TROUBLESHOOTING AND REPAIR
FREQUENCY AND PHASE MODULATION
7. Set the UUT to SPCL 909. Connect a 50-ohm termination to UUT EXT PULSE
MOD. Connect the 8840A to J4-P5. The 8840A should read 0V DC ± .2V DC.
Press the External Pulse Modulation button on UUT front panel to on. The 8840A
should read 4.2V DC ± .2V DC.
8. Set the UUT to SPCL 909. Set the 8840A to DC volts, 2-volt range. Connect the
8840A to TP1 on the 4048 board. Adjust the modulation level sense R71 for .98V ±
.5 mV. Remove 8840A from TP1.
9. Set the UUT to EXT FM. Set the 6011A to 1 kHz and 383 mV. Connect the 6011A
and the 8840A to the UUT FM EXT input.
a. Edit the 6011A level until the 8840A reads .707V RMS. Verify on the UUT
front panel that the EXT FM LO and the FM HI annunciators are off.
b. Increase the 6011A output voltage to .728V RMS as measured on the 8840A.
Verify that the EXT FM HI annunciator is on.
c. Decrease the 6011A output voltage to .685V RMS as measured on the 8840A.
Verify that the EXT FM LO annunciator is on.
10. Set UUT to SPCL 909, EXT AM. Set the 6011A to 1 kHz and 383 mV. Connect the
6011A and the 8840A to the UUT AM EXT input.
a. Edit the 6011A level until the 8840A reads .707V RMS. Verify on the UUT
front panel that the EXT AM LO and the AM HI annunciators are off.
b. Increase the 6011A output voltage to .728V RMS as measured on the 8840A.
Verify that the EXT AM HI annunciator is on.
c. Decrease the 6011A output voltage to .685V RMS as measured on the 8840A.
Verify that the EXT AM LO annunciator is on.
Alignment of FM PCA (A14) 6E-18.
Align the FM PCA as described in the following procedure:
1. Center all pots on the FM PCA. Turn the UUT off. Set the 6011A to 50 kHz at 0
dbm. Connect the 6011A to TP12. Connect the spectrum analyzer to TP11. Adjust
L6 for a minimum 50-kHz level. Remove the 6011A and the analyzer.
2. Set the UUT to SPCL 909, 800 MHz, 62.5-kHz dev, 1-kHz mod rate, INT ACFM.
Set the 8840A to AC volts, autorange. Connect the 8840A to TP1 on the FM PCA.
Adjust R107 for 2.828V RMS ± 2 mV RMS. Turn INT ACFM off.
3. Remove the cap from J3 to J17 connecting the FM PCA to the Sum Loop PCA
(A12). Connect the counter to J3. Adjust L1 to be flush to the top of its housing.
Adjust C9 for a locked 80 MHz as read on the counter.
4. Remove the counter from J3 and connect 436A to J3. Adjust R45 for -5 dBm ± . 1
dB. Disconnect 436A from J3. Install the 1000 pF cap from J3 to J17 on the Sum
Loop PCA.
5. Connect the 8840A to TP9. Set the 8840A to DC volts. Adjust R44 for 0V DC ± 10
mV DC.
6E-14
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