Tektronix Grass Valley 4000, Installation And Service

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System Startup
Analog Input Timing
Analog Primary Sources
—Optional analog and chroma key external inputs are not
autotimed. Therefore it is necessary to time them to the switcher analog reference.
The timing diagrams show that the required arrival time of these inputs is
dependent upon the setting of the Sync Generator rotary switches. For a setting of
6ED, the analog input s must arrive in time (0 offset) with the switcher reference.
For a setting of 800, the inputs must arrive 5 µS after the reference. Analog inputs
can be timed using the oscilloscope method of comparison with the switcher
reference.
Chroma Key Input Sources
—Analog chroma key inputs are not visible on the
output of the switcher as primary sources, therefore, initial timing should be
checked using an oscilloscope. For proper chroma keys to be achieved, the external
chroma key inputs must arrive at the switcher in time with the analog reference.
The chroma key input is clamped using a local clamp pulse generated on the Sync
Generator which is derived from the switcher analog reference, not the external
input. Incorrect clamping time results in poor or unusable chroma keys.
Final timing compensation can be performed with a fine adjustment setting in the
main menu system under Config/Inputs/Chr key inputs. Although this timing
adjustment in the menu has a large timing range (more than 20 µS) it is intended
for artistic use and will not correctly compensate for a mistimed input.
In this Chroma Key menu, the value of the timing number should be in the vicinity
of +80. If it is more tan a few clocks from that, recheck the input timing of the
source.
With the Sync Generator switches set to 800, the external chroma key inputs
should arrive at +5 µS relative to the switcher reference. For a setting of 6ED on the
Sync Generator, the external chroma key inputs should arrive in time (0 offset)
with the swticher reference.