Chapter 11 527
Synthesizer Section
Troubleshooting Test Setup
Troubleshooting Test Setup
Some synthesizer section problems require placing the YTO PLL in an
unlocked condition. This is done by moving jumper A14J23 to the TEST
position. This grounds the YTO ERROR signal and disables 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.
Synthesizer section troubleshooting is best done with the spectrum
analyzer 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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