How to Troubleshoot pedalSHIELD MEGA

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.

• If you only have problems with the OLED display, have a look to the OLED troubleshooting topic: www.electrosmash.com/forum/pedalshield-m...8x64-troubleshooting

Top 4 Silly Mistakes:

1. Guitar connects to the right and the amp to the left hand side jack connector, like:
   <- <-
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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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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