~-------
~
945424-9701
. +s voe
1N914B
R17
FROM
COMPOSITE
SYNC
DIFFERENCE
AMPLIFIER
'(A)136277
R23
FROM
AUX
H-SYNC
GE
Figure 1-27. Model 911 VDT Power/Logic
PWB
Vertical Sync
Generator Schematic Diagram
-t5VDC.--,.....~
R36
R24
CB
14
15
-t5
voe
R30
R31
H-SYNC
Q
1-4-------+--i
PULSE
U4
FROM
DIFFERENCE
AMPLIFIER
COMPOSITE
I
SYNC
CRTC
K
CR17
STRETCHER
_!.._
Cl!
1'
(B)136278A
CIS
U6
TERMINAL
READY
RE-
Ii
TRIGGERABLE
12
NOT
~---c_R_s
__
_._!
o_,
MONOSTABLE
USED
CRTCLK
U6-4
HOR.
SYNC
~
r-
25
µSEC
Ull
CRl6
SYNC
LED
+S
VLS
Figure 1-28. Model 911 VDT Power/Logic
PWB
Auxiliary ff-Sync
Generator Schematic Diagram
1N914B
VERT.
SYNC
'Y"~...._.
TO
CRT
MONITOR
TO
DUAL-
GAIN
'--.AJ\,jl\r------
VIDEO
AMP
-t5
voe
R40
HOR.
J3-6
SYNC
TO
CRT
MONITOR
TERMINAL
READY
J2-5
TRDIT
2
TRD2T
J2-6
TO
VDT
CONTROLLER
The H-SYNC pulse
stretcher
monostable multivibrator (U2) in
the
H-drive generator changes
the
duty
cycle
of
the composite sync pulse
to
approximately 39% (25 microseconds low;
40
microseconds high). The stretched composite sync signal resets the
timer
and keeps
the
timer
reset for the duration
of
the low-level (25 microseconds) pulse. Since
the
frequency
of
the
composite sync signal (15. 720 KHz) is greater
than
the
"natural"
frequency
of
the
astable
multivibrator (approximately
15
KHz),
the
timer
"locks
in"
on
the horizontal
component
of
the
composite sync signal. The
"natural"
frequency
of
the
horizontal timer circuit is set
by
R30.
1-43
Digital Systems Division
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