514 Chapter10
Synthesizer Section
Test Setup Troubleshooting
Test Setup Troubleshooting
Some synthesizer section problems require placing the YTO PLL in an
unlocked condition. Do this by moving jumper A14J23 to the TEST
position. This grounds the YTO ERROR signal and stops the CPU from
detecting an unlocked YTO. The FM coil driver output is set to its
mid-range level causing the YTO to be controlled only by the main coil
tune DAC.
It is best to troubleshoot the synthesizer section with the HP 8560E/EC
span set to 0 Hz (even though it is still possible to sweep the Main and
FM coils of the YTO).
With the YTO in its unlocked conditions and the span set to 0 Hz, the
nominal YTO frequency is not necessarily the value listed as LO FREQ
in the Frequency Diagnose menu. The YTO has an initial pretune
accuracy of ±20 MHz. To display the nominal YTO frequency, press
CAL,
MORE 1 OF 2, FREQ DIAGNOSE, LO FREQ.
The fractional N oscillator frequency is the same as the desired sampler
IF. To display the fractional N oscillator frequency press CAL, MORE 1
OF 2, FREQ DIAGNOSE, FRAC N FREQ. If the sampler IF is negative
(YTO frequency is lower than the desired sampling oscillator
harmonic), the fractional N frequency will be displayed as a negative
number.
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