Important Voltage Waveforms In The Dtb Control Logic - Philips PM32671 Service Manual

2-26
i s applied via the Darlington pair V219, V209, the voltage divider R239, R238 and emitter-follower V221
t o the input of the Schmitt trigger D203 (1,2,3), which i s the end-of-sweep detector.
I f this voltage has reached a value o f +I
Output D203-3 now becomes L and is inverted t o give H on output D203-8, which i s applied to pin 6 of SR
flip-flop D204 (1
Output D204-13 becomes L and also the reset input D207-1 and the DTB stops as switching transistor
V228 conducts again. I n this way, the charging of the timing capacitance stops, and these are discharged
via V227 a t the start of the hold-off period.
The situation described above i s valid if the DTB sweep is completed before the MTB sweep (see Fig. 2.8.
indicating the voltage waveforms for the DTB SWEEP COMPLETED mode, and also for the DTB SWEEP
NOT COMPLETED mode).
I n the DTB SWEEP NOT COMPLETED mode, the state of the
stopped i f input D203-5 becomes L a t the end of the MTB sweep. Now input D204-12 becomes H and
flip-flop reset input D207-1 becomes L.
DTB SWEEP COMPLETED
Fig. Important voltage-waveforms in the DTB control logic
2.3.5. Final X Amplifier (see Fig. 8.1 3)
The input stage comprises a balanced series-feedback amplifier, V1371, V1372 with common current source
MTB or DTB sawtooth or the X DEFL. signal. The base of V1372 receives an adjustable d.c. voltage derived
from the X POSITION control R5.
This control, R5, consists of two ganged sections, one of which has a degree of backlash t o enable fine and
coarse adjustment of the X position with one knob.
The amplification of the V1371, V1372 stage in increased by x10 if the X MAGN control is pulled. Relay K1371
is energised in this mode and additional emitter resistance (R1378 and R1381) is switched into circuit.
The collector of transistor V1371 drives one half of t h e final X amplifier, the other half being driven by the
collector of V1372. The configuration of both amplifier halves i s the same, but corresponding transistors are
complementary (PNP vs NPN) so corresponding supply voltages are therefore reversed (V1316 vs V1312).
One half o f the final X amplifier consists o f V1302 (NPN to adapt d.c. level). V1306 (PNP shunt-feedback
amplifier), V1311 (PNP, t o adapt d.c. level), V1312 (NPN, current source) and V1313 (NPN, output emitter.
follower).
The signal conditions are as follows:
I f the sawtooth voltage on the base o f V1371 rises, the collector current falls. The voltage level on the junction
base becomes more negative, so the collector potential of V1306 rises. Also the potential on the junction of
collectors V1311, V1312 rises and is applied via emitter-follower V1313 t o one horizontal deflection plate.
During the flyback of the sawtooth, diode V1308 can conduct. The feedback components of V1306 are
...
6). The flip-flop switches over and gives
DTB SWEEP NOT COMPLETED
DTB
SWEEP
H on input D204-11.
a logic
RS flip-flop is not changed and the DTB is
MAT 915A
via transistor