Service manual

1-38 June 21, 2004
GENERAL NP88 FLEX
Troubleshooting
• If the bandwidth is still outside the prescribed limits , replace the IF
Crystal Filter.
• If the bandwidth is within the prescribed limits, replace the Ceramic
IF Filter (Discovery I receivers).
• If testing a Discovery II receiver or if the bandwidth is still outside
the prescribed limits, replace the Backend Demodulation IC on the
receiver circuit board.
11. Check data filter cutoff frequency:
a. Connect the output of the function generator (set for a 50 Hz sinewave,
1 V peak) to the external modulation input of the signal generator.
b. Set the generator to the pager’s carrier frequency with the following
deviation.
FLEX
±4.8 kHz
c. Measure the output at the receiver-specific test point on the Backend
Demodulation IC with a 1:1 probe connected to the ac voltmeter.
d. Adjust the generator level until the reading on the ac voltmeter is 6 dB
above the noise level output.
e. Slowly increase the frequency of the function generator until the reading
on the ac voltmeter decreases 3 dB. The frequency at the function gener-
ator must be within the following applicable range:
FLEX
2400 Hz ±20%, 6400 bps
Backend Filter Measurement
1. Ensure a battery with a minimum output of 1.3 volts is installed in the pager.
2. Refer to Tables 1-9 and 1-10 for lists of recommended test equipment.
3. Refer to the applicable schematic waveform and voltage information in the
appropriate supplement.
4. Ensure the pager is in self-diagnostic mode 5 (refer to "Self-Diagnostic Fea-
ture").
5. Install the alignment back cover on the pager.
6. Place the unit in theRTL-1005 RadiationTestFixture,modifiedwiththe RPX-
4687 Nest and Contact Flip-down Assembly.
7. Set up the test equipment.
8. Set the RF generator to the customer frequency:
a. Apply an unmodulated signal.
b. Adjust its amplitude so the reading is 5 dB below the full comprehension
level.
9. Check the frequency above and below the customer frequency:
a. Offset the frequency 4.5 kHz above the customer frequency. Note the
reading (VdB1).
b. Offset the frequency 4.5 kHz below the customer frequency. Note the
reading (VdB2).
c. Reposition the RF generator frequency to the customer frequency.
10. Determine if the backend is properly aligned (Is | VdB1 - VdB2 | <=1.5dB)