VIN 36V when it’s actually 12V
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Hi,
I suspect that I’ve got a short somewhere on my Duet 2 WiFi. On the browser interface it says my VIN is 36V which is impossible because my power supply can only deliver 12V. I checked my fuses and saw that my fan fuse was blown. I replaced it, but there was no change in the VIN value. It also says that my cpu or what it’s called, is 50C right after boot up. That’s strange right? It doesn’t feel like 50C.
I think I’ve blown something on this board, but I don’t know which component. Does anybody have any suggestions which component i should check?
Thank you for reading this.
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Prime suspects would be the cpu itself, (biggest chip) or possibly the voltage divider R15/R16. Probably easier to just get a clear picture and upload here.
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No obvious damage to be seen, the voltage divider was a bit tricky to read off the pictures, but the other one R80/R81 has the right values so odds are both are correct. That leaves the CPU, probably something you'd want to contact your vendor about if the board is still under warranty.
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VIN is measured by feeding it through a voltage divider into an ADC input. So either the ADC in the microcontroller is faulty, or the ADC reference voltage (ADCVREF) is much lower than the intended 3.3V. You can measure ADCVREF, it's pin 41 on the expansion connector.
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Can you measure the voltage across R81 too?
Are your thermistors reading correctly?
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@wennis said in VIN 36V when it’s actually 12V:
Voltage on R81 is 3.26V
That's much too high! Almost as if it's shorted to +3.3V or VREF.
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Oh I see... does it mean the resistor is faulty and I should replace it?
Do you know which replacement part I should get if that’s the case?
Thank you for your help!
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SMD resistors rarely fail. The only time I have seen one fail, under magnification I could see a crack in it.
I suggest you use your multimeter to check its resistance.
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R81 was around 60 ohms. Is that okay?
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looking here, R81 should be 4k7
https://github.com/T3P3/Duet/blob/master/Duet2/Duet2v1.04/Duet2_1.04b_Schematic.pdf -
I suspect a short or near-short between that ADC input and +3.3V. It could be caused by a blown pin in the microcontroller, or by a bit of metal swarf shorting two pins of the microcontroller together.
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Okay, that doesn’t sound good. Are we talking about the U3 chip or the ARM chip?
I tried to clean the connection on the U3 chip, but it made no difference.
I’ll just get right to it. Is my board a dead board?