Most likely things wrong if a pedal doesn't work

[R.G.]

We have a quorum of neophytes, so I thought maybe it would help to run this. It's laced through "what to do when it doesn't work" and the Effects Debug Page at GEO, but the most common thing new builders do is ignore the helpful background information and ask here instead.

So - your brand new effect build doesn't work. Bummer. Here's a list of the most likely things to be wrong with it. This list is gleaned from personal experience as well as over ten years of helping people get new effects running.

- No power to the circuit; the battery or power supply may not be connected in spite of what you think the wires do, or may be reversed.
- Component pinout wrong, especially transistors of all kinds. Go download the datasheet from the net and say a "thank you" for the net providing you access to all of that.
- Component inserted wrong or backwards
- Wrong value resistor, capacitor, zener diode, etc. The values can be hard to read.
- Bad soldering. Solder joints that are not making connection, blobs shorting pins and traces together, loose solder balls between pins, you name it, it's there.
- Bad circuit boards: PCB etching problems, incomplete cuts on vero board, shorted traces, open traces, boards cracked by being cut. These can be hard to find.
- Incorrect wiring of the off-board leads, or broken wires.
- shorts between wires and/or PCB and the case

Finding out which of these things is wrong is done by both tracing out connections and wiring visually, and by measuring voltages inside the circuit. That's why I posted the info I did in "What to do when it doesn't work". That set of dance steps verifies power to the board, verifies power to each component, and then verifies that the working voltages are approximately correct. It's a very, very effective set of steps to find out why it just doesn't work. Most of the time it's all that's needed to point to a fix.

What's least likely to be wrong is a new, but bad component. It does happen, but it's rare. You will sometimes find a schematic with a typo error in it, but not often. There are also sometimes errors in networks on the web. If the effect you're making has had other people be successful with it, it is very unlikely that there is a schematic or board error.

[Dragonfly]

as always, nice post R.G....should save some people LOTS of time and headaches...

i tend to start the "de-bugging" process by making sure that my ground connections are good...

AC

[newbie builder]

My debugging process thus far has started and ended with the led....I've built 5 pedals and on 4 of them I got the LED polarity wrong the first time.... (and the one I got it right on had a board mounted led so it was pretty much impossible to screw up!)

[R.G.]

I always use a resistor and battery to test LEDs before I solder them in.

This is after a run-in with a batch of LEDs that had the cathode-marking flat on the body reversed. The flat on this batch marked the anode. Took me a long time to figure out what I'd done wrong on that one. Now I test them all just in case.

[petemoore]

  Mother Nature, our friend, is cool because of her very consistant nature, she can do certain things for us, but only under 'certain' *conditions, she Can Seem MEAN because of her strict set of rules, using *'strict' in the most literal sense of the word.
  I thought there would be more secrets, but after having been a Forumite for more than 5, I've found out there really aren't any 'actual' secrets...the remaining 'secrets' are just things you don't know about yet. OR...that 'Thing' your circuit is hiding which should not be, the thing that disallows function. Whatever the conditions, they ARE there, whether these conditions are known or not is another matter entirely.
  From electron flow in an active device to capacitor 'mojo' all the real data is there, lots of it, Tons of it, then more..more...more than you can read and absorb in one hour/day/week/year/'?'
...it tends to be equational and therefore interactive with itself, so it is possible to set up a veritable plethora of 'conditions'. Understanding that these conditions are interactive...often the voltage or current is 'moving'/'flowing'...and dependant on other conditions that may move or flow...understanding ohms law is good to try, because it doesn't take bribes.

[Mark Hammer]

"Things are not always what they seem to be"  is as good a summary of what can go awry as I can think of.  To whit...

• the pinout you THOUGHT was correct isn't
• the jack/switch,chassi-cover you THOUGHT wasn't touching anything else IS
• the LED you THOUGHT was oriented right wasn't
• the pot you THOUGHT was 100% operational isn't
• the solder lug on the jack you THOUGHT went to ring connection goes to tip
• what you THOUGHT was a perfectly viable solder joint wasn't
• the solder lug you THOUGHT you were supposed to use for the battery on the wallwart socket wasn't
• the chip you THOUGHT was fine before you inserted it, was blown
• the chip legs you THOUGHT were making contact with the socket aren't
• the solder lugs in that 3x3 array on the stompswitch that you THOUGHT were oriented in a certain direction, aren't
• the wire that you THOUGHT was securely soldered to the pot or switch before you started twisting them around to fit in the box, isn't anymore
• the PCB trace that you THOUGHT provided a continuous path between point A and B doesn't
• the PCB traces you THOUGHT were isolated from each other, aren't
• the wallwart that you THOUGHT was DC (or AC) isn't
• the cap value that you THOUGHT "103" (or worse, 100) represented, isn't
• the resistor that you THOUGHT was supposed to go into that spot on the PCB isn't

...and so on.  Essentially, trouble-shooting involves going through your list of working assumptions about what IS true, and finding out which are...and which aren't.

[rockhorst]

Ohms law [...] doesn't take bribes

I'm afraid that I'm going to have to bust your bubble there. Ohms law is a mere 'fluke' if you want. A very handy fluke and all our electronics depends on it, but that's just because we have picked out materials that satisfy Ohms law to use in electronics. To convince you concider this: All of classical electrodynamics is caught within Maxwell's equations, and Ohm's law can't be derived from them. We're just lucky that electrons in a wide variety of materials (but not all!) are just bumping carts that are constantly accelerated and slowed down, resulting in a steady current, instead of just being accelerated by an electric field.

