Loewe Q2500B Serviceanleitung Seite 166

Technology of Q 2500 colour TV set
On start-up C 479/22 µF is very quickly
charged up by R 471/22 k. For C 489/22 µF
charging occurs more slowly via R 477/10 k
and R 4476/33 k.
charging phase pin 9 is more positive with
respect to pin 10. On shut down C 489 dis-
charges rapidly via D 474 (which releases R
476) and R 477. Pin 9 is again more positive
with respect to pin 10 and mute is imple-
mented again internally.
TDA 7296 can be considered to be an opera-
tional amplifier. It is controlled by its non-
inverting input pin 3. The amplification is cal-
culated from the negative feedback combina-
tion R 478/473.
This results in
R 478
V = 1 + --------- = 1 +
R 473
The amplified signal is felt on pin 14 and for
the left channel is fed to the loudspeakers via
L 479.
The R 479/C 471 combination is necessary for
an internal bootstrap. In addition, the output
phase is equipped with an overload and tem-
perature protection circuit.
The two output stages are supplied with volt-
age symmetrically. It is taken from the trans-
former at zero potential and rectified and
smoothed by D 686/687 and C 687. With the
help of the R/C combination 466 and 468 it is
split into +/- 18 V (see also power supply).
This measure achieves a halving of the peak
current by the rectifier diodes D 686/687 and a
higher undistorted output performance, espe-
cially for low frequencies.
An output stage without any electrolytic ca-
pacitors contributes to this.
Document Q 2500
This means that in the
22 k
-------- = 33
0.68 k
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