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Troubleshooting Procedures
6–40
WFM 90 and WFM 91 Service Manual
Use this procedure when
the graticule is ok, but the
Audio display is distorted
or not visible.
Remove the Display module and the
Backlight board. Power up the instrument
and select DEFAULT PRESETs from the
CONFIGURE menu. Select the Audio
display mode. Attach an audio input signal
from 0 to +8 dbu.
No
Yes
No
Yes
Replace the
Top board.
Check the AUDIO IN signal:
(J15 is on the Bottom board.)
J15-4 = Check for a gain of X1 above
input signal level. The Audio Amplifier
gain is always X1 in +8 dbu. The signal
level should change as different
reference dbu levels are selected from
the menu.
Is the
AUDIO IN
signal ok?
Check the audio deflection signals:
(J9 is on the back of Top board.)
J9-1 = 1 Vpp, 2 VDC
J9-3 = +1 V to +3.8 V ramp with a
35 ms period
Are the audio
deflection signals
ok?
Replace the Input board.
Replace the Bottom board.
Figure 6–20: Flowchart for bad audio display