508 Chapter10
Synthesizer Section
Synthesizer Troubleshooting Section
Synthesizer Troubleshooting Section
The A11 YTO (the HP 8560E/EC first LO) is a YIG-tuned oscillator
which tunes from 2.95 to 6.8107 GHz. The A7 LO distribution amplifier
(LODA) levels the output of A11 and distributes the signal to the A8
low band mixer, A10 YIG-tuned mixer/filter, A15U100 sampler, and the
1ST LO OUTPUT on the front panel. The synthesizer section includes
the following PLLs (Phase Locked Loops):
The fractional N 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 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.
The TAM tests the signal path circuitry by digitally controlling the
hardware and monitoring the control lines to make sure they are
responding properly. Use the TAM automatic fault isolation routine or
verify the RF levels manually to ensure proper operation.
Check A3 ADC MUX function block (steps 1-4)
1. Connect positive lead of a DVM to A15J200 pin 13, and the negative
lead to A15J200 pin 6. This measures the sampling oscillator tune
voltage, which is an input to the ADC MUX of the A3 interface
assembly.
2. Set the HP 8560E/EC to the following settings:
Span .................................................................................0Hz
Center frequency .................................................. 389.5MHz
Trigger .......................................................................... Single
3. Use the data entry keys to tune the
CENTER FREQ to the values
listed in Table 10-1 on page 509.
YTO PLL A7, A11, A14 and A15 assemblies
Offset PLL (sampling oscillator
PLL)
A15 RF assembly
Fractional N PLL A14 frequency control assembly
Reference PLL A15 RF assembly
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