Unit not working, U1 pin 3 = 1V

6 years 4 months ago - 6 years 4 months ago #1235 by Charlez99
I just received & built my unit, but it doesn't work.
Significant noise and distorded sound when unit is ON, no noise when unit is OFF (dry).

I verified everything with no success;
All supplies are OK (+5 and -5V, TC1044 oscillating at around 20Khz).
LED is working and analog output stage is also working fine (tested with sinewave.ino).

Problem seems to be on the analog input stage.
All voltage on U1 are OK except abnormal pin 3 which is around 1.0V instead of 0.1V (Ref: Guide to troubleshoot...)
Different people have reported that issue with pin 3 on the forum but none have explained what was the source of the problem.

Anybody can help ?
Thx

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6 years 4 months ago - 6 years 4 months ago #1237 by Ray
Replied by Ray on topic Unit not working, U1 pin 3 = 1V

Significant noise and distorded sound when unit is ON, no noise when unit is OFF (dry).

- The power supply makes a huge difference in some boards, try to use an external 12V adapter or a better wall-usb adapter, have a look at this:
www.electrosmash.com/forum/hardware-peda...powering-arduino-due
- Also, make sure that the VR1 input trimmer is in a "sensible" position.

All voltage on U1 are OK except abnormal pin 3 which is around 1.0V instead of 0.1V (Ref: Guide to troubleshoot...)
Different people have reported that issue with pin 3 on the forum but none have explained what was the source of the problem.


Sorry, the 0.1V voltage on pin 3 is a typo (I already fix it in here: www.electrosmash.com/forum/hardware-peda...alshield?lang=en#269), the reading should be something between 0.8 and 1.0V on pin 3.
You should have 1.6V on the BIAS test point on the PCB, and then you have R2 that drops around 0.5V, so the bias point at pin 3 should be not far from 1.0V.

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6 years 4 months ago - 6 years 4 months ago #1239 by Charlez99
Ray,

I tried to power my Pedalshield from my laptop and my desktop computer (both direct or via a powered USB hub), via an external linear power supply (made with 7812 & 7912 linear voltage regulator), and also from a 9V battery. There is no difference, it's always the same. The problem must be somewhere else.

Yes I adjusted the CR1 pot using the sketch made for that purpose.

I attached a set of screen capture that shows the input & output waveform using my scope (Yellow = input signal = 440Hz sinewave from a DDS signal generator, Blue = outout signal, with PedalShield foot switch OFF & ON).






I also tried to do some resoldering using my hot air solering station, whitout success.

Thanks for correcting the typo regarding the 1V on pin3 in the troubleshooting guide, this was misleading.

PS
I've noticed something else a bit strange, the blue LED doesn't always turn ON when it should.
The 3.3V from the Due is OK, but output pin3, when ON is a bit low (around 3.0-3.1V) and seems unable to turn on the LED everytime (and blue LED requires a higher voltage than red LED).

Thanks for your help.
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6 years 4 months ago #1242 by Ray
Replied by Ray on topic Unit not working, U1 pin 3 = 1V

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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