Switching Of The Speed Modulator - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
W3201
to signal board
CUTOFF
Q3181
C3182
R3181
R3185
Q3171
C3172
R3171
R3175
Q3161
C3162
R3161
R3165
C3204

2.8.2 Switching of the speed modulator

The circuit is located on the c.r.t. PCB and is
supplied with RGB signals from TDA 9332 via
pins 40/41/42.
The RGB signals are applied to connector
W 3201 pins 4, 6, 8 at 3 Vss and are then fed
via impedance converters Q 3181, Q 3171
and Q 3161. To detect changes in all three
colours, the signals are decoupled by capaci-
tors C 3201, C 3202 and C 3203 together.
The resulting signal is differentiated with
C 3204, R 3204. Control via the RGB signals
offers the advantage that this circuit also
works with Teletext and OSD operation.
This means that when steep signal changes
occur there are only oscillation packages with
max. 0.3 Vss on the emitter of transistor
Q 3204 for processing.
Document Q 2500
U12
Q2500 Speed modulator
U12
R
U12
C3208
G
R3207
R3208 R3209
U12
Q3204
R3206
B
Q3211
R3211
R3212
R3156
C3158
Q3157
R3215
Q3216 D3218
R3220
R3217
R3216
C3216
The input for the circuit of transistor Q 3204
has a low resistance input, so that it can proc-
ess steep slopes. From the collector the 4 Vss
signals are led to the impedance converter Q
3211. This supplies the signal at 6 Vss to the
push-pull output stage Q 3221 and Q 3222.
The two transistors are current counter cou-
pled and amplify the signal to a maximum 50
Vss. All voltage data refers to a black/white
change and maximum contrast.
Via the voltage dividers R 3221, R 3222, R
3223 and R 3224 one end of the correction
coil on pin 1 of W 3258 is set to 30 V.
The two transistors Q 3221 and Q 3222 are
blocked without control, so that the other end
of the coil is hanging free and no current flows
through the coil. Deflection occurs only via the
horizontal deflection coil.
For a positive pulse transistor Q 3221 is
blocked and Q 3222 conducts. This causes a
current to flow via R 3221 and R 3222 through
the booster coil and via Q 3222 to earth,
which accelerates the deflection.
If, however, a negative pulse is felt, then Q
3221 conducts and Q 3222 is blocked. The
36
to W548 basic board
W3301
5pol. ws L3366
4u7
R3366
270R
Uvid
C3156
R3229
C3221 C3154
Q3221 C3157
C3222
N60
R3222
R3227
C3219 L3226
W3258
Q3222
C3223
R3228
© Loewe ProCollege
C3366
22u
R3226
470R 470R
SVM
to booster coil