Tektronix Grass Valley 4000, Installation And Service

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Section 2 — Installation
Procedure for Checking Input Timing
For this procedure, you will need a Serial Digital to Analog Converter (DAC) with
known fixed delay and an oscilloscope triggered on the switcher analog reference.
The output of the converter should have sync on the green (or Y) output. Make a
note of the settings of the rotary switches on your switcher.
NOTE:
When measuring the timing, don’t forget to subtract the delay of the DAC used
in this test as some DACs have significant delay. Refer to the specifications for the DAC
you are using. (The GVP SMS8103 has a 6 µS minimum delay, for example.)
1. Connect the switcher analog reference to one channel of the oscilloscope and
the green or Y output of the DAC to the other channel.
2. Connect the serial digital input under test to the input of the DAC.
3. On the oscilloscope, verify that the serial digital input timing is within the
autotiming window corresponding to the Sync Generator rotary switch
settings. Use the timing diagrams (see
Figure 2-56 or Figure 2-57 ), to determine
the center of the autotiming window relative to the switcher analog reference.
For example, a Model 4000-3 switcher with a Sync Generator setting of 800
must have inputs arrive within -8 µS to +18 µS of the switcher reference.
Setting the rotary switches to 6ED centers the autotiming window around the
reference (0 offset).
4. Do this for each serial digital input to determine if you need to adjust the
rotary switches.
NOTE: If the switcher has analog video inputs in addition to serial digital inputs,
changing the setting of the Sync generator rotary switches will affect the timing of the
analog inputs.