Nicky25
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Low Voltage Rainbow

Sun Jul 24, 2016 8:31 pm

Hi, new to the forum.

I am currently using the RPi 2, problem is that the low voltage rainbow is being displayed. When measuring the voltage at the GPIO the 5v pins are at 5.35v and the 3.3v pin is at 3.348v. It has been going on for a month or so and has spent a week or 2 not powered on. The power supply is connect to the Mains and can output about 2A. I haven't witnessed any resets or it freezing.

Any advice or should I just not worry about it?

Regards,

Nicky

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davidcoton
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Re: Low Voltage Rainbow

Sun Jul 24, 2016 9:55 pm

Hmm. Very strange, the warning should only appear when the voltage is below 4.65V. Is the red power LED on?

Are you sure of the calibration of your meter?

See Dom's post here -- this command will show if the CPU has been throttled, and why. Low voltage is one cause, so if the voltage is being read as low, this command will show it.
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Nicky25
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Re: Low Voltage Rainbow

Mon Jul 25, 2016 5:48 am

Hi, Thanks for your reply.

The output from that is:

Code: Select all

throttled=0x50005
Couldn't really understand how the post that you suggested decoded them, but it is the same one in the example which means there is undervoltage and throttling.

The DMM is okay as I have measured other power supplies and they all came up with the appropriate voltage. The red Led is also on.

Regards,

Nicky

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RaTTuS
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Re: Low Voltage Rainbow

Mon Jul 25, 2016 7:24 am

I suggest that your meter needs a new battery and/or calibration.
5.35V is far too much for a RPI

that output means you are under voltage [and the flashing rainbow means the same]
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Nicky25
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Re: Low Voltage Rainbow

Mon Jul 25, 2016 8:58 am

Thanks for your reply. So I connect the RPi 2 to a battery pack. The 5v at the gpio is now 5.07v and the 3.3v rail is at 3.349v. The command

Code: Select all

vcgencmd get_throttled
is still showing

Code: Select all

throttled=0x50005
The rainbow icon is still there and is not flashing.

My DMM is not showing a low battery although if you say that it could be the battery of the DMM then I will change it.

Any ideas?

Regards,

Nicky

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RaTTuS
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Re: Low Voltage Rainbow

Mon Jul 25, 2016 9:13 am

try another micro USB lead
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Nicky25
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Re: Low Voltage Rainbow

Mon Jul 25, 2016 9:19 am

I am trying a different USB lead. 5v rail is at 5.02v and the 3.3v rail is at 3.349. The rainbow icon is still being displayed.

Both USB cables used can handle 2A. The battery bank also has no problem giving out 2A.

Regards,

Nicholas

Nicky25
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Re: Low Voltage Rainbow

Mon Jul 25, 2016 9:27 am

Could the problem now be the poly fuse? I am going to leave it a couple of hours off.

Regards,

Nicky

Nicky25
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Re: Low Voltage Rainbow

Tue Jul 26, 2016 12:14 am

Just an update on the poly fuse theory. The RPi has been unplugged for a few hours and nothing has changed. It was plugged into the battery bank.

Regards,

Nicky

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Burngate
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Re: Low Voltage Rainbow

Tue Jul 26, 2016 8:53 am

The poly-fuse is between the u-usb power input and the rest of the circuitry, including the GPIO header and the low-voltage detection circuit.
So a measurement of ~5v on the header means the poly-fuse is not the cause of your problem.

The red power LED is attached to the low-voltage detection circuit, and in parallel there is a connection to GPIO 35 to inform the SoC of the condition.
If the red power LED is on, but the arm is being informed of a low-voltage condition, there is a disconnect between the output of the low-voltage detection circuit and the arm.

It could be the track to the SoC, or the software in the SoC, but my guess would be a faulty GPIO 35.
How it got damaged is unknown, but fixing it is easy - buy a new Pi.

Nicky25
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Re: Low Voltage Rainbow

Tue Jul 26, 2016 9:33 am

Hi, thanks for your helpful reply.

So this means that there is practically no harm being done and can continue to run normally? I saw that you can set an ignore_warnings parameter in the setup file thing, would this solve this problem?

Regards,

Nicky

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