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Dynamic Focus 2 – Location
This second half of the dynamic focus circuitry stage consists of several
parts:
1. Horizontal ramp manufacture
2. Pulse manufacture
3. Current and voltage amplification
These circuit parts are similar to the first half of the dynamic focus cir-
cuitry except this stage:
· Creates a single width pulse instead of two different pulse widths
· Uses an N channel power MOSFET Driver Q7012 instead of a P chan-
nel device.
The purpose of the stages in the second half of the circuitry is to create a
pulse that locates the portion of the screen that needs dynamic focus
correction. Specifically, it is the area before and after the horizontal re-
trace pulse that corresponds to the right and left sides of the screen.
The voltage levels that come from the first half of the dynamic circuitry
determine the amount of correction. A higher supply voltage to driver Q7012/
D increases its dynamic focus signal level and consequently the amount
of outer focus correction.
Horizontal Ramp Manufacture
Capacitor C1615 at IC1502/pin 8 makes this ramp signal. Q1614 uses
horizontal pulses to reset the ramp. The resultant ramp is at the horizon-
tal frequency.
Pulse Manufacturing
There are two inputs in the pulse manufacturing stage. A horizontal ramp
waveform is input at IC1502/pin 4 (ch 2). A DC reference voltage is input
to pin 5 of this comparator. The reference voltage is chosen to produce a
low going pulse (ch 4) from the comparator prior to the next FBT retrace
pulse (ch 1).
121
P M 3 3 9 4 , F L U K E & P H I L I P S
c h 2 : p k p k = 3 . 3 6 V
ch1
c h 3 : p k p k = 6 . 1 1 V
T
ch2
1
ch3
2
ch4
3
C H 1 ! 2 . 0 0 V =
C H 2 ! 5 . 0 0 V =
4
C H 3 ! 5 . 0 0 V =
C H 4 ! 5 0 0 m V = A L T M T B 5 . 0 0 u s - 2 . 7 4 d v c h 1 +
W a v e fo r m D F f - P u ls e M fg .
N a m e
C h a n n e l 1
F B T p u ls e
C h a n n e l 2
H R e s e t p u ls e
C h a n n e l 3
R a m p v o lta g e
C h a n n e l 4
O u tp u t p u ls e
T im e b a s e
The low going pulse that outputs comparator IC1502 at pin 2 is reset at the
beginning of the next horizontal retrace pulse (Ch 2). To extend the output
pulse further, the comparator above it receives a horizontal retrace pulse
at IC1502/pin 6. The pulse is inverted and combined with the IC1502/pin 2
output. Finally, the composite output at IC1502/pins 1 or 2 is a low pulse
that starts before the retrace interval and ends at its conclusion.
Current and Voltage Amplification
The noisy 1.4Vp-p signal from IC1502/pin 2 is amplified by Q1505 and
buffered by Q1508 and Q1507 for sufficient current gain to drive Q7012.
Dynamic focus driver Q7012 receives the 12Vp-p gate signal and ampli-
fies it. The amount of its amplification is dependent upon its supplied
voltage. The DC supply voltage is higher for a wider picture. A wider
picture needs more dynamic focus correction at the sides.
D y n a m ic F o c u s O u t p u t S ig n a l
D C
f r o m T 7 0 0 1 / p in 1 1
N o r m a l 4 : 3 p ic t u r e
7 1 V
W id e 1 6 : 9 p ic t u r e
1 1 7 V
L o c a tio n
V o lta g e /d iv
F B T
N /A
Q 1 6 1 4 /b a s e
5 V p - p
Q 1 6 1 4 /c o lle c to r
7 V p - p
IC 1 5 0 2 /p in 2
1 .4 V p - p
5 u s e c /d iv
S u p p ly
V o lt a g e
Q 7 0 1 2 / D r a in
( O u t p u t S ig n a l)
1 7 8 V p - p
2 7 3 V p - p
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