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) between 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