Philips PM3208 - 4.2 Horizontal Deflection

4.1.6
4 CIRCUIT DESCRIPTION
Vertical output amplifier
The output from the intermediate amplifier is fed to the vertical output amplifier. In this
circuit, the vertical signal is amplified to a sufficient amplitude to drive the vertical
deflection (Y) plates, of the CRT.
4.2 HORIZONTAL DEFLECTION
4.2.1
4.2.2
Trigger amplifier
From the first stage in the vertical amplifier, Q5-Q6, the vertical signal is fed to the
trigger amplifier, consisting of Q9-Q10. (Q105-Q106 and Q111-Q112 for Ch. B). The
mode-selector in the vertical switching circuit defines whether Ch. A or Ch. B is fed to
the trigger generator. Control takes place via the diodes D75-76-175-176 by means of the
flip-flop |C202 pins 5 and 6.
Trigger generator
Input signals to the trigger generator are:
- internal trigger signal Ch. A or Ch. B from the trigger amplifier
- line trigger signal from the line-transformer via R1025
- external trigger signal from the external trigger input
Selecting these signals can be performed with the trigger source switch, $401.
Trigger-mode can be selected by means of the coupling switch, $402.
- In position "AC", only a.c. signals perform triggering. (from 10 Hz)
- In position "AC-LF", a.c. signals between 10 and 15000 Hz perform triggering.
- In position "TV", triggering on TV-frame pulses is possible.
- In position "DC", there are no restrictions. This means that all kinds of signal will act
as trigger pulses.
The trigger level is adjusted with the level-potmeter RV441a, by means of Q404-Q405.
Triggering on the positive or negative-going edge of the signal is defined by the slope
switch, part of RV441, which determines whether the trigger signal is taken from Q404 or
Q405. The trigger pulse is amplified and via a gating circuit 1C401 fed to the sweep
generator. In the trigger generator, also provisions have been made for horizontal (X)
deflection. In this case, the horizontal deflection is not controlled by the time-base
generator, but by other signals. The kind of horizontal signal can be selected by means
of the trigger source switch. In this case, the output from Q403 via CN404 is used to
drive the horizontal deflection. Hold-off control potmeter RV441b is part of the sweep
generator and will be described in that section.
4.2 HORIZONTAL DEFLECTION