Long Lines Dimmer Than Short Lines; Delta X Waveform - HP 8560A Service Manual

Long Lines Dimmer Than Short Lines

See function block M of A2 Controller Schematic Diagram (sheet 1 of 4) in the
HP 856OA/61B/63A 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 A2U210C, converted
to current by A2R246, and added to the current from A2R274. This effectively turns both
negative and positive voltages into positive currents, hence absolute value.
1. Short A2J201 pin 13 to ground (A2TP3).
2.
Connect channel A of an oscilloscope to A2J201 pin 2. Connect channel B to
3.
Set an oscilloscope to the following settings:
Amplitude scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 V/div
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 ms/div
Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..External
4.
Externally trigger the oscilloscope off the signal at A2U207 pin 8 (LBRIGHT).
5.
The waveforms should look like those illustrated in Figure 9-9. If the waveform at J201
pin 2 is bad, troubleshoot the X Line Generator (function block D of the A2 Controller
Schematic, sheet 1 of 4 in the
Information
binder.)
6.
If the waveform at U210D 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).
7.
Remove the short from J201 pin 13 to ground. Short A2J201 pin 1 to ground.
8.
Move the oscilloscope's channel A probe to 5201 pin 14.
HP 856OA/61B/63A
1 0 . 0 V/div 0 . 0 0 v
Figure 9-9. Delta X Waveform
Spectrum Analyzer Component Level
1 . 0 0 ms/div 0 . 0 0 0 s
Controller Section 9-11
S K 1 9 8