HP 8560E, Service Manual

Page: 546 / 665

Chapter 10 545
Synthesizer Section
Unlocked YTO PLL
indicated in the FREQ DIAGNOSE menu will be negative when
locking to lower sidebands. Refer to function blocks E, M, and N of
A14 frequency control schematic in the
Component Level Informatio
n.
Set the HP 8560E/EC to the following settings:
Center frequency .................................................. 300 MHz
Span .............................................................................. 0 Hz
37.Remove jumper A14J23 and connect a dc power supply to A14J23
pin 2. Connect ground to A14J23 pin 3. Set the dc power supply to
+7.5 Vdc.
38.Verify the nominal test-point voltages listed in Table 10-9 on
page 545 .
39.Change the input voltage to
−
7.5 volts and re-verify that the voltages
listed in Table 10-9 on page 545 are the same except for a change in
polarity.
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 10-9 on page 545 .
Check main coil coarse and fine DACs (steps 41-44)
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.
42.Set the HP 8560E/EC to the settings listed below. This sets both
DACs to 128 (the DAC setting range is 0 to 255).
Center frequency .................................................. 300 MHz
Span .............................................................................. 0 Hz
Trigger ......................................................... SINGLE, EXT
(with no external trigger connected)
43.Press
SAVE
,
PWR ON STATE
and turn off the spectrum analyzer.
44.Place jumper A14J23 in the TEST position and turn on the spectrum
analyzer.
Check main coil tune DAC (steps 45-49)
Table 10-9 Voltages in FM Coil and Main Loop Drivers
Measurement Points Voltages
A14U405 pin 6 +2.8 Vdc
A14U322 pin 2 0 Vdc
A14J17 pin 4 >+10 Vdc