2.
In the monochrome mode, the output of FL1 splits two ways; one path is amplified and goes to
the sync separator; the second path is across R9. R9 sets the maximum output level of the luminance.
This level is then amplified, filtered, peaked, de-emphasized and smear-corrected before passing to the
YE-2 board. The Y signal luminance is not processed for chrome frequency inter-modulation and
distortion as is the color mode output of FL2. After color video levels are determined by FL2, this
output is buffered by Q3. The higher frequencies are preemphasized by a parallel RC network (C9 and
R16) and the luminance is again buffered by Q4. Then L2 and C11 (at the base of Q5), whose series
resonant frequency is slightly over 2 MHz, attenuate the higher and lower frequencies and give emphasis
to the midband of the luminance signal. The output of Q5 is then tuned by a passive equalizer
(transformer T1, L3, and C12). The center frequency of this tuner is determined by the adjustment of
T1. R23, at the output of this equalizer, sets the maximum output level of the color luminance. Q10
will ground whenever the broadcast address track is used. The video heads will see the time code track
as 200 KHz information. Q10 will receive a pulse if time code is present and will then take capacitor
C22 to ground. The time constant of C22 is such that only the 200 KHz information will be filtered.
3.
The primary purpose of the next section of IC-1 is to mute the luminance. There is a switch (on
the output of the color/luminance amplifier and the B&W/luminance amplifier) that will open whenever
a video mute condition exists. The filter at the input to peaking amplifier Q6 removes any residual
luminance carrier and provides series attenuation at 3.58 MHz. Q6, a common base amplifier, drives the
smear correction circuit, composed of Q7, Q25, and Q8. The luminance output of the DM-7 board now
passes to the YE-2 board, a noise eliminator.
Learning Event 5:
FUNDAMENTALS OF THE NOISE ELIMINATOR CIRCUIT AND Y/C MIXER (YE-2 BOARD)
1.
Refer to Figure 4-4 (fo) at end of lessons. The luminance video signal from the DM-7 board
enters the YE-2 board at connector 1 pin 2 and splits two ways. One goes through Q9, the dub
luminance buffer, which bypasses the noise eliminator. The output of Q9 goes directly to pin 1 of the
dub connector on the rear panel. This output contains the luminance signal plus a 6VDC level used to
control the dub luminance input switch in the recorder. The second path enters two delay lines, DL1 and
DL2. DL1 is a fixed delay of 300 nanoseconds and DL2 is adjustable in 100 nanosecond increments, up
to 300 nanoseconds maximum. This delay ensures that the luminance and chrome will arrive in phase at
the mixer.
2.
Q1 is a buffer with an output that feeds the base of Q2 and Q5. Low frequency noise passes
through the IC filter, C22 and K2, to the emitter of Q5. High frequency noises pass through the RC
filter, C7 and R10, and is amplified by Q3. Q4 then buffers the signal and diodes D1 and D2 clip the
positive and negative spikes. R33 sets the amount of high frequency noise seen at the emitter of Q5.
Here the processed high and low noise signals and the chroma signal are mixed with the luminance
signal on the base of Q5.
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