Philips PM32671 Service Manual page 37

The NOT TRIG'D indicator normally glows when awaiting
i) HORIZONTAL CHANNEL SELECTION LOGIC& HORIZONTAL CHANNEL SWITCH
MTB only (S2D depressed or all horizontal display mode switches S2 released)
In this mode, S2D feeds a logic L to the
output pin 9 is H and inverting output pin 8 is L. This L level causes transistor V208 to conduct and thus
opens signal path for the MTB sweep via transistor V224 and the diode V217 to the input of the final X
a
DTB only (S2B depressed)
In this mode, an L level is applied to the reset input pin 13 of D207. The
pin 8 i s H. The L output on pin 9causes transistor V223 t o conduct and thus opens the signal path for the
DTB sweep via diodes V211 and V214 to the final X amplifier.
EXT X-DEFL only (S2A depressed)
In this mode, both the input (10) and the
set
V295 and S2A-6 of the horizontal display mode switch. Consequently, outputs (pins 9 and 8) of flip-flop
D207 are H and both the MTB and DTB sawtooths are prevented from reaching the input of the final X
amplifier.
The external X deflection signal i s now routed via transistors V203 and V204, in the X DEFLECTION
AMPLIFIER, and switching diode V216 to the X FINAL AMPLIFIER.
ALT TB mode (S2C depressed)
Flip-flop D207 functions as a
level H, and the data input (12) is connected to the inverting output (8). The signal applied to clock input (1 1)
is the END OF SWEEP pulse. This signal goes L a t the end of the MTB sweep and goes
reaches the 0 V level. When the clock-pulse input goes from L to H the condition of the flip-flop changes.
For instance, output 9 goes H and the inverting output 8 goes L, so the MTB sawtooth is applied to the final
X amplifier. After the L to H transition, on the clock input, output 9 is L and inverting output 8 is H, which
applies the DTB sawtooth to the final X amplifier. A t the next transition, the MTB is again applied, and so on.
This stage is formed by integrated circuit D202, of which the transistors connected to pins 1, 15, 16 and 8,9,
current from R1238 and R1244 in the FINAL VERTICAL AMPLIFIER. These currents provide the trace
shift in the ALT TB mode.
The transistor connected to pins 2 and 1, and the transistor connected to pins 7 and 8 are current sources.
If the ALT TB mode is not selected, the currents from both sources are equal because the switch contact S2C
between pins 2 and 7 is closed. The output pin 1 of NOR gate D208 is
current from R1238 i s routed to D202-14 and then via an internal transistor to the current source on pins 2, 1.
is
When ALT TB mode selected, the contact between pins 2 and 7 of D202 i s open. Consequently, the current
of both current sources is no longer equal. Current source pin 2, 1 carries a lower current than current source
pin 7,8. The difference depends on the setting of the TRACE SEPARATION potentiometer R15. With R15 a t
zero resistance both currents are identical. If the DTB is displayed, NOR
routing of the currents of R 1244 and R 1238 over both current sources are identical to the situation without
ALT TB selected. Only the magnitude of the currents differs, that from R1238 being higher than that from
currents in R1238 and R1244 are equal.
In the MTB sweep that follows, the MTB is displayed and the output D208-1 is now H. As a result, the
currents from R1238 and R1244 in the FINAL VERTICAL AMPLIFIER are routed via another path in D202.
The current from R1244 is routed to D202-12 and is lower than the current from R1238, which is routed to
the currents in R1238 and R1244 are equal.
input (10) of flip-flop D207. The reset input (13) is H, therefore
set
input (13) of D207 are made logic L
reset
divide-by-two stage in this mode because the
single-shot trigger.
a
input (10) is H and inverting output
set
via
set and reset inputs are both
H when the MTB sweep
logic L. Therefore the current from
a t
output D208-1 is L and the
gate
2-2 1
diodes V294 and
a t