Horizontal Deflection; Horizontal Driver; Horizontal Output - Zenith Z-100 PC series Service Manual

Horizontal Deflection
The horizontal deflection circuitry is responsible for
generating the scanning current needed in the
horizontal deflection coils to fill the width of the
raster. Three main stages are involved here: the
horizontal driver, horizontal output, and pincushion
(PIN) correction circuits. Because the ZCM-1490
employs a flat technology CRT, the PIN circuijry is
more elaborate than in previous monitors. The PIN
circuitry is described in a separate section.
Horizontal Driver
Transistor 03403 is the horizontal deflection driver.
This driver acts as a buffer or isolation stage to pre­
vent 'the horizontal output circuit from changing the
oscillator frequency. The horizontal oscillator output
voltage is applied to the base of 03403. The output
of this stage, taken at the collector, is applied to the
interstage transformer (TX3401). R3428 and C3409
dampen the primary of TX3401. The transformer
steps down the B+ voltage supplied through R3429
to match the low-impedance drive of 03003. C3009,
R3007, and R3009 shape the resulting base drive
waveform for 03003.
Horizontal Output
Transistor 03003 is the horizontal output transistor.
Refer to the following parts of Figure 5-3 while read­
ing this circuit description. Figure 5-3a shows the out ­
put voltage waveform at R3009. The corresponding
amplifier current in Figure 5-3b shows that 03003 is
cut off during retrace plus a part of the trace at the
left side of the raster. Diode CR3003 conducts during
this time, producing part of the trace at the left side of
the raster and reducing the average amplifier current
(thus increasing efficiency). Figure 5-3c illustrates
this damper current. Combining Figures 5-3b and 5­
3c yields the sawtooth current needed for a complete
trace from left to right, as shown in Figure 5-3d.
®
DRIVER TRANSFORMER
OUTPUT VOLTAGE
~
@
AMPLIFIER CURRENT
©
DAMPER CURRENT
@
SAWTOOTH SCANNING
CURRENT
Figure 5-3. Horizontal Output Amplifier
Waveforms
03003 and CR3003 are the essential parts required
for horizontal deflection. 03003 is the horizontal
power amplifier while CR3003 is a damper diode
used to increase efficiency. Immediately afterflyback,
CR3003 is forward-biased by the negative voltage
stored in retrace capacitor C3008. CR3003 rectifies
the stored energy of the yoke and the core of T3001,
thereby recharging capacijors C3006 and C3007.
Damping is needed because the oscillations produce
whije vertical bars at the left side of the raster.
In summary, the resulting current waveshape is re ­
lated to horizontal scanning as follows:
1. Damped current produces the left side of a
trace.
2. As the damped current diminishes and the out ­
put stage begins to conduct, the beam is at the
center.
3. Current from the output amplifier produces the
remainder of the trace.
Series linearity coil LX3002 provides a varying in ­
ductance with changing yoke current, resulting in im ­
proved linearity. R3003 and C3004 prevent ringing in
the coil which might occur with fast changes in signal.
Circuit DeSCriptions
Page 5-7