Learning Debugging from the ground up

General rules and hints to succesfuly bring back that old pedal to life
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Post by multivir »


I've built some effects and an amp out of kits in the past and recently wanted to build some vero board stomp boxes.
I tried to build two, but none of them worked. And while I think I can solder (hey, my cables work! :-) ), I don't have the knowledge to debug a vero board project (or anything related to schematics).
So... I have to gain some insights to make my pedals work. Naturally, I've read the Geofex article on fixing broken pedals, but I need to dig deeper.

Is there a good book or internet resource on how to learn to debug guitar pedals by reading schematics and measuring components? While I can measure resistors, I can't really tell if my caps are working fine. I don't know if I need any other tools like a signal generator or oscilloscope to do the job or if there are other methods - in other words: how do I get the knowledge needed from the ground up?



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Post by multivir »


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Post by DrNomis »

You could try browsing the threads in this section, for tracing out the signal path of your builds you can make what's called an Audio Probe, when tracing out the signal path of your builds, work your way backwards from the output socket back to the input socket till you hear a signal and note where you get a signal, then trace back towards the output socket and note where you lose signal, between those two points will be the cause of the loss of signal, above all be patient, keep your cool and take your time, and you'll eventually get your builds working.....hope that helps...... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.

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Post by R.G. »

Like so many things in life, being able to debug circuits is a journey, not a destination. I hacked on simple circuits in my teens, got two degrees in EE, then spend a few decades designing and getting designs released into manufacturing. I still pick up new debugging hints and tricks from skilled repairmen. Being able to debug anything, any time, is a lifelong ambition.

At the bottom of debugging is the necessity to understand what the circuit should be doing, perhaps on a part-by-part basis. Until you can do that, you don't know if what you see from the instruments matches the ideal operation well enough to be working. So debugging can really only proceed to the limits of your understanding of what the circuit does, not only overall, but part by part.

Some things are always necessary: Ohm's law is the biggie. Knowing that if the power supply isn't providing the right voltages and currents nothing else will work right is another. Beyond that, knowing what the intended DC conditions are on the active devices or better yet being able to deduce them from the schematic (or, another step up, tracing the circuit) is a huge step. If you don't know Ohm's law backwards, forwards and in several of the side dimensions, you can't progress to understanding what's happening in the circuit. Not understanding the power supply conditions will keep you from seeing if the circuit operation is right. And then there's the never-ending learning about what this new active device is supposed to do so you can see if the one in front of you is doing it.

It's a long journey.

I hope. :D

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Post by DaveKerr »

Make a probe to see what's happening at each point of the circuit
... multiple LFO waveforms (saw up, saw down, triangle, square); a more flexible envelope with attack/release controls as well as inverted envelope. I am afraid it will have more knobs than the TGP annual convention - frequencycentral

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