Circuit - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
To compensate for this a rotation panel (raster
correction) is incorporated into the 81 cm de-
vice with chassis Q 2500. As the effect on the
raster is less on smaller and 4:3 tubes the
rotation panel is not required.
For the raster correction a circular coil is at-
tached to the cone of the c.r.t. If a uniform
current flows through it, the electron beam
rotates around its own axis. As the created
magnetic field overlays the field of the deflec-
tion coils, the picture can be rotated about its
central point.
R16
R21
W01
R23
1
2
U12
3
ROT
R11
In this way the inverting input of the opera-
tional amplifier on pin 9 of I1C is controlled on
the rotation panel. At maximum anticlockwise
rotation approximately 3.2 V is applied and at
maximum clockwise rotation 3.3 V. The opera-
tional point is adjusted on pin 10 by R21 and
R23. According to the voltage difference be-
tween pin 10 and pin 9 the push-pull stage
Q26 and Q28 is controlled. On the base con-
nections there is a voltage of 0.6 to 10.6 V.
The output voltage of the push-pull stage is
applied to pin 2 of the correction coil and at
the same time is fed to the inverting input of
operational amplifier I1A via R 38 and R41.
This also controls the second push-pull stage
Q 48/Q 47. The two OPVs and push-pull
stages counteract each other. This means that
a current can flow to earth via Q 26, through
the correction coil (from pin 2 to pin 1 on W31)
and via Q48. On pin 8 of the OPV there is a
voltage of 10.6V at maximum clockwise rota-
tion and on the other output pin 1, 0.6 V. Oth-
Document Q 2500
C17
C16
I 01C
10
+
8
C30
9
-
C23
C01
R12
R36
C11

2.10.2 Circuit

For raster correction the DAC on pin 25 of the
video/deflection processor TDA 9332 is used.
The voltage produced can be adjusted by the
user via "rotate picture" and in service mode.
It flows via W 1021, pin 3 to the rotation panel
W 1, pin 3.
Q26
C27 C47
Q28
2 1
W31
R42
R41
R38
R39
erwise the current flows via Q 47 through the
correction coil (in this case from pin 1 to pin 2
on W 31) and via Q28 to earth.
In this way the current can be adapted to the
required correction with respect to direction
and size. This correction can, however, also
act in reverse, if the coil is rotated on the de-
flector.
The control electronics for the rotation coil is
fixed firmly to the Q 2500 chassis. However,
the rotation coil and control electronics should
be considered as a unit. In the event of a fault
the coil is then changed as a complete unit.
41
Q47
I 01A
3
+
1
Q48
2
-
C02
© Loewe ProCollege
4
I 01
C12
11
C31