How to Troubleshoot pedalSHIELD MEGA

6 years 2 months ago - 4 years 9 months ago #1228 by Ray
This guide will help you to find and fix any issue with the pedalSHIELD MEGA hardware.
As an introduction, I have to say that 99% of the problems are due to silly mistakes that can be fixed with a careful visual inspection (take your time).

Before doing any serious troubleshooting just try to re-touch with the soldering iron ALL the solder joints, it is pretty easy to get a (disconnected) cold joint, especially in the header or op-amp socket (also try unplugging and plugging the op-amp). Take some time an re-heat the components joints to have perfect smooth connections.

Top 4 Silly Mistakes:
  1. Guitar connects to the right and the amp to the left hand side jack connector, like:
    :ampvox: <- :pedalmxr: <- :guitarsg:
  2. Make sure that the RV1 trimmer is in a good position. This trimmer resistor adjusts the level of the guitar signal going into the pedal. Having it in the middle position (the notch facing up) is a good starting point for any guitar, then you can go a bit clock/anti-clockwise to get a louder signal but not clipped.
  3. Electrolytic Caps or op-amp placed wrong: Have a look to a good PCB in high resolution and check that you have yours in the right orientation.
  4. Check any short circuit between nearby pads and check that all solder points are good.


Once all the things above are checked, take again your soldering iron and re-solder again all the joints (you can apply some extra solder if needed). This will fix any dry joins. This action takes a minute and solves a lot of problems. Don't forget the pin headers and also un-plug and plug the op-amp into the socket again.

Now, the best way to troubleshoot the pedalSHIELD MEGA PCB is following these 4 steps:

1. Check the power supplies: There are 3 test points on the PCB labeled as GND, +2.5V, and +5V. Using a multimeter make sure that you have there the right voltages at those points. Also, check that the op-amp is correctly powered (GND on pin 4 and +5V on pin 8 ). Additionally, check that you have the voltages of the image below:

2. Check the output stage: You can load the sine-wave generator program. It only uses the output stage independently if the input stage is wrong. If it works you can be sure that the second 1/2 op-amp area is good.
The sinewave generator code is here: www.electrosmash.com/forum/pedalshield-m...rduino-mega-2560-adk

3. Check the input stage: Be sure that the trimmer VR1 is in a "medium" position, you can adjust it better later. Load a clean/volume pedal and check if you are able to get it working. Note that it is mandatory to have the sinewave code working before trying the Clean pedal.
The Clean pedal code is here: www.electrosmash.com/forum/pedalshield-m...5-clean-guitar-pedal

4. Check your Arduino MEGA board. Sometimes there are some dodgy PCBs that do not work properly and can drive you crazy.
Load a simple code to blink the LED: www.electrosmash.com/forum/pedalshield-m...blinking-led-program

4. Use the pedalSHIELD MEGA Monitor program: This code will show you the status of all the switches, LED, push-buttons, ADC, etc It will give you a good idea of what is not working properly.
The Monitor code is here: www.electrosmash.com/forum/pedalshield-m...lshield-mega-monitor

As a tip I can to say that 99,9% of the errors are due to some connection is wrong or some component is misplaced. From previous experience building dozens of pedalSHIELDs they always work straight away from soldering correctly, but we are all humans and we all make mistakes.
  • If all the above fails, just carefully component by component that it is well placed and orientated, don't take anything for granted.
  • If you can borrow another pair of eyes to have a look at it, do it. Sometimes others can easily see things that we are passing over.
  • If you have an oscilloscope and a signal generator (I use Visual Analyzer) you can trace a sinewave from the input jack -> op-amp input -> op-amp output -> input ADC. You can also trace the output signal from the Pi Zero PWM outputs to the op-amp, etc...
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5 years 11 months ago - 5 years 11 months ago #1374 by Sonstwer
Hi,

i got some strong noise problem,

i bought this Power Supply
DC 500mA 1A 2A 220V
www.amazon.de/gp/product/B01EWI95RY/ref=...00_s01?ie=UTF8&psc=1

that helped reduce the noise a little bit, but not enough
i also turned the RV1 trimmer without any (strong) effect

i will re-check every soldering tomorrow (or soon),
is my chip set in right? are there other things i could have done wrong?

do i have to (somehow) ground the pedal?

