Service manual

June 21, 2004 1-37
NP88 FLEX GENERAL
Troubleshooting
8. Check the RF takeover:
a. Apply 1.3 Vdc to the battery contacts.
b. Monitor M1 with ac voltmeter.
c. Tune pageraccordingto“Alignment Procedure” intheapplicable receiver
section.
d. Turn the RF signal generator off and note the noise level at M1.
e. Shortthebase of theRFAmplifierto ground and note thelevel drop. With
a properly functioning RF amplifier, the noise drops 5 to 9 dB, which
indicates the proper amount of gain in the stage.
ExcessiveRFtakeoverindicatestheRFAmplifierisnoisyorregenerative.Low
RF takeover does not always indicate the RF Amplifier is defective. Either too
much or too little gain in any other stage can cause a loss of RF takeover.
9. Check mixer takeover:
a. Ensure the input of the RF Amplifier is still shorted to ground.
b. Short the base of the First Mixer Transistor to ground. The noise level at
M1 must drop 3 to 5 dB. If the noise level drops less than 2 dB, recheck
mixer injection frequency to produce a reference reading of 40 dBm (on
HP400 FL ac voltmeter) at M1.
10. Check system bandwidth:
a. Use the same test setup as in “10 dB Rise Measurement.”
b. Adjust t he RF generator level to the pager’s exact carrier frequency to
produce a reference reading of 6 dB above the receiver noise level at M1.
c. Increase the RF signal generator frequency to produce a 3 dB drop in the
levelatM1. Thesignalgeneratorfrequencymust begreaterthan orequal
to 5 kHz above the carrier frequency.
d. Perform the same measurement below the carrier frequency. The signal
generator frequency must be greater than or equal to 5 kHz below the
carrier frequency. The total bandwidth must not exceed 15 kHz; refer to
Figure 1-32.
.
e. Handle differences a s follows:
• If the difference between f
c
and f
1
or f
2
is less than 5 kHz, or the total
bandwidth is less than 10 kHz or more than 18 kHz, connect an ac
voltmeter to the receiver-specific test point and repeat the bandwidth
measurement.
Figure 1-32. Bandwidth Measurement Detail
FREQUENCY
3 dB
-40 dB
-43 dB
OUTPUT
LEVEL
AT M1
5kHz
MIN
5kHz
MIN
18kHz
MAX
f
1
f
2
f
c