Wisar
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No red light but 4.9v power in...

Mon Jan 28, 2013 3:15 pm

...and only 1.7v showing on the GPIO 5v power (and only 1 on the 3v power). RPi has been working fine now gives me no lights at all. Power supplies are known good as they work for my other RPi. The one that is dead is my new 512mb model. Is there anything that I can do to conjur up a resurrection?

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rurwin
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Re: No red light but 4.9v power in...

Mon Jan 28, 2013 3:45 pm

Put it aside for 24 hours.

It sounds to me like the input fuse has blown. If you leave the board for an hour, and several hours just to be sure, it will recover.

Of course that assumes that you have found and removed whatever blew the fuse to start with. Was it in a box, or has it been damaged? Have you used any new peripherals recently? (it may take a long time for the fuse to decide to blow if there is only a small overload.) Was it sitting in direct sunlight or somewhere unusually warm?

Wisar
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Re: No red light but 4.9v power in...

Mon Jan 28, 2013 4:33 pm

Rurwin:

I was using a new power supply but it seems to be delivering ok power as measured and given that my other RPi seems happy with it...I was doing something new that in hind sight might not have been smart. The power supply is plugged into a switched powerstrip and I was using that to power cycle the RPi...it went dark shortly after a power cycle. Could that form of switching on and off send a spike of over voltage?

It has rested for 24 hours.........I assume that is resting as in unplugged......

Thanks,
Will

thsBavR10
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Re: No red light but 4.9v power in...

Mon Jan 28, 2013 5:27 pm

For powercycling you should use

Code: Select all

sudo reboot
or

Code: Select all

sudo shutdown -h now 
to avoid errors on SD card and file systems.

If you have a multimeter, please measure the voltage across the polyfuse F3.
For details have a look at http://elinux.org/index.php?title=R-Pi_ ... r_problems --> "How to test the F3 polyfuse".
Polyfuses recover from the tripped state to near their normal value in a few minutes, but do take some hours to fully recover so leave it unpowered and check it again in a little while.

Wisar
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Re: No red light but 4.9v power in...

Mon Jan 28, 2013 6:41 pm

I do try to do an O/S level cycle ...... assuming the RPi is alive and well! This is often not the case when mucking around with hardware configurations unfortunately. Is it bad to power cycle from a power strip?

I will do the power diagnosis of the polyfuse tomorrow morning when I don't have a beer in my hand.

Thanks for the input. This is one of the most responsive forums anywhere.

Cheers,
Wisar

thsBavR10
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Re: No red light but 4.9v power in...

Mon Jan 28, 2013 7:14 pm

Power cycling must not be bad, but i could damage the file system,
if something is written to open files when you cut the power.
Therefore it's better to cycle through commands, if it's possible ..

Wisar
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Re: No red light but 4.9v power in...

Tue Jan 29, 2013 8:07 am

Ain't those Polyfuses special???? After letting my RPi sit for 24 hours I plugged it back in and the red light flickered a little and then came on strong. IT LIVES AGAIN! I have another one on order thinking this one was KO so I am now going to be a three RPi family :-o.

Thanks for the above for the advice...
Cheers,
Will

Wisar
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 7:22 am

RPi is dead again :-(

This time there was a popping sound that can not have been good. The RPi was connected to a powered USB hub with a TV dongle inserted (and nothing else). There were also connections to a monitor and a network.

Post mortem examination of the two power supplies revealed that the 5v supply for the USB hub was completely dead. It also turns out that the power supply that I have been using with the RPi is delivering 5.4v which is above what the RPi would like to get. This doesn't explain the USB hub power supply going out unless there was a short circuit on the RPi through the USB bus??? I don't know it that makes sense or not. I have a feeling the RPi is going to be dead but I will try to do the power measurements mentioned earlier....

:-(

Wisar

P.S. I can not help but wonder if another couple of quid should have been added to the cost of the RPi to provide good power...and to protect against bad power. The circuit flashes the red power light if power is not good enough to run the Rpi. Would solve a WORLD of problems for users.

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rurwin
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 7:39 am

Wisar wrote: the 5v supply for the USB hub was completely dead. It also turns out that the power supply that I have been using with the RPi is delivering 5.4v which is above what the RPi would like to get. This doesn't explain the USB hub power supply going out
Yes it does. The USB power lines are connected directly to the incoming 5V. The USB power lines should not be connected to the USB power supply, but they often are. So the two power supplies were both trying to set the voltage level at different levels, like two people trying to fill the same bath to different levels. The Pi Supply had the tap full on, and the USB supply had the plug out and was bailing hard. That caused the input current to rise, and eventually caused the USB supply to die.

