Chapter 9 483
Controller Section
Display Problems (8560E)
Bad Characters or Graticule
If the displayed characters are bad but the graticule is correct (or if the
symptoms are reversed), troubleshoot the X- and Y- generator switches
A2U207D and A2U207C. Check that the switch driver signal LCHAR is
working properly. Refer to "Display Jumbled or Trace Off Screen" in
this chapter.
Long Lines Dimmer than Short Lines
Refer to function block M of A2 controller schematic diagram (sheet 1 of
4) in the HP 8560 E-Series 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, ∆X, 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 A2U210D-14.
3. Set an oscilloscope to the following settings:
Amplitude scale ......................................................10V/div
Sweep time ............................................................. 1ms/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 on
page 484. 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).
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).
7. Remove the short from J201 pin 13 to ground. Short A2J201 pin 1 to
ground.
To Next Page
Loading...
General
