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TOPIC: How to Troubleshoot pedalSHIELD MEGA

How to Troubleshoot pedalSHIELD MEGA 2 months 3 weeks ago #1925

  • Tigibus
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Here is an image of my board(I just change C2 6.8nF cap for a better one recently, I suspected it was the problem but nothing changes).


EDIT : Are you sure of your TL972 ??? Do you test them ?
Last Edit: 2 months 3 weeks ago by Tigibus.
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How to Troubleshoot pedalSHIELD MEGA 2 months 3 weeks ago #1926

  • Ray
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Hi:
Thanks. But all the Voltages mentioned before does not fit with yours. After R2 I found 1.40V like on PIN 5 but 2.4V at 2.5V area before R2.
I used a lot of time the image from your link to double check all the tracks on the PCB and where are supposed to be the different components and it's exactly like mine. I can make a Copy/Paste for your photo and my board.

If you have a big drop after R2 is because too much current is passing through that R2 resistor.
Could you unplug the op-amp and measure again? just to check if its the op-amp the one which is taking that extra current or maybe your pedal is oscillating.
EDIT : Are you sure of your TL972 ??? Do you test them ?
I cannot read the TL972 legend on your image but I guess that it's difficult to read with the camera.
I do not check the chips, I get them from one of the the best suppliers in the US (Mouser) and send them out directly.
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How to Troubleshoot pedalSHIELD MEGA 2 months 2 weeks ago #1928

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hi, thats very weird, look my image below:

Untitled_2019-08-24_2019-08-27.png


- If you remove the op-amp, not current will be flowing into the pin 5 (i2=0)
- Also, C1 will not allow any DC current to flow through it (i1=0)

So if you have 1.21V on R2, where is that current going to?
Are you sure that you have 2.5V at the voltage divider (make sure that this 2.5V are stable, not jumping).
If you are powering the circuit using USB its normal not to have 5V (you will probably have 4.7 or 4.8V) so the divider will be 2.4 or so.

Could you try to pore the Arduino using a standard 12V supply? maybe the 5V regulator on the Arduino board is not working properly.
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How to Troubleshoot pedalSHIELD MEGA 2 months 2 weeks ago #1930

  • eshoji
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Hi,

I have received my pedalShield MEGA from you yesterday in Japan. Thank you very much for your attractive great products!

I am using 9V DC supply. First I experienced the same issue of 1.2V on R2. So, I switched to use volt meter that has higher input impedance (FET electronic tester). I have 2.4V at pin5 now (no TL972 seated on the socket). The question, where is that current going to? There will be current flows across the internal resistance of the volt meter that doesn't have higher input impedance, because R2 has very high resistance value of 1M. I think this awareness could be useful for people who are facing unexpected lower readout volts. I assume that Tigibus'pedal may be working correctly...

Thank you,
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How to Troubleshoot pedalSHIELD MEGA 2 months 1 week ago #1952

  • Dena
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I have some problems with the I2C bus, can I connect more peripherals to the bus? or is it limited in some way?
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How to Troubleshoot pedalSHIELD MEGA 2 months 6 hours ago #1960

  • Ray
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I have some problems with the I2C bus, can I connect more peripherals to the bus? or is it limited in some way?

The II2 bus is not limited in any way, you can use other peripherals without a problem. Just make sure that you are not using the same bus address (the OLED screen has the address written on the back of the PCB)
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