Technical, Techniques, Hints, and Tips > Radio Equipment
Old Micron data request...
HMS Invisible:
If you have a suitable resistor, like 10 to 100 ohm you can put that in series for safety as you up the voltage.
If it doesn't burst into life there is something wrong in the circuit or the soldering. It's pretty basic stuff that I've used.
I'd be drawing ( by hand) the astable multivibrator.
Double check the function then centralise pots without desoldering. If the combined length of the pulses > the frame it goes haywire. However I think it's just component values that don't work at low voltage or an error.
I'd be working off a full schematic, double checked!
dodgy geezer:
Haywire would be nice! All I can detect on the scope is 0v, going up to 5v occasionally as I try each land. Do you think that more volts are needed? It would have been run at 9.6v originally, but the transistors ought to start at about 3v...
A full schematic would be great. Maybe I'll draw one...
HMS Invisible:
--- Quote from: dodgy geezer on August 12, 2025, 06:29:32 pm ---Haywire would be nice! All I can detect on the scope is 0v, going up to 5v occasionally as I try each land. Do you think that more volts are needed? It would have been run at 9.6v originally, but the transistors ought to start at about 3v...
A full schematic would be great. Maybe I'll draw one...
--- End quote ---
No, the voltage was an accidental misdirection and you should be OK at 5.
The voltages at the astable part will point you right to the problem if you use the diagram in the link below for number reference.
The astable timing capacitor colour codes, diode check of the transistors, and dmm measurements of its resistors is enough.
If there is a component missing it won't work.
https://www.electronics-tutorials.ws/waveforms/astable.html
dodgy geezer:
I will need to do the schematic. I wonder why there are a pair of what look like diodes in the MV circuitry....
HMS Invisible:
The two extra diodes conduct to clamp the negative kick to -1 volt.
The clue to what is going wrong will come from the Vc, Vb state at which the oscillator transistors settled at, and if diode tests say the transistors are OK.
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