Table of Contents
Advertisement
3DQDVRQLF
11. COLOUR OUTPUT STAGE
The Y-Board, contains not only the colour output
stage, but also scan velocity modulation (except
model TX-21MD4 which has no SVM stage).
The RGB signals fed to the colour output stage are
fed from the VDP
IC601
38 (G out), 39 (B out), where these signals are fed
via the common base configured transistors Q301,
Q303
and Q305, which provided good high
frequency response, these signals are then buffered
and amplified by transistors Q302, Q304,
before finally being fed via connectors E8 and Y2 of
the Y-Board. The RGB signals at this point being
approximately 5Vpp.
The velocity modulated (VM) signal which is a
combined RGB signal, is output from the VDP
via pin 34 is also fed via a common base configured
transistor in the form of Q950, and from here via
Q951
where the signal again is amplified and
buffered before being fed to the Y-Board via
connectors E8, Y2 pin 7.
11.1. Velocity Modulation circuit
The SVM signal which is fed via connector Y2 is
then fed to the base of transistor
capacitor C906 and R914 shape the signal.
The signal is then fed from here to two mirror image
push pull output stages which are used to supply the
required current to the velocity modulation coils.
Transistors
Q906
and
impedance converters which control the output
stage at low impedance without distortion.
pins 37 (R out),
Q306
IC601
Q905
where with
Q907
are connected as
Transistors
Q908
at approximately 35Vpp, via connector Y6 pins 1
and 3 to the SVM coils, the scan coils being
controlled directly from the collector terminals of
transistors
Q908
and
is coupled in parallel to the deflection winding.
11.2. CRT AMPLIFIER STAGE
11.2.1.Outline
In order to avoid damage caused by long cathode
lines and there by trim the frequency response, the
RGB output stage is mounted onto the CRT board.
Each of the 3 colour channels are fed to
(TDA6103Q) which has a bandwidth of 7.5MHz
guaranteeing good resolution even with rapid signal
transitions in both directions.
The use of
IC351
components in the colour output stage are reduced
to a minimum, the colour output stage being driven
directly by the VDP IC601.
The RGB signals input to
approximately 90Vpp before being output from
IC351
via their respective outputs with Red output
via pin 9, Green output via pin 8 and Blue output via
pin 7.
A reference voltage for the internal amplifiers is also
fed to
IC351
pin 5, while negative feedback to
determine the amplification factor is provided by the
resistance between the input and output pins of the
RGB signals, this resistance being provided by
resistors R357, R358 and R359.
22
and
Q909
then outputs the signal
Q909
via resistor R929 which
means that the number of
IC351
are amplified to
IC351
Advertisement
Chapters
Table of Contents
