You have a Raspberry Pi, everyone is connected, ready to go… but when you plug in the power, nothing happens. Something, somewhere is wrong, but what? And what can you do about it?
Here are five things to check if you need to troubleshoot a Raspberry Pi that should work but won’t boot for some reason.
1. Make sure it’s not a download, check the LEDs
When the Raspberry Pi boots up, one or more LEDs will turn on. One red, indicating power (PWR); the other is green and indicates activity (ACT). (There are also three LEDs showing Ethernet status, if connected.)
So what do these LEDs mean? Well, there is a normal condition where both PWR and ACT lights are on. ACT will flash when the SD card is active, and PWR will flash when the power drops below 4.65V. Thus, if the red PWR LED does not light up, there is no power.
If only the red PWR LED is active and there is no blinking light, then the Pi is receiving power, but there is no readable boot instruction on the SD card (if present). On the Raspberry Pi 2, the ACT and PWR LEDs are lit, which means the same thing.
When booting from an SD card, the ACT light should blink irregularly. However, it may flash in a more controlled manner to indicate a problem:
- 3 flashes: start.elf not found
- 4 flashes: start.elf cannot start, so it may be corrupted. In addition, the card is not inserted correctly or the card slot is not working.
- 7 flashes: kernel.img not found
- 8 flashes: SDRAM not recognized. In this case, your SDRAM is probably corrupted or the bootcode.bin orstart.elf file cannot be read.
2. Is the power adapter good enough?
As noted above, power issues can cause your Raspberry Pi to crash. It may shut down or freeze while running, or it may not boot at all. This is because a stable power supply unit (PSU) is needed to reliably read an SD card.
To make sure your power supply is good enough, make sure it matches the specification for your specific Raspberry Pi model. Similarly, make sure the micro USB from the power supply to the Pi is down to zero. Many people use smartphone chargers to power their Raspberry Pis. This is usually not the best idea; a dedicated, suitable power supply is the preferred approach.
The Raspberry Pi has a resettable fuse. This polyfusus may clear itself, but it may take up to a few days. If you accidentally start polyfuse, you will only know about it the next time you try to boot. It’s worth taking the time to buy a suitable Raspberry Pi power supply, such as the CanaKit 5V 2.5A adapter at Amazon.
3. Is the operating system installed?
So, if there is no OS installed on the SD card, you will not enjoy the Raspberry Pi. Do this by making the OS available. Install Raspbian (or Raspbian Lite if you’re short on time) or use NOOBS to start your Pi and select an OS to download and install.
4. Make sure the MicroSD Card is working
A working Raspberry Pi will rely on a good quality SD card to boot and is usually running an OS (although later models may subsequently boot from USB devices). If the SD card is not working then your Raspberry Pi will be unstable or simply won’t be able to boot.
Let’s start by checking the health of the card. You can do this by turning off your Pi and inserting an SD card into your computer. Use a trusted flash drive formatter and try reformatting (on Windows and Mac, use the SDFormatter tool from the SD Association). If the format fails, the card is damaged (SD cards from SanDisk can be returned under warranty).