Chapter 10 527
Synthesizer Section
Unlocked Reference PLL (100 MHz VCXO)
• 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 27 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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