Switch Driver Waveform Lchar - HP 8560A Service Manual

I N T E G R A T E
S A M P L E
L C H A R
V E C T O R
7. All of the DAC inputs should change state two or more times within a 5 ms window. If
one or more DAC bits are not working correctly, this will effect the entire display, but
especially in the diagonal lines that go from lower left to upper right. When these lines
are drawn, both the X and Y DACs are stepped one count at a time. A "stuck" bit will
distort the diagonal in a repetitive manner. The quicker the repetition, the less significant
the "stuck" bit. Horizontal distortions apply to the X LINE GENERATOR DAC, while
vertical distortions apply to the Y LINE GENERATOR DAC. The DACS have current
outputs so they are not readily observable with an oscilloscope. Continue with step 8 to
observe the DAC outputs.
8. To break the effect of feedback in the line generators and to observe the output of the
9. Set an oscilloscope to the following settings:
Amplitude Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 V/div
Sweep Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .l ms/div
Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..AC
Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . External
10. Trigger the oscilloscope on the signal at U207 pin 8 (LBRIGHT).
11. The following waveforms should look like Figure 9-6 on the oscilloscope. The top two
traces are for the X Line Generator and the bottom two traces for the Y Line Generator.
X Line Generator
TP2
Y Line Generator
12.
Figure 9-7 illustrates the waveforms in step 11 expanded to show relative timing. the
second and fourth traces are delayed by 5 ms from the first and third. The oscilloscope
settings are changed as follows:
Sweep Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 ps/div
9-6 Controller Section
1 0 . 0 V/div 0 0 0 v
Figure 9-5. Switch Driver Waveform LCHAR
2 0 0 0 . 0 0 0 s