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TECHNICAL DESCRIPTION
below its half amplitude point, producing a stable sync called PRECN-
SYNC.
6.5.4
Colour Frame Detector (6150-31)
Monostable U1a is triggered by the leading edge of PRECN-SYNC and
times out about 6 µsec later. U1b is triggered by the trailing edge of U1a,
generating a burst sample window CBWINDOW (available at test point
CBW) at the mid point of the burst. The length of CBWINDOW is slightly
less than one half cycle of subcarrier (approx. 70 nsec) for colour frame
operation, and slightly more than one subcarrier cycle (approx. 250 nsec)
for non colour frame operation. CBWINDOW is used to drive a burst phase
discriminator in the LCA.
Burst, (CB) extracted from the video by U4e and U4f is fed into the LCA.
phase discriminator U1b.
during the WINDOW at the appropriate line, in the first field of a frame, then
U9b is clocked on, generating a colour frame pulse (CFP) input to the
MCU.
Calibration of the colour frame detector is accomplished by adjusting CFP
ADJ VR1 for NTSC or VR2 for PAL.
connected to an RS-170-A (8 field PAL) video source and properly
terminated. The unit must also be set up to operate in the colour frame
mode.
You will need a sync pulse generator with a colour field #1 identification
pulse output, and a dual channel oscilloscope to perform the calibration.
1.
Display the colour field #1 ID pulse from your sync generator on
channel A of your oscilloscope. Set up the time base to show
two pulses.
2.
Connect channel B of your scope to CFP test point.
3.
Position VR1 near the centre of its range so that a pulse
appears on channel B two frames before the second pulse of
channel A. Continue adjusting VR1 clockwise until the pulse
disappears. Mark the position of VR1 with a pencil. Adjust VR1
counter clockwise until the pulse reappears and disappears
again. Mark the position of VR1 with a pencil.
4.
Position VR1 halfway between the pencil marks. The LOCK
LED should be on.
6.5.5
Telecine Interface Logic (6150-32 & 6150-33)
Bi-phase quadrature tach pulses from the telecine are fed from the 9-pin D
Parallel I/O connector to quatrature decoder U14. These TTL level pulses
usually come at a rate of 10 pulses per film frame. The 4025TR can also
accommodate tach rates of 1 or 2 pulses per frame. For best results use
Model 4025TR Film Footage Encoder Manual
If a positive going transition of burst occurs
The generator input must be
Page 6-15
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