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No post, no boot

Former Member

Just got my Rasp PI 3's and went to set them up last weekend and get no post

no boot.  I am using a 5v 1A standard cell phone charger.  The same one that

powers my first gen PI.  Can somebody shed some light on this or should I request

an RMA.  I bought 2 of them and neither one would boot.  not a flicker...Oh a red

light came on, but that is it.  Any suggestions....

 

Thanks

Parents

  • You need to use the 'Official' 5.1 V PSU.

     

    Please read the following threads to find out why.

     

    https://www.element14.com/community/message/178336/l/re-rpi-3-nousb#178336

     

    https://www.element14.com/community/community/raspberry-pi/blog/2014/03/07/raspberry-pi-usb-power-cables-crashing-and-other-problems

     

    The current output of a PSU at 5 Volts makes no difference. The problem is that USB cables, even those claiming to be 'charger' cables, have too much resistance. 5 Volts at the PSU drops to 4 Volts or less at the Pi when connected via the typical 1.8m USB cable.

     

    The official PSU has a long lead, but it is low resistance due to its heavy 18 AWG wiring. Most USB cables are a much smaller 28 AWG (the wire gauge is often marked on the cable). The PSU also produces 5.1 Volts rather than 5 and this is sufficient to ensure a Pi 3 receives sufficient voltage even when running at its specified maximum current (e.g. with all the USB ports connected to devices that demand high currents).

     

    The only alternative to the official power supply is to use any competent 5v PSU that can supply the total current you need together with a very short USB cable. It must be no more than a quarter of a metre long (250cm) and preferably less. My Pi 2B will not run on a 5 Volt PSU and a half metre lead, even with just wifi and wireless keyboard and mouse combo plugged in.

  • in reply to royleith

    To clarify a few things.

    1. You don't "need" the official PI power brick but for the price, if your need to get one, it is a very good deal and your can't really go wrong with it. The basic RPI3 does not take much more power than the PI2 and in no way requires the power of the new adapter. the rating of this adapter is to cover the additional power support for the USB ports. A good USB adapter that really does give out 5V at an amp or two will work just fine but as you already know (I saw you linked in an old article of mine re crashing PI and USB cables), you must use a good USB cable to go with it. If you see the small rainbow square appear in the top right corner even for a few moments only then your running close to trouble

     

    If you suspect the power to the PI, then boot with ONLY the Monitor, SD card and Power lead attached, if it boots and shows no signs of the rainbow then add more devices. BTW, this is not the BIG rainbow that appears as soon as you power on, it is a small one in the top of the screen.

     

    NEVER assume someone has loaded the SD card correctly for you and tried it. If a teacher has specifically told you they have and tested it too, then there of course is some level of confidence, but if they just did a bunch for a whole class then stuff happens and mistakes ensue. Be prepared to re do it our self.

     

    YES you can just do a drag and drop to a properly formatted SD card using a windows machine, but I emphasise "Properly formatted"

    See my videos here to get you started, I have loads more on my channel

     

    If you're not using the Official PI LCD display and are connecting through HDMI then there really is virtually nothing that can go wrong if you follow these instructions.

    Hope it helps

  • in reply to Robert Peter Oakes

    I fired up my RPi3 using the old Samsung charger and it went just fine ...

     

    As Peter said if you add lots of USB, wireless and other accessories, then you'll need the extra current capability.

     

    Most phone chargers are designed to charge a 3.7v Lithium battery, not provide a nice 5v supply.

     

     

    Mark

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