Memotech Limited MTX 500, Service Manual

Page: 46 / 78

42
Further information on the UM 1286 Modulator.
The Pal-Modulator is used to encode the R-Y, B-Y and Y
signals from the MTX home computer and to modulate them
together with the sound signal to a high frequency
(591.250 MHz).
R-Y and B-Y are called the Chrominance signals.
All the information about the brightness is in the Y
signal called the Luminance signal.
The Pal Encoder is built up around the LM 1889 and the
UM1286. The LM 1889 integrated circuit receives the R-
Y and B-Y signals from the video processor and provides
the colour signal to the Modulator. This one also
receives the Luminance signal (Y) from the video
processor and the audio signal from the 76489 (SE) and
provides a composite signal suitable for the antenna
input terminal of a TV receiver.
Fig i shows a functional block diagram of the system.
MTX Service Manual