Input To Main/Fm/Vco Sweep Switch; Settings Of Sweep Switches - HP 8560A Service Manual

3. If A14J17 pin 1 does not appear to be correct, verify that the sweep ramp is reaching the
Change the oscilloscope's amplitude scale to 1.25 V/d'iv and monitor the A14J15 pin 14.
The waveform should be a 0 V to -10 V sweep of 50 ms duration. See Figure 10-7.
Check for a 0 V to -10 V ramp at A14J15 pin 13. Refer to function block H of Al4
Frequency Control Schematic (sheet 2 of 5).
Check that state of the Main/FM/VCO S weep Switches as indicated in Table 10-9.
Note Switches U324A and U318C can change the polarity of A14U404B. This
allows the Roller Oscillator to sweep backwards when the YTO is locked to
a lower sideband of a Sampling Oscillator's comb tooth. The YTO always
sweeps forward (lower frequency to higher frequency), but the Roller Oscillator
sometimes sweeps backwards (higher frequency to lower frequency). The
DIAGNOSE
S o u r c e
P r o b e
X S e l e c t e d
C u r s o r 0
C u r s o r O - X
0 . 0 0 v
0 . 0 0
Switch
menu will indicate a negative Main Roller frequency in this instance.
C h o n 1 1 1
A d j u s t 1 - 2 . 5 0 0 v
1
Figure 10-7. Input to Main/FM/VCO Sweep Switch
Table 10-9. Settings of Sweep Switches
Switch State
Open
Open
Open
Closed
Closed
Closed
A u t o S c a l e
O n E v e n t 0000 1
Cdc 1 Cl
Switch Control Line
1
9
16
1
8
9
Synthesizer Section
FREQ
1
Mnl
Control Line State
High
High
High
High
High
High