Switch Off Flash Suppression; Rotation Panel; Raster Correction - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
range of the cut off control is not exceeded.
This means an optical comparison of the
raster 2 voltage is ruled out. A comparison
using a voltmeter is also very unreliable, as
the voltage source with approx. 500 MOhm is
very resistive.
A comparison of the raster 2 voltage is there-
fore made in service mode.

2.9.2 Switch off flash suppression

Transistors Q 3341 and 3343 are responsible
for suppressing fluorescent flashes on switch
off, caused by c.r.t. charges that are not dis-
charged quickly enough via the bleeder in the
DST. On start up and during operation they
have no function, as the base and emitter of Q
3341 are at the same level it is therefore
blocked, as is Q 3343.
Switch off flash suppression
D3391
D3381
D3371
Q3343

Raster correction

"Face to East" comparison
Document Q 2500
U12
D3342
C3341
D3341
R3344
C3342
R3343 Q3341
R3342
R3341
"Face to North"
On shut down the base of Q 3341 via R 3341
very quickly becomes zero volts. Due to Diode
D 3342, that is blocked in the direction of the
power supply, Elko C 3342 cannot discharge.
Q 3341 switches through and that in C 3342
can switch through via the emitter-collector
the output side connected transistor Q 3343.
In this way the RGB signals that control the
output stage IC's are directed to earth.
Fluorescent
avoided.
Until Elko C 3342 is discharged and the circuit
becomes ineffective, the c.r.t. discharges via
the bleeder.

2.10 Rotation panel

2.10.1 Raster correction
So as the earth's magnetic field affects the
colour uniformity of the c.r.t.s, it also influ-
ences the picture raster. For a geometrical
comparison, a definite alignment towards east
("face to east") is therefore prescribed.
If the device is turned towards another point of
the compass, rotation of the picture on the
screen occurs according to the type and size
of c.r.t. and local characteristics.
Raster rotation
40
image persistence
Correction of raster
rotation by rotation panel
© Loewe ProCollege
is thus