Display Jumbled Or Trace Off Screen; Expanded Blanking Waveforms - HP 8560A Service Manual

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Display Jumbled or Trace Off Screen

See function blocks D and I of A2 Controller Schematic Diagram (sheet 1 of 4) in the
Component-Level Information binder.
The two line generators are identical circuits, so the following steps apply to both; references
will be to the X generator with Y references in parentheses.
1. The voltage at A2U202B pin 7 should measure 10.0 V.
2. Perform steps 1 through 5 of "Line Generators" in this chapter. If the X POS and Y POS
waveforms look different from those illustrated in Figure 9-2, check the waveforms at the
low-pass filter's input (function block E).
3. The waveform at the low-pass filter should look like X POS in Figure 9-2 but have an
amplitude from 0 V to +5 V.
4. If the waveform in step 3 is incorrect, set an oscilloscope to the following settings:
Amplitude Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 V/div
Sweep Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20ps/div
Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..External
5. Trigger the oscilloscope on the signal at U207 pin 8 (LBRIGHT).
6. Compare the line-generator input signals at the following test points with those illustrated
in Figure 9-5. INTEGRATE and SAMPLE waveforms are replicas of VECTOR except for
polarity and amplitude. LCHAR is low when characters are drawn.
INTEGRATE: Q202's collector
SAMPLE:
LCHAR:
VECTOR:
4 . 0 0
2 . 5 0 V
I L
Figure 9-4. Expanded Blanking Waveforms
U213 Pin 9
2 . 0 9 6 . 0 0 u s
Controller Section 9-7
S K 1 9 3