I have a pi model B being used to read from a rfid card reader.

After a week or so of continuous use, it powers down and the red light goes dim; enter image description here

If I check the voltage across TP1 and TP2, I get 2.615 volts;

enter image description here

However if I measure the voltage across the supply its giving over 5 volts; enter image description here

If I power cycle, it comes back up, and the TP1-TP2 measures 5 volts again.

  • 1
    The only thing that comes to mind is the 3.3v regulator goes awol and for some reason doesn't operate properly. The BCM is powered by 3.3v and the LED's so thats why it does that. How to fix.. supply your own 3.3v but it must be regulated and filtered.
    – Piotr Kula
    Dec 2, 2014 at 22:05
  • how would I test that?
    – Tom
    Dec 3, 2014 at 7:21
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    You will need the schematics for your version. Found at the official Pi website. Identify the 3.3v compononent on the PCB, look at the white text on the component, search for that specific specification and pinout. Then read what functions it has and what pins they are, test them. Do not rely that each Pi uses the exact same components. There are equivalents that can be used with different "features" or better cost varying from time to time so they might be different.
    – Piotr Kula
    Dec 3, 2014 at 9:08
  • Any luck with this? :)
    – Piotr Kula
    Feb 21, 2015 at 1:22
  • 1
    I replaced the pi with another model B, and that one isn't doing the same thing. The problems with the original one became more frequent, so I suspect it was hardware problems as a result of overloading it or using substandard PSU. This new one has the +v for the rfid reader on a separate +5V
    – Tom
    Feb 21, 2015 at 5:03

1 Answer 1


Over time this problem became more frequent, under similar load and environment, so I suspect it was a hardware issue. I replaced the pi with a new one, and I don't get the same behaviour. I have since moved the rfid reader to use a separate +5V PSU so ease load directly on the rpi +5v rail. This seems to help.

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