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
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
7.Remove the short from J201 pin 13 to ground. Short A2J201 pin 1 to ground.
1 0 . 0 V/div | 0 . 0 0 v | 1 . 0 0 ms/div | 0 . 0 0 0 s |
S K 1 9 8
Figure
8.Move the oscilloscope’s channel A probe to 5201 pin 14.
Controller Section