HP 8560A, Service Manual

Page: 409 / 450

7. If a flat line is displayed within 2 of the reference level and the performance test passed,
troubleshoot microcircuits A7, A8, and A13.
8. If a flat line is displayed within 2 of the reference level and the performance test failed,
troubleshoot the Al5 RF Assembly.
Confirming Third Converter Output
1. Connect the HP CAL OUTPUT to INPUT 50
2. Set the HP 8560A to the following settings:
C E N T E R F R E Q
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.
Press
4. Disconnect W29 from
5. Connect a test cable from to the input of another spectrum analyzer.
6. Tune the other spectrum analyzer to 10.7 MHz. The signal displayed on the other
spectrum analyzer should be approximately -5
7. Remove the test cable from and reconnect W29 to
Third Converter
See Function Blocks A, B, C, D, and E of Al5 RF Schematic Diagram (Sheet 2 of 4) in the
component-level information binder.
The 3rd Converter consists of the 2nd IF Distribution, 2nd IF Amplifier, Double
Balanced Mixer, 10.7 MHz Filter, and Flatness Compensation Amplifiers. The 2nd
IF Distribution switches between two possible 2nd IF inputs: the internally generated 2nd IF,
or the external mixing IF INPUT ( non-option 002 analyzers only). A variable dc bias can be
applied to the IF INPUT for external mixers which require such bias. The selected input is
fed to the
2nd IF Amplifier. This is a microcircuit consisting of two stages of gain and
two stages of SAW filters for image frequency rejection.
The 2nd IF Amplifier’s factory-selected attenuator is chosen to achieve a gain from
or
to of 12
The Flatness Compensation Amplifier consists of three fixed-gain stages and two stages of
variable attenuation. This provides an overall adjustable gain of 8
to 32 This gain
is adjusted during an analyzer sweep to compensate for front-end conversion-loss versus
frequency. Perform the following steps to test the amplifier’s gain:
The 10.7 MHz provides a broadband termination to the mixer while filtering
out unwanted mixer products.
1. On the HP
INTERNAL MIXER.
2. In the 2nd IF Distribution (Function Block A), diode CR802 should be forward biased
and diode CR801 should be reverse biased.
RF Section 1 1