Micron Circuits

[Dodgy Geezer]

Ah - I didn't think of 270 deg pots!

Chased the signal through to next stage - found a poor transistor connection - soldered it - another pulse came up.

I still haven't got the full set, so there is still a problem. I am unimpressed with the trimmer pots I used to set things up - the sliders don't seem reliable. I'll pick up another (slightly) better set and try again in a few days... Thanks for all the guidance so far - It was really helpful...

[Dodgy Geezer]

I now have 4 nice negative going pulses, after hitting the trim pots a lot. And I can make the gap between pulses vary smoothly. What I haven't got is a fifth pulse. The last 4124 seems to receive a pulse from the third one, but does not fire.

I note that the collector of each 4124 is connected to the +ve rail via a 5k pot, but the last 4124 is not - because there are only 4 channels on the encoder board. If there were 5 or more, that connection would happen. I further note that, at the end of the 7 half-shot stages, there is a spare 4.7k resistor which would connect the last collector to the +ve rail if all 7 channels were populated.

Should I connect the 4th 4124 collector to the +ve rail via this resistor? The diagram below shows part of a typical 4124 half-shot stage, but for the last 4124 the bit in Red is absent. Should I add the part marked in Green? The PCB seems to suggest that is what was intended...

TEST.jpg (5.55 KiB) Viewed 2217 times

[Pchristy]

Yes!

But it should go to the collector of the transistor, not the emitter as you've drawn it!

[Mike_K]

Sorry to be late to this thread. I couldn't find the scan for the early PL-7D transmitter schematic with a discrete encoder, but I found the PL-6D schematic, which I believe (from memory) had a very similar encoder to the early PL-7D. It uses BC213 PNP transistors, your sketches show NPN transistors, but in principle, they operate the same. I'll have a look through my instruction/manual box, I know I have them somewhere, but I may not have scanned them.

[Dodgy Geezer]

But it should go to the collector of the transistor, not the emitter as you've drawn it!

Ah - you spotted the deliberate mistake, then. I didn't!

I never understood what was going on inside transistors - I'm happier with valves, and i don't know much about those either. But the encoder board seems to be working now. If I draw up the half-shot stages, we will have a complete schematic for it.

Onwards and upwards to the RF board. It's odd to be working on what feels like a new Micron kit - but 50 years too late...

[Dodgy Geezer]

I couldn't find the scan for the early PL-7D transmitter schematic with a discrete encoder, but I found the PL-6D schematic, which I believe (from memory) had a very similar encoder to the early PL-7D.

Hello, Mike! Your schematic is different to mine - my encoder board doesn't have trim pots and has a darlington pair at the output end. the RF board uses a BSX81. Give me time and I'll draw mine up. The Tx box is different as well, with a jack socket charge point where the ring for teh neck strap usually goes...

[Dodgy Geezer]

My initial drafing of the RF board. I was going to test it, but as soon as I twiddled the ferrite slug, it collapsed in a heap of dirt. So I need to order another one, and hope that it's an appropriate permissivity, or however they measure these things...

[AndyS]

I finally found my Micron PL6D board as removed before the 2.4 GHz conversion. Not sure if the pics will be any help to you, but was working ok at the time of removal.

[Dodgy Geezer]

Andy, Thanks for the input. Not of direct use, I'm afraid, as it's a pl-6d, but interesting nevertheless. It gives me a clue as to how far the ferrite slug should go in!

I see that the board has the encoder and the rf sections on the same pcb. Different electronics again!