I made a clock driver that counts pulses from 120VAC. It doesn't work well, it runs very fast. It seems to be getting spurious pulses from somewhere.

I want to investigate and fix the driver and am thinking an oscilloscope should be able to tell me what is going on with my device.

I don't own a scope and have never used one. So I want to ask, am I on the right track? Will a scope show me 60 Hz 1 volt pulses together with (probably) the presence of extra random pulses? Will I be able to figure out how to use the scope in a reasonable time?

And I'm wondering if the cheap scopes on Amazon (couple hundred dollars) might be OK for a task like this.

I tinker with electronics but have been a newbie for the last 60 years. Always willing to learn.

 

Before we consider the scope option, show us the circuit schematics of your clock driver.

 

I made a clock driver that counts pulses from 120VAC. It doesn't work well, it runs very fast. It seems to be getting spurious pulses from somewhere.

I want to investigate and fix the driver and am thinking an oscilloscope should be able to tell me what is going on with my device.

I don't own a scope and have never used one. So I want to ask, am I on the right track? Will a scope show me 60 Hz 1 volt pulses together with (probably) the presence of extra random pulses? Will I be able to figure out how to use the scope in a reasonable time?

And I'm wondering if the cheap scopes on Amazon (couple hundred dollars) might be OK for a task like this.

I tinker with electronics but have been a newbie for the last 60 years. Always willing to learn.

Any scope could handle this. An old analog scope is far easier to use for a beginner, but digital storage scopes can do things an analog scope never imagined, like capturing one time events.

 

Before we consider the scope option, show us the circuit schematics of your clock driver.

OK, give me a bit of time, but it isn't going to help. The breadboarded version worked perfectly, but now it's on a PC board, it doesn't.

 

OK, give me a bit of time, but it isn't going to help. The breadboarded version worked perfectly, but now it's on a PC board, it doesn't.

Classic!
It works on the breadboard but not on the PCB.

 

OK, give me a bit of time, but it isn't going to help.

Our concerns is the safety of probing a circuit that is powered from the 120Vac mains.

 

Our concerns is the safety of probing a circuit that is powered from the 120Vac mains.

How to proceed, then?

 

Our concerns is the safety of probing a circuit that is powered from the 120Vac mains.

Which argues for a battery (it isolated low voltage supply) operated scope so there is no grounding issue. A cheap one like this might do it.

 

Which argues for a battery (it isolated low voltage supply) operated scope so there is no grounding issue. A cheap one like this might do it.

Did you mean this one? The link is not specific.

 

Hi,
If it worked OK on a breadboard, you have made a mistake on your PCB.
Please show us some detailed pictures, both sides of your PCB.
Defense rests............

 

Use an isolation transformer (1:1) That way you're isolated from mains power.

 

Hi,
If it worked OK on a breadboard, you have made a mistake on your PCB.
Please show us some detailed pictures, both sides of your PCB.
Defense rests............

Yes, agreed. But I am too bashful to show you my crappy soldering. Also I don't think I could show the details well enough to be sufficiently diagnostic. I have gone over it myself several times with a magnifier, and made new circuit diagrams off the PCB, and checked for agreement with the original circuit diagram. No revelations so far.

One strategy is to make a second one....

But using a scope might work. Could be useful too if a component has failed.

 

Yes, agreed. But I am too bashful to show you my crappy soldering. Also I don't think I could show the details well enough to be sufficiently diagnostic. I have gone over it myself several times with a magnifier, and made new circuit diagrams off the PCB, and checked for agreement with the original circuit diagram. No revelations so far.

One strategy is to make a second one....

But using a scope might work. Could be useful too if a component has failed.

Being bashful on AAC costs you nothing.
Many a problem has been solved on AAC forums by just showing a photograph of your circuit and board.

 

Being bashful on AAC costs you nothing.
Many a problem has been solved on AAC forums by just showing a photograph of your circuit and board.

OK, thank you - that would be amazing.

Working on it....

 

OK, thank you - that would be amazing.

Working on it....

Here is the schematic. (Edited)

 

Here is the schematic.

View attachment 363182

And here are the photos.





Note that an extra capacitor is present (at the optocoupler). It is redundant. The device runs the same with it and without it.

 

Isn't this the same schematic from your railway clock?
I thought you had that working.

 

Isn't this the same schematic from your railway clock?
I thought you had that working.

Correct. It's working, but not working right. It cycles in around 40 seconds instead of 1 minute. The pulses also seem to be inconsistent. It speeds up when the load is activated. Those are some rough observations. I need better gear to know what it is actually doing.

The breadboard worked exactly right, but not the PCB. So there is a wiring error or short or maybe a bad part.

 

Was that 24 volt module also located on the breadboard when working correctly?

 

Was that 24 volt module also located on the breadboard when working correctly?

The power supply? Yes. Here is a pic of the breadboard.


I took several detailed closeup pics of the breadboard to make sure I could go back and see how everything was connected. As far as I can tell, the PCB is wired the same.