A baby 10 turned into an oscillator.. supposed to be a christmas present, now its being cranky.. HELP!

ugh… so, been working on this for two weeks, was supposed to be a Christmas present, and I’m now stuck. Its a simple concept. speed up the clock to a 4017 and you get an oscillator. its a bit like a sample and hold I guess. so I built this circuit (I thought) exactly on a breadboard with bipolar power and a tl074 integrator to turn the output into a triangle waveform and it worked great. the whole idea is a battery operated toy that is like a light Theremin meets an APC. to which the breadboard design achieved. I sketch it out, plot it on kicad using a 2262 and lm386 for use with battery power, ordered some pcb’s and assembled. and its garbage! I think I have a bad diode, or possibly a bad pcb? (its from JLCPCB) why I’m thinking its a bad pcb, I still got sound out of the speaker with the dc decoupling cap, and the pull down resistor removed. which is supposed to remove all paths to the speaker, but yet i still get sound… also, the clock reacts like the pot is a log resistor, not linear. also with the scope, and everything connected, the capacitor is discharging, through the pull down resistor (I think). I’m going to try and ground the pots and remove that resistor, and see what happens, but other than that, I’m stuck… ideas?


Start with grounding and continuity of grounding. Then look at power supply and local noise.

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First check all power connections.
Do all ICs get the power they need? Are all of them connected to gnd properly?

If you’ve got a scope, you should be able to trace all relevant signals.
Start with the clock. Is it running?
Next have a look at the input of the counter. Does it receive the clock?
Then look at the outputs of the counter. Do they produce 0’s and 1’s?
Next check whether any pulses arriving at the integrator are integrated.
Finally check that the LM357 produces an output proportional to the signal on its input potentiometer.

Note: if any of the signals is missing, that could be because the PCB lacks some connection, or the signal is not produced by its source. So also check the ‘wiring’.

If you walk through the diagram systematically, you should be able to find the fault.
Oh yes, and DO NOT MAKE ANY ASSUMPTIONS. Check everything!


Fixed… mostly anyways… I don’t know if if was a bad pcb, wire, solder bridge maybe? I couldn’t find anything, so I started from scratch on a new board with IC sockets as opposed to just soldering them to the board, checked output at each stage while I built it. everything was good, except the integrator wasn’t working in a way that sounded good, so I just bypassed it. so was it the integrator? maybe… point is it worked :slight_smile: thanks for the help folks!