558 Chapter11
Synthesizer Section
Unlocked YTO PLL
40.Change the CENTER FREQ to 678.8 MHz with the SPAN remaining
0 Hz. This will change the switch setting of U326A and invert the
voltages listed in Table 11-6 on page 558.
Check main coil
coarse and fine
DACs (steps
41-46)
41.The main coil coarse and fine DACs correct any initial pretune
errors in the YTO main coil. The DACs adjust the FM-coil current to
zero before any sweep begins. Refer to function block J of A14
frequency control schematic (sheet 2 of 5).
42.Set the spectrum analyzer to the settings listed below. This sets both
DACs to 128 (the DAC setting range is 0 to 255).
Center frequency.................................................. 300MHz
Span ..............................................................................0Hz
Trigger ......................................................... SINGLE,EXT
(with no external trigger connected)
43.Press
SAVE, PWR ON STATE and turn off the spectrum analyzer.
44.Place A14J23 jumper in the TEST position and turn on the spectrum
analyzer.
45.Verify the voltages listed in Table 11-7 on page 558.
46.Place A14J23 jumper in the NORMAL position.
Check main coil
tune DAC (steps
47-49)
47.Set the spectrum analyzer to the following settings:
Center frequency ........................................................ 300MHz
Span ....................................................................................0Hz
48.Place A14J23 jumper in the TEST position.
Table 11-6 Voltages in FM Coil and Main Loop Drivers
Measurement Points Voltages
A14U405 pin 6 +3.116 Vdc
A14U322 pin 2 approx. +1.5 Vdc
A14J17 pin 4 >+10 Vdc
Table 11-7 Main Coil Coarse and Fine DACs Voltages
Measurement Points Voltages
A14J17 pin 2 −5 Vdc
A14J17 pin 3 −5 Vdc
A14J17 pin 5 +5 Vdc
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