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Performance Verification: Analog Section
WFM90D and WFM91D Service Manual
4-11
Vector Phase Stability
This procedure verifies the following requirement:
Phase Shift with Subcarrier Frequency Change from F
SC
to F
SC
ᐔ50 Hz
(F
SC
ᐔ10 Hz PAL): ᐔ2°. Phase Shift with Burst Amplitude Change from
Nominal to ᐔ6dB:ᐔ2°. Phase Shift with Variable Gain Control Varied from
+3 dB to --6 dB: ᐔ1°.
1. Connect a 75% color bar signal to the VIDEO IN connector. Set the input
switch to the 75 Ω position.
2. Select VECTOR display mode on the WFM90D or WFM91D monitor.
3. Use the Phase controls to position the burst vector on the 180° graticule line.
4. Check that when the television generator subcarrier frequency is changed
ᐔ50 Hz (ᐔ10 Hz PAL) from nominal, that the display locks, and that the
burst phase has changed ᐔ2° or less.
5. Return the subcarrier frequency to nominal on the television signal generator.
6. Replace the color bar signal on the VIDEO IN connector with a black burst
signal.
7. Check that the vector phase changes less than ᐔ2° while varying the burst
amplitude from nominal to ᐔ6 dB (1/2 to 2X amplitude), using the
television signal generator burst amplitude control.
8. Return the burst amplitude to nominal on the television signal generator.
9. Select VAR GAIN ON from the Configuration menu.
10. Check that the vector phase changes less than ᐔ1° while varying the vector
burst amplitude from 1/2 to 1.5 times nominal amplitude using the variable
gain control.
11. Select VAR GAIN OFF from the Configuration menu.
12. Remove the signal input from the VIDEO IN connector.