Table 4-3. Monitor Receiver Troubleshooting-Continued

TM 11-5825-270-23

Table 4- Monitor Receiver Troubleshooting-Continued

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

12.

AURAL ALARM DOES NOT SILENCE

Step 1. Set the POWER switch to OFF. Check the resistance to ground from XA2-15 (fig. FO-3) with ALARM SIL switch S2

pressed. The reading will be 0 ohm.

a. If correct go to table 4-2 and recheck fault indications.

b. If not correct cheek ALARM SIL switch S2 and the associated wiring (fig. FO-3.

13.

ALARM INDICATION

Step 1. Check the CARRIER LEVEL meter reading. The reading will be 0 dB.

a. If correct go to step 3.

b. If not correct go to step 2.

Step 2. Set the POWER switch to OFF. Measure the resistance to ground from A3TP1 (fig. 2-1). The resistance will be an open

circuit.

a. If correct, set the POWER switch to ON and go to step 5.

b. If not correct check the wiring associated with ALARM TEST switch S3 (fig. FO-3).

Step 3. Check the voltage at A2TP3 (fig. 2-1). The voltage will be 0 Vdc.

a. If correct go to step 4.

b. If not correct replace if amplifier assembly A2 (para 4-16).

Step 4. Check the voltage at A4TB1-1. The voltage will be +28 Vdc.

a. If correct replace relay K1 after checking the wiring from A4TB1-1 to K1-6 (fig. FO-3). Replacing K1 requires

direct support maintenance personnel (refer to chapter 5).

b. If not correct go to malfunction 3.

Step 5. Check the voltage at A4TB1-3. The voltage will be +12 Vdc.

a. If correct go to step 6.

b. If not correct go to malfunction 3.

Step 6. Check the waveform at A2TP4 (fig. 2-1) using the oscilloscope. The waveform will be 4 V p-p (fig. 4-1).

a. If correct check the wiring between A2-10 and meter M1 (fig. FO-3).

b. If not correct go to step 7.

Step 7. Check the waveform at A3TP2 (fig. 2-1) using the oscilloscope. The waveform will be 5 V p-p (fig. 4-1).

a. If correct go to step 8.

b. If not correct replace rf amplifier assembly A3 (para 4-16).

CAUTION

When connecting signal generator to J1 of the monitor receiver, connect a 1uF 25 V

capacitor in series with the signal generator output. Make sure that positive side of the

capacitor is connected to J1.

Step 8. Disconnect the antenna from J1. Connect the signal generator to J1. Set the signal generator to the receiver frequency,

with 1 kHz modulation and a 100 mV output. Go to step 9.

Step 9. Set the RF ATTEN switch to 0 and rotate SENSITIVITY control A3R7 (fig. 2-1) fully clockwise. Go to step 10.

Step 10. Check the waveform at TP1 of the switch bracket (fig. 2-1) using the oscilloscope. The waveform will be 0.4 V p-p (fig.

4-1).

a. If correct go to step 11.

b. If not correct check all wiring between TP1 and J1; replace the switch bracket if necessary. This procedure

requires direct support maintenance personnel (refer to chapter 5).

Step 11. Check the waveform at A3TP1 (fig. 2-1) using the oscilloscope. The waveform will be 0.3 V p-p (fig. 4-1).

a. If correct go to step 12.

b. If not correct rotate RF TUNE control to obtain the correct waveform.

(1) If the waveform at A3TP1 is correct perform the procedures of paragraph 2-4.

(2) If not correct replace the switch bracket. This procedure requires direct support maintenance personnel (refer

to chapter 5).

Step 12. Set the RF ATTEN control to 40. Go to step 13.

Step 13. Check the waveforms at A3TP3 and A2TP1 (fig. 2-1) using the oscilloscope. Refer to figure 4-1 for waveforms.

a. If both waveforms are correct replace if. amplifier assembly A2 (para 4-16).

b. If the waveform at A3TP3 is correct and the waveform at A2TP1 is not correct check the wiring between A2-17

and A3-1 (fig. FO-1)

c. If both waveforms are not correct replace if. amplifier assembly A2 (para 4-16).

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