ±1% indication on ohmmeter.
If resistance is not as specified, replace resistor R33 on PC board assembly.
Step 7.
Connect ohmmeter between center terminal of potentiometer R36 on PC board assembly and
terminal 2 of PC board assembly. Set TACHOMETER RPM SELECT switch S36 to CAL PULLEY
position. Check for 15,000 ohm ±1% indication on ohmmeter.
If resistance is not as specified, replace resistor R34 on PC board assembly.
Step 8.
Connect ohmmeter between terminals 2 and 7 of PC board assembly. Set TACHOMETER RPM
SELECT switch to CAL PULLEY position. Check for indication between 15,000 and 25,000 ohms on
ohmmeter.
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