2. Service
Assembly/Module Diagnostic Trees (Diagnostic Section 3)
116
A18 Diagnostic Tree
(A/M Subsection 8)
This subsection describes the A18 9.2 GHz PLL Module diagnostic tree.
3.8.1.0 A18 Module Power Check
1 Check the +12V, -12V, and +5V terminals on A18 with a DMM.
2 Verify +12V is between +12 and +12.5V to chassis.
3 Verify +5V is between 5.25 and 5.5V to chassis.
4 Verify -12V is between -12V and -12.5V to chassis.
QUESTION: Are power supply voltages correct?
If Yes: Go to, 3.8.2.0.
If No: Go to, 2.1.1.1.0 (Power-supply diagnostic tree).
3.8.2.0 A5 87.368230 MHz Input Signal Test
1 Disconnect coax cable from A18J1.
2 Connect free end of coax to the 50 input of an oscilloscope.
(If a 50 input is absent, use the high-impedance input with a
50 coaxial-feedthrough terminator at the scope end of the coax).
3 Verify the presence of an ~87 MHz sine wave with at least 0.4 Vp-p
amplitude.
4 Reconnect free end of coax to frequency counter input and verify that
signal frequency is 87.368 1 kHz.
5 Reconnect cable to A18J1.
QUESTION: Does the signal comply with the characteristics
described in step 3 and 4?
If Yes: Go to, 3.8.3.0.
If No: Go to, 3.8.2.1.
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