Edit: the only thing i realize i did a bit differently was that i made the led much shorter (i thought it should be very close to the shield as well and only realized later)

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5 years 11 months ago #1375 by Ray
Hi Sonstwer,

the only thing i realize i did a bit differently was that i made the led much shorter (i thought it should be very close to the shield as well and only realized later)

That won't be a problem, the LED legs length has no effect over the sonic performance.

i bought this Power Supply
DC 500mA 1A 2A 220V
www.amazon.de/gp/product/B01EWI95RY/ref=...00_s01?ie=UTF8&psc=1

Looks like a good power supply, as far as the Arduino MEGA is happy with it, the shield will be happy too.

I have compared your board against mine and all seems to be in place.

Have you tried just using the sinewave generator, that code should be pretty clean and it should not create much hiss noise.

Could you describe the noise? is more like a hummmmm or like a noise hisssss.

The Arduino MEGA is not the best piece of hi-fi but the sound quality should be at least as good as the one we have in the MEGA video in youtube, we did not apply any noise reduction.

Sometimes ground loops could be a problem, try to connect the arduino DC power supply close to your amplifier mains connector (also disconnect it from the computer (no USB))

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5 years 11 months ago - 5 years 11 months ago #1379 by Sonstwer
Hi,
Today I checked all soldering points again and repaired every single one of them that didn't look very nice.

The power supply I used is crap

I made a video comparison with a battery pack I got myself, not with the effects you proposed, but I'm not near my computer to change effects right now.

The sound distortion is quite good to hear



Which of the shields you have at electrosmash sounds best?

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5 years 11 months ago #1380 by Sonstwer
So,
i was finally able to change the sinewave generator.

i found a funny bug (or maybe an indicator that i indeed did something wrong when i build my shield)

what do you say?

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5 years 11 months ago #1382 by Ray

Rendering Error in layout Message/Item: array_keys(): Argument #1 ($array) must be of type array, null given. Please enable debug mode for more information.

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5 years 3 months ago #1628 by lreinhart
The buttons and switches all work. The OLED works. The Sin Wave program sounds nice. The value for the ADC is around 32704; that is close to max as I understand it. I will take a close look at the circuit board and components tomorrow, but if this sort of thing has been seen before it could save me time.

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5 years 3 months ago #1629 by Ray

The value for the ADC is around 32704; that is close to max as I understand it

www.electrosmash.com/images/tech/pedalsh...d-mega-schematic.jpg
with nothing connected to the pedal (just power) make sure that the op-amps pins 5,6 and 7 are around 2.1 to 2.5V approx.
Also, check that the ADC A0 pin is around 2.1 to 2.5V

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5 years 3 months ago #1632 by lreinhart
Fixed up some insufficient solder joints and found that using batteries is the only way to keep it quiet. I am using two 2500 mah lithium cells that produce 8.25 volts and there are no noise problems at all. I am not seeing a big difference between the effects on and off, but there is a difference. The sound is very clean though. I wonder if I need a higher voltage, the next cell would take me a bit over 12 volts fully charged. The bit cruncher, for example does nothing until I reduce the number to 9 then all off a sudden it gets real loud. I haven't done anything with the pot, it is still in the middle position. So far I like the Chorus and Vibrato the best. I will start messing with the programming soon.

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5 years 3 months ago #1633 by lreinhart
I adjusted the pot so the output is the same for both switch positions (pass through, effects) and I think the battery is fine. My favorite is still chorus and tremolo, but I will try each for awhile and make a multi with my favorites. I see the VUE meter in some pictures, but not in any of the published code. Does the Mega not have enough power to handle it?

I like the Mega shield, it meets my expectations.

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