How the agfa camera xenon flasher circuit works!

HOW THE CIRCUIT WORKS
The circuit is turned on by a “start” button that puts a small DC voltage (from the 1.5v DC supply) into a 100u electrolytic. The voltage across this electro is passed to the base of an NPN transistor and this causes the collector-emitter leads to have a low resistance. This turns on a PNP transistor and the PNP transistor delivers current to the main oscillator transistor. The oscillator stage now looks almost exactly like the oscillator stage of circuit 1. The circuit will start-up quickly and the operator will not have time to release the “start” switch before the waveform on the collector of the oscillator transistor is able to pass spikes of energy into the 100u via the diode.
This will give the electro added voltage so that the circuit stays on long enough to charge the 120u 330volt electrolytic for the flash tube.
The 100u in the time-delay circuit (also called the start-up circuit) is gradually discharged by the 330k (and also the 220k) and these are designed to turn the circuit off completely.
An indicator LED is included in the circuit and you will notice it is up-side-down to what you would expect.
As the voltage across the 120u electrolytic reaches 260v, the magnetic energy in the transformer is not required by the electrolytic and larger negative pulses develop. These pulses are fed to the LED via the 150R resistor and the LED begins to illuminate.
The circuit shuts down to absolutely zero current via the 330k bleed resistor removing all the voltage from the 100u electrolytic.
The first transistor is said to be in a ‘high impedance” arrangement so that it bleeds very little from the 100u while it is keeping the rest of the circuit active.
The 150R on the emitter is forming a dual task and needs describing.
The aim of the circuit is to get as much charge into the 100u as possible so that the circuit stays on for as long as possible.
When the circuit turns on, current flows through the 150R and this causes a voltage to develop across it to raise the emitter. This means the base will be higher and thus a higher voltage is needed on the base to keep the transistor turned on. This is not a problem but the advantage is the transistor draws less current (bleeds less current) from the 100u and so the delay time is extended.
The other (and main) reason why the resistor is added is to raise the voltage on the collector of the first transistor so that the second transistor can turn on the oscillator transistor.

S:electronicsuite.com