TROUBLESHOOTING AND REPAIR
RF LEVEL/AM
PROCEDURE:
R51 is adjusted so that the Premodulator output is 3.5 dBm at 800 MHz. Assuming
that the shape of the control voltage versus frequency curve is typical, this minimizes
the overall variation and thereby minimizes loop gain variation and consequently
minimizes bandwidth variation. C7 is adjusted adjusted to give the optimum level out
of the Premodulator PCA at 1056 MHz.
1. Remove bottom instrument cover and bottom module plate cover.
2. Program the UUT to SPCL 01, 800 MHz, and +7 dBm. Measure the output power
of the Premodulator PCA by disconnecting the cable from J16 on the Premodu-
lator PCA and connecting the power meter. Adjust R51 for 3.5 dBm.
3. Edit the frequency to 1056 MHz and observe the power again. Adjust C7 to obtain
4.5 dBm +.5 dB.
4. Repeat steps 2 through 4.
5. Remove the power meter and move the cable from the output board to J16 on the
Premodulator PCA.
6. Reinstall the bottom module cover and the bottom cover.
Output PCA Q16 Bias Adjustment, R96 6D-21.
The following procedure covers the adjustment of R96 on the Output PCA.
TEST EQUIPMENT:
•
DVM
REMARKS:
This adjustment is required only if Q16 or any associated parts are replaced. This
adjustment sets the bias current in the output transistor for designed operating
conditions.
PROCEDURE:
R96 is adjusted for 1.355V DC between TP1 and TP2.
1. Remove the bottom cover of the instrument, the bottom module cover, and the
pulse cover. This allows access to both the test points and R96.
2. Place the positive (+) lead of the DVM on TP2 and the negative (-) lead on TP1. Set
the DVM to VDC and the 2 volt range.
3. Turn the signal generator on and let it operate for 15 minutes. Program the UUT
with SPCL 01.
4. Adjust R96 until the DVM reads 1.355V DC.
5. Reinstall the pulse cover, the module cover, and the instrument bottom cover.
6D-18
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