Service Documentation; Circuit Description; Timing Circuit - Philips PM 5775 Manual

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SERVICE DOCUMENTATION
VII. CIRCUIT DESCRIPTION
A. TIMING CIRCUIT (Fig. XIV-5)
Socket TRIGG/GATE IN, P1, accepts either trigger pulses or gate signals.
A. Trigger circuit
Diodes Z201 and Z202 are connected as a current switch and voltage limiter.
Transistors Z203 and Z204 form a Schmitt trigger circuit.
When switch REPETITION TIME is in position TRIGG. OR SINGLE SHOT — or
if switch CONT. GATED, S6, is in position GATED — Z204 is conducting and
Z203 is cut off.
Then the Schmitt-trigger is switched over by the trigger or gate signal applied to
socket TRIGG./GATE IN, PI.
Switch REPETITION TIME, S1, in position TRIGG. or SINGLE SHOT.
In this position switch CONT. GATED, S6, is short circuited by switch S1.
Switch REPETITION TIME, S1, in one of the time positions.
In all these positions, switch SINGLE SHOT, S5 is short circuited by switch
REPETITION TIME, S1. When switch CONT. GATED, S6, is in position GATED,
transistor Z,203 is cut off because the cathode of diode Z202 is connected to —20 V
via R203 and R204. However, a positive gate pulse supplied to socket TRIGG./
GATE IN makes Z203 conductive and, consequently, the Schmitt-trigger switches
over. This situation remains maintained as long as the gate pulse is present.