The good news is that, depending on how the USB supply died, there is a good chance that the Pi survived. But you should change that Pi supply to one with a more reasonable output.

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Lob0426
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 8:31 am

Hopefully your RasPi will live.

When you are trying a new USB powered hub:
Everyone should check their hubs for back-powering. A number of hubs have been seen to be non-compliant. Plug in your powered hub, then connect your Raspberry Pi. Do not power up your RasPi, plug the hub into one of the USB ports. If the RasPi's red light comes on, your hub is not USB compliant. If the red light does not show, you have a USB compliant hub.

There are three ways to deal with a non compliant hub. Modify the uplink cable to stop the back-powered condition. :? Modify the hub to stop the back-powered condition. :? Run your RasPi back-powered, if it will run stably that way. ;)

Well I guess there is a fourth, throw the piece of junk away! :shock: :lol:
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 8:36 am

you can't run the Pi backpowered like that if it's a rev. 1 with the usb Polyfuses.

Wisar
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 4:59 pm

The hubs that I have been using are 'def back powering the RPi. I was wondering why the power light was on with only the hub plugged in. How do you modify the hub to not backpower? I assume there are some, hopefully simple, electronics involved? How does one find out if a hub is compliant without spending money first?

Thanks, Wisar

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Lob0426
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 5:37 pm

You can cut the red wire in the USB uplink cable that came with your hub. Usually the easiest approach.

You can cut the power lead into the Uplink port on your hub. You can find a diagram of your particular connector type on the Internet.

You can see if it will run your RasPi all by itself. Just do not put power into the Raspberry Pi power connector. If it will run without resetting or corrupting your SD card then it is working. This is working for many people since the introduction of the board revisions. I have two running this way right now. Saves wires in your setup also, only one power supply, not two.

You really cannot find out if they are compliant before you buy them. I would like to see a list of the hubs being used and whether they are compliant or not. Maybe noted in the Wiki. Generally, so far, the non-compliant hubs have been the cheap USB hubs. Which is the ones we buy to use with the RasPi. :lol:

I actually want to find the models that are not compliant so I do not have to modify hubs, that are compliant. :twisted:
512MB version 2.0 as WordPress Server
Motorola Lapdock with Pi2B
Modded Rev 1.0 with pin headers at USB

http://rich1.dyndns.tv/
(RS)Allied ships old stock to reward its Customers for long wait!

Wisar
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Re: No red light but 4.9v power in...

Wed Jan 30, 2013 7:51 pm

Thanks Lob0426. One of my RPis is meant to be driving a little tracked 'bot and I am actually powering it from the hub in that instance. I blew this one up while messing around with some hardware on the test bench where I have been powering both the hub and Rpi separately. I think I read somewhere that you were not supposed to be able to power the RPi from the hub but I guess that might have been for version 1 incarnation per a post in this thread. I guess the trick will be to make sure that my chosen hub can deliver the power the RPi needs as it is extremely finicky!

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Lob0426
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Re: No red light but 4.9v power in...

Thu Jan 31, 2013 6:56 am

Wisar wrote:Thanks Lob0426. One of my RPis is meant to be driving a little tracked 'bot and I am actually powering it from the hub in that instance. I blew this one up while messing around with some hardware on the test bench where I have been powering both the hub and Rpi separately. I think I read somewhere that you were not supposed to be able to power the RPi from the hub but I guess that might have been for version 1 incarnation per a post in this thread. I guess the trick will be to make sure that my chosen hub can deliver the power the RPi needs as it is extremely finicky!
Yes; The version 1.0 boards need to be modded to work with back-power. You have to bridge at least one of the USB polyfuses. Rev 1.1 and later (ver 1.1's replaced the USB polyfuses with 0ohm resistors, version 2.0's have no polyfuses at USB) back-power just fine.

Suggestion for back-powering; use the shortest USB uplink (cable between RasPi and the USB hub) cable that you can find. I shorten my cables to about 5 inches (13cm). The shorter the cable is, the more voltage you are going to see at TP1/TP2. The 10 inch (25cm) cables seem to work well if you do not want to shorten one. The 2 foot cable that came with my hub read 4.5V at TP1/TP2. The 10 inch cable read 4.8V. The shortened cable (5 inches) read 4.92V.
512MB version 2.0 as WordPress Server
Motorola Lapdock with Pi2B
Modded Rev 1.0 with pin headers at USB

http://rich1.dyndns.tv/
(RS)Allied ships old stock to reward its Customers for long wait!

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