Third Lo Driver Amplifier (100 Mhz Vcxo) - HP 8560E Service Manual

Synthesizer Section
Unlocked Reference PLL (100 MHz VCXO)
Third LO Driver Amplifier (100 MHz VCXO)
The third LO driver amplifier (Q503) amplifies the 300 MHz from the
300 MHz distribution amplifier to a sufficient level to drive the LO port
of the double balanced mixer. During the SIG ID operation, diodes
CR501 and CR502 turn off the 3rd LO driver amplifier in order to
minimize the amount of 300 MHz going to the double-balanced mixer.
Check level at 1. Press
amplifier input
(steps 1-6)
2. Use an active-probe/spectrum-analyzer combination to confirm the
A15X602 pin 5
A15TP504
3. If the signal at A15X602 pin 5 is low, but the signal at A15TP504 is
4. Check that PIN diode switches CR603 and CR605 are reverse biased
5. Measure 300 MHz signal at A15TP503 using an active
6. If the level at the TP503 is correct, but signal at TP504 is too low, the
528
,
AUX CTRL INTERNAL MIXER
installed.
power level of the 300 MHz signal at the following test points:
correct, press
AUX CTRL
, if present.
OFF
by approximately +10 Vdc. Refer to function block F of A15 RF
schematic.
probe/spectrum analyzer combination. If the signal is not
approximately +10 dBm, refer to "Unlocked Reference PLL (100
MHz VCXO)" in this chapter.
fault is probably in the amplifier.
. Press
SIG ID OFF
≥+7 dBm
≥+15 dBm
, . Press
INTERNAL MIXER
, if option 008 is
SIG ID
Chapter 10