HP 8560A Service Manual

Caution
Using an active probe, such as an HP 85024A, with a spectrum analyzer is
recommended for troubleshooting the RF circuitry. If an HP 1120A Active
Probe is being used with a spectrum analyzer, such as the HP 8566A/B,
HP 8569A/B and the HP 8562A/B, having dc coupled inputs, either set
the active probe for an ac coupled output or use a dc blocking capacitor
(HP 11240B) b t
e ween
the active probe and the spectrum-analyzer input.
Confirming a Faulty Synthesizer Section
The All YTO (the HP 8560A’s first LO)
is a Yig-Tuned Oscillator which tunes from 2.95
to 6.8107
GHz. The A7 1ST LO Distribution Amplifier (LODA) levels All’s output and
distributes the signal to the A8 Low Band Mixer, A15A2 Sampler, and the front panel’s 1ST
LO OUTPUT. The Synthesizer Section includes the following PLLs (Phase Locked Loops):
YTO PLL
A7, All, Al4 and Al5 RF assembly
Offset PLL (Sampling Oscillator PLL) Al5 RF assembly
Roller Oscillator PLL
Al4 Frequency Control assembly
Reference PLL Al5 RF assembly
In addition, the Al4 assembly’s Roller Oscillator PLL is actually comprised of the following
three PLLs:
Main Oscillator PLL
Transfer Oscillator PLL
Offset Oscillator PLL (This is not the same as
A15’s Offset PLL)
The Main Oscillator PLL is sometimes swept backwards (higher frequency to lower
frequency). This is necessary because of the way in which the Sampler IF signal is produced.
Note
The Frequency Control board is mostly digitally controlled. If multiple failures
appear in unrelated areas of the circuitry, the control may be at fault. Refer
to the troubleshooting procedures in this chapter for further help on isolating
those failures.
Note
The TAM is unable to test the signal path on the RF board. It tests the
circuitry by digitally controlling the hardware and monitoring the control lines
to make sure they are responding properly. Use the TAM’s Automatic Fault
Isolation routine or verify the RF levels manually to ensure proper operation.
1. Connect a
DVM’s positive lead to A15J502 pin 3 and the negative lead to A15J502 pin 6.
This measures the reference oscillator tune voltage which is an input to the A3 Interface
assembly’s ADC MUX.
10-2 Synthesizer Section

HP 8560A Specifications

General

Brand	HP
Model	8560A
Category	Measuring Instruments
Language	English