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Troubleshooting Procedures
6–38
WFM 90 and WFM 91 Service Manual
Use this procedure when
the graticule is ok, but the
Waveform display is
distorted or not visible.
Remove the Display module and Backlight
board. Power up the instrument and select
DEFAULT PRESETs from the CONFIGURE
menu. Select the Waveform display mode.
Is the
VIDEO IN
signal OK?
Check the Waveform display
mode horizontal and vertical
deflection signals:
(J9 is on the back of the Top
board.)
J9-1 = 1.3 Vpp, 2 VDC (vert.)
J9-3 = 2.2 Vpp, 2.3 VDC (horiz.)
Are the
deflection
signals
ok?
Replace the Input board.
Replace the Bottom board.
Replace the Bottom board.
Is the
VIDEO
IN signal
ok?
Check the input DC clamp circuit:
Short J14-4 to the GND pin on the
Bottom board with a jumper wire.
Check the VIDEO IN signal:
J14-2 = 1.3 Vpp, 0.3 VDC
blanking level.
No
Yes
No
Yes
No
Yes
Check the VIDEO IN signal:
J14-2 = 1.3 Vpp, 0 VDC
blanking level.
Check the horizontal and vertical size control
voltages:
(These voltages are set in the CALIBRATION
MENU.)
J9-7 = 0.9 VDC
J9-8 = 1.2 VDC
Are the size
voltages ok?
Replace the Bottom board.
Replace the Top board.
No
Yes
Figure 6–18: Flowchart for distorted waveform display