Hello. I recently built a Geiger Counter from the schematic below. I am trying to self-tech myself electronics. I need someone with some experience to tell me what is going on in the top left corner of the schematic. Specifically D1, IC1-a and IC1-b. It is a hex inverter that sends out pulses to the transformer. The potentiometer adjusts the pulse width to adjust the voltage. I can't quite figure out what exactly is going on the top left part. I understand the rest though. Thanks in advance!

the schematic....
http://www.freeinfosociety.com/electronics/schemview.php?id=2064

 

I redrawn the part of the diagram.
I hope that know you can see how this part of a circuit work.

If you have any questions, feel free to ask.

 

I think the diode confuses me more than anything. I would think that any pulses from the Hex Inverter would be blocked by the diode.

 

It is a simple two inverter oscillator feeding a voltage booster. The diode in question is not a big player. It might even be able to be eliminated.

It is part of a voltage divider created by R3, R8, and R2, and adjustment of R8 will cause the base line voltage of IC1c and IC1D to vary. Add the signal being injected this would cause narrow pulses as C2 is going to ground on the other side. My best guess is it is a signal shaper, helping to create narrow high pulses to the MOSFET (narrow ground pulses to the inverters).

Personally I would say this circuit is way overcomplicated at this point, but they had the spare inverting gates, so they decided to use them. It is a kludge, the circuit is designed to create high voltage feeding into J1. It could be made much, much simpler.