Foundations Of 100 Hz Technology; Prerequisites For 100 Hz; 100 Hz Display Modes; Mode Aabb - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set

1.1 Foundations of 100 Hz technology

1.1.1 Prerequisites for 100 Hz

In order to double the picture frequency at the
receiver, the signals have to be read into the
relevant memory blocks and then read out
twice at double rate.
The following prerequisites must be met:
- The signals need to be digitised.
- The memory modules require at least 3
Mbits storage capacity.
- The software must be able to run a control-
ler, which in turn monitors the read-in and
read-out functioning of the memory.
- Suitable frequency-stabilized oscillators for
generating the clock frequency must be
provided.
- The drive signals for the output stages, line
and field deflection, and the E/W correction
must also be at double frequency.
- The power output stages for deflection, as
well as the deflector itself, need to be de-
signed for the higher frequency and the re-
sulting higher currents.
- The RGB output stages need to be able to
process the doubled bandwidth.
Document Q 2500
1.1.2

100 Hz display modes

When examining display modes the deflection
raster and the video raster need to be consid-
ered together. In 50 hz operation, the two sin-
gle-frame pictures A and B are written to the
scanning system 'a' and 'b', i.e. every second
line of frame A and the intermediate lines of B.
This is achieved in that the flyback of 'a' be-
gins in the middle of a line. Trace 'b' starts
also in the middle of a line but is written to the
end of a complete line. The next trace 'a'
starts again at the beginning of a line. The
trace time, however, is always the same.
1.1.3

Mode AABB

The simplest case of 100 hz operation in-
volves a simple doubling of single-frame pic-
ture display, i.e. field A is displayed twice con-
secutively followed by field B (AABB).
To achieve this the deflection raster must be
modified so that ‚a' is written twice followed by
'b' (aabb). Theoretically, this can be accom-
plished in two ways. Firstly, by adjusting the
flyback's starting time for the 4 single frames.
A half-line more is written for 'a1' and a half-
line less in for the third field. In practice, such
a scheme would be quite difficult to imple-
ment. In comparison, the second possibility is
easier to achieve. This involves shifting the 2
rd
and 3 fields (a2 and b1). This can be accom-
plished by adjusting the current though the
deflector by modifying the base resistance.
This produces the same time interval for all
traces over all fields
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