Pi3 shows yellow lightning bolt with official power supply

Yes, the yellow lightning bolt means "undervoltage". Normally "its right about it", i.e. when it says it's undervolting, that is usually the case.

The good news is that the pi itself will work just fine (and within spec) down to about 3.3V on the 5V input rails. The bad news is that HDMI devices that expect to be powered with 5V from the PI like the HDMI->VGA adapter that I have, will not be happy. Similarly, USB devices that are bus-powered will usually not like this situation.

As you have an HDMI screen (you see the yellow bolt), and don't need an HDMI->VGA adapter, and you can use a powered USB hub for USB devices that you need, the pi can still be tested.

But.... Before you go blaming the pi... I would recommend you test if the pi is "lying" or not. What is your 5V powersupply delivering? On the GPIO connector, nearest the corner, you find a pin with 5V (pin2). The pin along the edge of the PCB is another 5V pin (pin4). The next one is "GND". So get out a multimeter and measure it. Are you getting less than 4.75V ? Then the pi is right when complaining about low voltage level....

Thank you for your reply Roger. I did try a powered USB hub, but no connected devices would work.

But I'll power up my multimeter when I get home, and measure the 5V pins you suggested and post my findings here.

I tested pins 2 and 4 on the GPIO, and they both give 5.22volts when booted up (no USB devices connected). Any ideas?

Well... in that case, it seems that your pi is "lying" to you that the power is not sufficient. Just ignore the lightning bolt.

In practice I still find this such an odd "defect" to have, that I suspect that your powersupply is not coping enough with the sudden bursts of required power that the power dips below 4.65V very shortly, so that your multimeter cannot detect them.     

You say you bougth a powersupply specifically for the pi? Did you get the one from Element14 with the attached micro usb cable, or a different one?

The resistance of USB cables varies a LOT. I've done a measuring session, and the worst had a resistance of 6.5 Ohms, so at 0.5A (the pi3 can exceed that), you'd get a voltage drop of 3.25V, start out with 5.25 and there will be only 2V left, too little to run a pi. But even a 1 Ohm cable will not cope well with the spikes possibly triggering exactly what you are seeing.....

I can not ignore it, because none of the USB devices I connect work. The same setup works fine on my Pi Zero.

Here is the power supply I am using, with a fixed cable: https://www.kiwi-electronics.nl/raspberry-pi/raspberry-pi-stroomvoorzieningen/rpi-psu-5-1v-2-5a--eu-uk

I agree, Roger.

I have seen several 'official' Raspberry Pi PSUs that are not from raspberrypi.org. The genuine items have the official Raspberry logo on the case and have a 'bell-wire', figure-of-eight, captive cable.

I have used any one of three genuine official PSUs with the 'bell-wire' connection rather than USB cable and they run a 15.6" USB powered HDMI monitor, a wireless keyboard dongle and a USB powered audio interface that drives two condenser microphones with 48V phantom power. This is only possible with the Pi3.

There is a brief low-voltage indication on boot and when the audio interface is plugged in. It quickly fades away once the devices are fully connected. You would have to put a very high USB load on the system to get anything but brief power warnings.

All of the above is driven solely by the Pi PSU. It is also possible to run the above from a mobile phone, mobile battery charger, but only with 10cm USB cables.

I doubt that a digital multimeter would catch one of the brief brownouts. A good analogue meter with a pointer is more likely to show the extent of the power loss.

Well, if you click my link you see the PSU does have the official logo on it. A friend of mine who is a lot more technical than I am is checking the unit and noticed the green activity led doesn't turn on. But the led is not broken (he tested that too!).

Elmar,

That looks just like my two black ones.

Your green LED should at least flash during the boot phase.

It doesn't flash during boot either.

I wonder if increasing the Over_voltage= setting in the Raspberry Pi 3 Config file would have the effect of increasing the voltage available to these chips, therefor getting rid of the lightning bolt.

I would be very interested to know the relationship between overclock, lightning bolt, and the over_voltage setting.

On a Overclocked Pi, could I keep increasing the over_voltage setting until it disappears?  Or is something fundamentally wrong with my overclock?

Official 2.5A canakit powersupply on a pi3 running conservative Overclock settings in a Nespi Case:

total_mem=1024
arm_freq=1320
gpu_freq=510
core_freq=510
sdram_freq=500
sdram_schmoo=0x02000020
over_voltage_sdram_p=6
over_voltage_sdram_i=4
over_voltage_sdram_c=4
over_voltage=3
sdram_over_voltage=2
avoid_pwm_pll=1
v3d_freq=510