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The CRT for the 1493, 1793 and 2093 monitors have a 90° deflection angle. The
1993 incorporates 100° while the 2793 CRT has 110° and the 3693 has 111°
deflection angles. These picture tubes have integral implosion protection and a
EHT of 25KV.
Blanking is accomplished by setting the gain of the interface IC to zero during
blank time. The Horizontal Blanking pulse is generated by amplifying the flyback
pulse. The Vertical Blanking pulse is started by the vertical oscillator one shot
and ended by the counter in the auto bias IC via the "bias out" pulse. The Master
Gain control, located on the remote PCB, sets the gain of the video signal when
blanking is not active. The Beam Current Limiter circuit, which is designed to
keep the FBT from overloading, will reduce the video gain if the maximum
average beam current is exceeded. Also, the beam current is reduced if the FBT
approaches maximum operating temperature.
The
Sync Interface can accept separate or composite sync. Two comparators are
used to receive sync, one for vertical sync and the other for horizontal sync.
Resistor dividers are used to protect the comparator IC from over voltage damage.
For customers who do not require interlace, an additional vertical sync
stabilization circuit is included. This circuit synchronizes the vertical sync to the
horizontal cycle.
1. One shot.
2. Ramp generator.
3. Vertical drive.
4. Vertical output.
The Vertical Control & Output circuit consists of:
The
Vertical Oscillator generates the vertical free running frequency when no
vertical sync is present. When sync is applied, the vertical oscillator synchronizes
to the leading edge of the sync pulse.
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The Vertical Dynamic Focus amplifies the parabolic waveform across the
vertical coupling capacitor from about 3Vp-p to about 200Vp-p, depending on CRT
requirements. This waveform sharpens the top and bottom portion of the raster
on dual focus CRT's.
The
Horizontal Dynamic Focus amplifies the parabolic waveform across the
horizontal coupling capacitor, using a transformer to produce 300Vp-p output from
an input that is about 33Vp-p. This waveform is added to the vertical dynamic
waveform and sharpens the right and left sides of the raster.
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