R.G. and Mark: very wise lists, basically one should run everything over twice before posting. I do swear that I do...but it's like putting down a pen, getting a sheet of paper from from your desk and when you turn back your pen is nowhere in sight, even though you are actually staring at it. True, it happens to noobs more than to pros (well, with schematics and circuits, the pen thing I think is universal)

[Mark Hammer]

Pens, socks, that $5 you could have sworn was in your pocket, your bus/transit pass just as you get on the bus, the warranty for your muffler, the receipt for the microwave that never worked once you unpacked it, and those ground connections you could have sworn you made.  I think they all go to the same place.  One of these days, I'd like to visit that place, because I'll bet it's chock full of smiling people saying "So THAT'S where it went to!"

[R.G.]

Ohms law [...] doesn't take bribes

I'm afraid that I'm going to have to bust your bubble there. Ohms law is a mere 'fluke' if you want. A very handy fluke and all our electronics depends on it, but that's just because we have picked out materials that satisfy Ohms law to use in electronics. To convince you concider this: All of classical electrodynamics is caught within Maxwell's equations, and Ohm's law can't be derived from them. We're just lucky that electrons in a wide variety of materials (but not all!) are just bumping carts that are constantly accelerated and slowed down, resulting in a steady current, instead of just being accelerated by an electric field.

No bubble to burst. Ohm's law, whether we believe in it or not, fluke or not, metaphor or metaphysical muffin, works. Whether or not you can derive Ohm's law from Maxwell's equations or not, you still get resistance as the proprotionality of voltage and current. That's what "resistance" means.

Of course all materials are not linear resistors. But we're not trying to redefine electronics into nonlinear differential equations or electron fluid dynamics here - we're trying to help newbies understand the basics.

And fluke or not, who would you pay to make resistance not be the ratio of voltage to current?   

[jrc4558]

If you think of it, the list of potential causes of malfunction in any electronic device can be narrowed down to two:
1) Contact is present where its supposed to be absent.
2) Contact is absent where its supposed to be present.

[zjokka]

I always use a resistor and battery to test LEDs before I solder them in.

This is after a run-in with a batch of LEDs that had the cathode-marking flat on the body reversed. The flat on this batch marked the anode. Took me a long time to figure out what I'd done wrong on that one. Now I test them all just in case.

I never though they would deviate from such a standard rule on diodes. Did you find diodes with leg lenghts confused as well?
Couldn't this have been a box of faulty diodes?

This sure was helpful. I have a component tester, but mostly take diode orientation for granted.
thanks

[rockhorst]

One more note on physics for R.G. 

And fluke or not, who would you pay to make resistance not be the ratio of voltage to current? 

Nobody. But that doesn't mean Ohm's law in applicable in general. Ohm's law assumes a linear relation between voltage and current, and because linearity is easy to work with, we want to use linear resistors. Ohmic's are resistors but not all resistors are Ohmic. See the loophole you fell for? 

I was just making candid conversation in a reaction to a reaction. I'm one of those noobs myself RG, you know that

[R.G.]

Hey, here's an idea. I'll post a note on the net, advertising the services of my company (TBD) to selectively violate Ohm's law for a fee. 

[jrc4558]

Hey, here's an idea. I'll post a note on the net, advertising the services of my company (TBD) to selectively violate Ohm's law for a fee. 

Need a Canadian branch to represent your company?

[markm]

If you think of it, the list of potential causes of malfunction in any electronic device can be narrowed down to two:
1) Contact is present where its supposed to be absent.
2) Contact is absent where its supposed to be present.

SImple but, very true!

[burnt fingers]

Well I'm no expert but for me, the top thing that always goes wrong is me.  User error.  Idiot with a soldering iron, here's your sign.

Scott

[rockhorst]

Hey, here's an idea. I'll post a note on the net, advertising the services of my company (TBD) to selectively violate Ohm's law for a fee.  Grin

Somehow I don't think it's gonna make you a rich man, R.G.  It's not a general rule, but a dang handy one when comes to circuitry.

[SolderBoy]

Forget Ohm's Law, try figuring out "Solderboy's Law of Perceved Sonic Mojo":

"The more scratched, dented and smelling of beer and cigarettes a piece of electronic musical equipment is, the better it sounds."

From memory, I think its an inverse square relationship.   


Actually I'll tell you the real problem with audio electronics...

Equal temperament.

Its a crock.  It defies nature. 

What were we thinking?!  I recon Bach just got greedy. (Harmonically speaking of course.)

We are just lucky that most of the first few even order harmonics are so much closer to the natural harmonics than most of the odd ones.  Otherwise PhD students really would be using Solderboy's Laws for trying to understand the valve/transistor argument and all that!

[gaussmarkov]

... and maxwell's equations don't always predict satisfactorily either.  what's with that?   

[MartyMart]

The most likely problem, is just that     "you did something wrong" !

Wrong part ... wrong connection .... read the schematic wrong

Here's a "tip"  .... never use old rescued parts ... it will drive you nuts when one of them doesn't work


.......  somewhere  !! 
MM