532 Chapter10
Synthesizer Section
Unlocked Reference PLL (600 MHz SAWR)
28.If the front panel CAL OUTPUT amplitude is out of specification
and cannot be brought within specification by adjusting A15R561,
CAL AMPTD, check the calibrator AGC amplifier with the following
steps. Refer to function block W of A15 RF schematic.
• Measure the level of 300 MHz at A15 TP505 with an active
probe/spectrum analyzer combination. If the signal is less than +2
dBm, repeat the first 29 steps of this procedure.
• If the signal at this point is correct, place a short across the PIN
diode CR503.
• If the signal level at the CAL OUTPUT is still less than −10 dBm
with CR503 shorted out, troubleshoot the RF forward path
through amplifier Q505. (The signal amplitude decreases.)
• If the CAL OUTPUT signal level is greater than −10 dBm,
troubleshoot the PIN diode attenuator, the detector, or the
feedback path.
29.Measure the detector voltage at A15J502 pin 14. The voltage should
measure approximately +0.3 Vdc when the CAL OUTPUT signal is
at −10 dBm. This voltage should change with adjustment of
A15R561, CAL AMPTD.
30.Check that the voltage at U507A Pin 3 is +1.7 Vdc. If this voltage is
not correct, there may be a problem with the +10 V reference.
31.Measure voltage at U507B pin 5 while adjusting R561. This is the
temperature-compensated adjustable voltage reference to which the
detected voltage is compared. It should vary between +0.15 V and
+0.6 V.
32.Adjust R561 to its limits and verify that the output U507B pin 7
measures approximately +1 Vdc at one limit and −12 Vdc at the
other limit.
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