Giga-tronics GT 9000, Руководство по эксплуатации и техническому обслуживанию

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5.3.8 Output Phase Lock Loop
This circuit is located on the A18 PC board.
Corrective Action
1. Verify that the coarse tuning of the YIG is not pushing the frequency out of the control
range of the PLL. Remove the A18 board, and check the RF output with a frequency
counter; it should be within 10 MHz of the requested frequency. If not:
2. Check the YIG driver circuit (see Section 5.3.10).
3. Check the YIG oscillator (see Section 5.3.4).
4. Verify that an appropriate input from the divide-by-N circuit (see A17) is being received.
5. The output from the FM drivers (U20 - U22) goes more negative to increase the YIG
output frequency, more positive to decrease frequency; be sure that the PLL output is
not driving the YIG oscillator in the wrong direction.
6. Verify continuity between the output of the PLL circuit (there are separate outputs for
different frequency ranges) and the YIG FM- input pin.
7. If possible, replace the circuit with a spare.
5.3.9 Divide-By-N
This circuit is one half of the frequency divider PC board (A17).
Corrective Action
Verify that the circuit is being programmed with the correct divisor, by checking the inputs to the logic
level translator ICs at the frequencies listed in Table 5-5 (the inputs to these ICs are at TTL levels).
Bit IC/pin
Expected Logic Levels
@ 10.000 GHz @ 10.161 GHz @ 10.001 GHz
(see note)
@ 10.033 GHz
(see note)
0 U3-5 H L
1 U3-10 H L
2 U3-7 H L
3 U2-11 H L
4 U2-10 H L
5 U2-7 L L H
6 U2-5 H L
7 U1-7 L L H
8 U1-5 L H
Bits 0 through 8 are tested for different output frequencies to verify that they toggle as expected. Frequencies of 10.000 and
10.161 GHz are sufficient to test all but two of these bits. Bits 5 and 7 do not toggle between those two frequencies, and must be
checked at 10.001 and 10.033 GHz, respectively (otherwise the latter frequencies are not needed for this test). If possible, replace the
circuit with a spare.
Table 5-5. Logic Level Inputs
Model GT 9000 Microwave Synthesizer
5-12
Manual No. 120AM00250, Rev C, September 1998