HP 8560A, Service Manual

Page: 338 / 450

Long Lines Dimmer Than Short Lines
See function block M of A2 Controller Schematic Diagram (sheet 1 of 4) in the
HP Spectrum Analyzer Component Level Information.
The Z Output function block contains the absolute value circuits which determine the
intensity of vectors drawn on the display. The vector length is approximated by the sum of
the X length and Y length. The voltage corresponding to the X length, AX, is converted
to current by R274. If the voltage is negative, it is amplified by 2 in
converted
to current by and added to the current from This effectively turns both
negative and positive voltages into positive currents, hence absolute value.
1.
2.
Short pin 13 to ground
Connect channel A of an oscilloscope to pin 2. Connect channel B to
3.
4.
5.
Set an oscilloscope to the following settings:
Amplitude scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Sweep time
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..External
Externally trigger the oscilloscope off the signal at pin 8 (LBRIGHT).
The waveforms should look like those illustrated in Figure 9-9. If the waveform at
pin 2 is bad, troubleshoot the X Line Generator (function block D of the A2 Controller
Schematic, sheet 1 of 4 in the
HP Spectrum Analyzer Component Level
Information
binder.)
6.
7.
If the waveform at pin 14 is bad, troubleshoot the Z Output circuit (function block
M of A2 Controller Schematic, sheet 1 of 4 in the Component-Level Information binder).
Remove the short from pin 13 to ground. Short pin 1 to ground.
1 0 . 0 0 . 0 0 v 1 . 0 0 0 . 0 0 0
Figure 9-9. Delta X Waveform
8.
Move the oscilloscope’s channel A probe to 5201 pin 14.
S K 1 9 8
Controller Section 9-11