Chapter 11 553
Synthesizer Section
Unlocked YTO PLL
Troubleshooting an Unlocked YTO PLL
1. If the YTO PLL is unlocked, error code 301 should be displayed.
Place the spectrum analyzer in ZERO SPAN. Figure 11-7 on page
554 illustrates the simplified YTO PLL.
2. Move the jumper on A14J23 to connect pins 2 and 3 (TEST position).
Refer to Figure 11-1 on page 524 for the location of A14J23. Error
code 301 should no longer be displayed. (The YTO PLL feedback
path is now open and the YTO error voltage is forced to zero.)
3. On the spectrum analyzer, press
CAL, MORE 1 OF 2, FREQ DIAGNOSE,
and
LO FREQ. The displayed LO FREQ is the desired YTO frequency
calculated. Record the calculated YTO frequency below:
4. Measure the YTO frequency at the front-panel 1ST LO OUTPUT
jack and record below:
Table 11-5 Amplifier Polarities
YTO Error Sign
Amplifier
ERRSGN
(A14U313 pin 19)
Fractional N Positive Positive TTL High
Oscillator
Swept
Sampler IF
Negative Negative TTL Low
Sampler IF
FM/Main
YTO
Positive Positive TTL High
Coils Swept Sampler IF
Negative Negative TTL Low
Sampler IF
YTO frequency (calculated) =__________________ MHz
YTO frequency (measured) = ___________________MHz
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