Author Topic: Tutorials on how to troubleshoot?  (Read 115 times)

Jefe

  • Diode Destroyer
  • *
  • Posts: 46
    • View Profile
Tutorials on how to troubleshoot?
« on: March 14, 2019, 04:11:31 AM »
Can anyone point me to some learning material or tutorials on how to troubleshoot? I've got multimeters, and a test probe, but I'm no good at interpreting what I find. Thanks!

JackSkellington

  • Stompbox Star
  • ***
  • Posts: 222
    • View Profile
Re: Tutorials on how to troubleshoot?
« Reply #1 on: March 14, 2019, 04:38:54 AM »
I don't know if we can write a tutorial, but probably you can find some tips. And even some tips about the building, check everything double or triple.
Measure your resistors before and after to solder, read the code on the caps, use the test of the continuity for wires, check the positions of the parts, etc...

To probe the cirucuit you should follow the signal looking at the schematic, and of course, it depends from the schematic.
«Just because I cannot see it doesn't mean I can't believe it»

somnif

  • Electron Doctor
  • *****
  • Posts: 1299
    • View Profile
Re: Tutorials on how to troubleshoot?
« Reply #2 on: March 14, 2019, 05:14:00 AM »
First steps -

Double check your wiring and connections. Make sure positive is going to positive, make sure grounds are connected, make sure you have the instrument plugged into the "In" jack, that sorta thing. Make sure you don't have any obvious solder blobs bridging things. Make sure you're not shorting on the backs of pots or the enclosure. Make sure ICs are the right way round, diodes/transistors/electrolytic caps are oriented right.

With an audio probe, power up the circuit. Plug in something that can make sound into the input (I use a tiny 2 transistor white noise generator). Connect your probe to your amp (along with its ground). Poke at the input, do you hear sound. Poke at the next component in the audio path, still hear sound? On and on, one side of a component then the next. If you find a spot where there should be noise, but you're not getting any, its suspect. (reading the audio path from the schematic takes some practice, don't be afraid to ask for help)

For checking voltages, power up the circuit, attach the black lead of your DMM to ground, and poke the red around. Check +9V (or whatever the supply voltage is), the ground (usually 0V), each pin of ICs, each pin of transistors. Look up the build docs and schematic, figure out what the power and ground pins of the ICs are to verify things look good there. The build docs may also have "expected" voltages to compare to. (Interpreting "wrong" values takes some practice, don't be afraid to ask for help)

Pictures help if you need to ask the board for assistance. Top and bottom, as clear as you can get them. Sometimes its as simple as a fresh set of eyes realizing you put a 1k resistor in place of a 1M, etc etc. (Our yees often blind themselves to somethign we've been staring at for hours, don't be afraid to ask for help)

And, always, don't be afraid to ask for help!

Oh, and take breaks, troubleshooting WILL frustrate you, and we don't want you gnawing on your pcb's in a blind fury.  ;D

midwayfair

  • Electron Doctor
  • *****
  • Posts: 6952
  • Jon P
    • View Profile
    • Midway Fair
Re: Tutorials on how to troubleshoot?
« Reply #3 on: March 14, 2019, 06:11:52 AM »
http://www.madbeanpedals.com/forum/index.php?topic=902.0

https://www.reddit.com/r/diypedals/comments/23yroq/some_friendly_reminders_about_getting_effective/

I hate to say it, but interpreting what you find is mostly just experience and comparing with known working examples unless you study how circuits work in general. Like you'll recognize that op amp voltages are off if they don't match typical voltages.
« Last Edit: March 14, 2019, 06:13:43 AM by midwayfair »
Myself's music & things I make: http://jonpattonmusic.com. My band: http://midwayfair.org. PCBs of my designs from: http://www.1776Effects.com (Bearhug Comp & Cardinal Harmonic Trem); http://www.jmkpcbs.com (Hamlet+ delay & Blue Warbler envelope vibe); Snow Day OD/Flabulanche: www.madbeanpedals.com

Jefe

  • Diode Destroyer
  • *
  • Posts: 46
    • View Profile
Re: Tutorials on how to troubleshoot?
« Reply #4 on: March 14, 2019, 06:31:02 AM »
Thanks guys. These are all good places to start. And yeah, I know it mostly comes with experience, but it's still overwhemling simetimes just knowing where to start looking. Having some kind of checklist to go through helps. And in the end, it really comes down to re-checking everything, I guess.

I've got a small pile of builds that I need to debug, but I'll give you a basic example:
The pedal passes sound in bypass, standard 3PDT bypass switch. When engaging the effect, no sound, no LED.
Double checked my power connections, power is getting to the board, not reversed, etc. Check the voltage at the (board mounted) LED, I'm reading millivolts.
Using my test probe, I get a signal at the input jack in bypass. Engage the effect, I lose the signal at the input jack - what does that mean?? Do I have a short to ground somewhere, or?? This is where I get stuck. Again, I'll just have to dig in and start double checking all my wiring, solder joints, etc. I'm just hoping to at least rule some things out?

HamSandwich

  • Solder Ninja
  • ****
  • Posts: 346
    • View Profile
Re: Tutorials on how to troubleshoot?
« Reply #5 on: March 14, 2019, 10:56:04 AM »
Between here and DIYSB, you can read a couple debugging threads a day. There's usually a couple odd ones, but it's surprising how often similar problems occur. You can learn a lot from other peoples mistakes  ;D