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(7) Give the UUT a warm-up time of 5 minutes.
(8) Video Input Adjustment
(a) Set the video pattern generator for a white-raster output.
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(b) Connect the VC4 cable from the oscilloscope to the BNC tee
adapter T1.
(c) Get a video signal waveform as shown in Figure 112.
(d) Adjust the video signal output of the video pattern generator
accurately to 1.0 Vp-p in amplitude as measured on the
oscilloscope.
(9) Connect the VC4 cable to the BNC tee adapter T2 to measure the video
output of the VMU tuner.
(10) Set the VMU tuner for reception of CHn and make sure that the
oscilloscope shows a video signal waveform as shown in Figure 112 or
Figure 140.
(11) Find the variable resistor A2VR201 for adjustment of the CHn
modulation depth. Refer to Figure 138 for the location of the CHn
A2 card and Figure 139 for the location of the variable resistor
A2VR201 on the A2 card.
(12) Turn A2VR201 fully counter-clockwise to make the modulation depth
0%.
(13) Slowly turn A2VR201 clockwise until you get the video signal
waveform as shown in Figure 140.
NOTE: Do not turn the variable resistor counter-clockwise to adjust
the modulation depth. Always turn it clockwise to adjust.
This is to prevent the output saturation.
0.7 Vp-p
0.26 - 0.3 Vp-p
MODULATION DEPTH ADJUSTMENT
Figure 140
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(14) You can adjust the modulation depth of other channels as continued
from the above.
(15) When you complete the modulation depth adjustments, click on the
"USER CONFIG" button to put the user configuration back into the
UUT.
(16) When the user configuration is shown, click on the "END" button.
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D. Output Level of Internal Video Signal Generator
(1) Use the same setup as the functional test setup (Figure 111).
(2) RF Output Connections
(a) Connect the input of the VMU tuner to the tester's RF OUTPUT RF1
connector with two RF cables (RFC2 and RFC3) and a 20-dB RF
attenuator.
(b) Connect BNC 50-W terminators to the RF OUTPUT RF2, RF3 and RF4
connectors of the tester.
(3) Start the adjustment mode (ref. 5.B.).
(4) The user configuration is initially shown. Change the CH2 settings
as follows:
(a) If the frequency is not 163, change it to 163.
(b) Click on the "OK" button.
(5) Click on the "BITE OFF" or the arrow mark on its right side. You
will see a pull-down menu as shown in Figure 137.
(6) Click on the "BITE ON" of the pull-down menu. You will hear a
"click" (from the UUT's A8RL501).
(7) Give the UUT a warm-up time of 5 minutes.
(8) Connect the VC4 cable to the BNC tee adapter T2 to measure the video
output of the VMU tuner.
(9) There are two types of the A8 card: first or second. The first type
has two variable resistors and the second type has one variable
resistor. Go to:
· Step (10) if the UUT has the first type A8 card
· Step (11) if the UUT has the second type A8 card.
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(10) First Type A8 Card
Refer to Figure 141 for the location of the variable resistors
A8VR501 and A8VR502.
VR501 VR502
A8 CARD CN503
BOTTOM
TOP
FRONT REAR
LOCATION OF VARIABLE RESISTORS ON A8 CARD
Figure 141
Do the output level adjustment as follows:
(a) Set the VMU tuner for reception of CH2 and make sure that the
oscilloscope shows a video signal waveform as shown in Figure
142.
(b) Turn A8VR502 and adjust the amplitude A of the video signal
shown on the oscilloscope to 0.8 Vp-p.
A8VR501 ADJUSTS
THIS LEVEL.
A8VR502 ADJUSTS
THIS AMPLITUDE.
BL = 0.3 Vp-p
A = 0.8 Vp-p
ADJUSTMENT OF OUTPUT LEVEL OF INTERNAL VIDEO SIGNAL GENERATOR
Figure 142
(c) Turn A8VR501 and adjust the level BL of the video signal to 0.3
Vp-p.
(d) When you complete the output level adjustment, click on the
"USER CONFIG" button to put the user configuration back into the
UUT.
(e) When the user configuration is shown, click on the "END" button.
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COMPONENT MAINTENANCE MANUAL Video Modulator Unit (VMU)(80)
