13. If the Transfer Oscillator drive signal is not present, check the XFER AMP BIAS at J303
pin 3. The voltage should measure
+2
Vdc to
+4
Vdc.
14. Check that the voltage at
U424B
pin 7 is nominally -14 Vdc. Diodes CR302 and CR303
form a PIN diode switch that turns off the Transfer Oscillator drive to the mixer in Main
Roller Spans (100 kHz <LO Span
51
MHz). Refer to function block AI of Al4 Frequency
Control Schematic (sheet 5 of 5).
15. Check that control signal XFEROSCSW is near 0 V (U424B pin 5). If XFEROSCSW is
not near 0 V, check the Roller Interface Latch
U401
and its address decoder
U303.
Refer
to function block AG of Al4 Frequency Control Schematic (sheet 5 of 5) and function
block B of Al4 Frequency Control Schematic (sheet 2 of 5).
16. If the signal amplitude at
U109
pin 1 (refer to step 11) is within range and near 2 MHz
in frequency, measure the signal with an oscilloscope at
U109
pin 7. The voltage should
nominally be 100
mVp-p.
17. The waveform at
U106
pin 7 should be a square wave with a lower limit between 0 V and
to.5
V and an upper limit between
+3
V and
+5
V. Refer to function block AL of Al4
Frequency Control Schematic (sheet 5 of 5).
18. The signal at
U105
pin 1 should have a similar waveform as
U106
pin 7, but may be
different in amplitude from the Offset Oscillator Dividers
U103
and
U104.
19. The Offset Oscillator Divider, function block AJ, is probably at fault if the signal at
U105
pin 1 is not present and the Offset Roller is locked.
20. If the input signals to the Main Roller Phase Detector
U105
(measured in steps 17 and
18) are in range, check for narrow
(<O.l
ps) pulses 0.5 ps apart on
U105
pins 2 and 13.
21. Short
U115B
pin 5 to ground and check that U115B pin 7 is nominally -9.1 Vdc.
22. Short
U115B
pin 6 to ground and check that U115B pin 7 is nominally +9.1 Vdc.
23. If ERR 304 is displayed and the Main Oscillator PLL is locked, troubleshoot Roller MUX
U305,
MUX Amp U328, and MUX Gain Control Switch U326B. Refer to function block
AG in Al4 Frequency Control Schematic (sheet 5 of 5).
24. If
U305,
U328, and U326B are working properly, suspect a malfunction of the A3 Interface
Assembly or the W2 Control Cable.
25. Remove the jumpers.
lo-36
Synthesizer Section
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