totoharibo
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Re: Wifi dongle not working

Tue May 28, 2013 1:56 pm

don't plug the Wifi dongle while working.
plug it in before powering up

At the same time verify youyr power pack Io > 1A

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redhawk
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Re: Wifi dongle not working

Tue May 28, 2013 2:39 pm

Is your Pi the original board with the polyfused USB ports??

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btidey
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Re: Wifi dongle not working

Tue May 28, 2013 2:47 pm

Check your power usb cable while your at it. The combination of the main polyfuse resistance and a spotty cable can easily add up to 1 ohm of round trip resistance and then it doesn't matter how good the power supply is.

A short dedicated charging cable is probably the best bet.

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redhawk
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Re: Wifi dongle not working

Tue May 28, 2013 6:57 pm

Near the LED indicators there should be the label F1 and F2, do you see green slabs or black ones or neither??

(like in this photo)
Image

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btidey
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Re: Wifi dongle not working

Tue May 28, 2013 7:39 pm

That means you have a v2 board and there is no limiting fuses on the USB +5V supplies which did cause problems with earlier versions. So that's good, but doesn't solve your problem.

Do you have access to a multimeter? If so then measure the voltage between TP1 and TP2 on the board. It should be between 4.75 and 5.25. This is the best check that power is not the problem. You could maybe check it with the wifi in and out.

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mahjongg
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Re: Wifi dongle not working

Sat Jun 01, 2013 6:12 pm

Its not a question of "safe", but with 4.69V its no wonder your USB dongle isn't working. And even 4.80 V is marginal, just 0.05V over the minimum of 4.75V. Either your PSU is insufficient, you micro-USB cable is too long and/or thin, of your polyfuse has been triggered, and has not recovered still.

A passive (unpowered) hub makes things worse, not better, it will introduce more power loss, not solve it!

You need a hub with its own power supply!

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mahjongg
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Re: Wifi dongle not working

Sun Jun 02, 2013 1:12 am

check (measure) why you have a lower voltage than you should have, is it already low directly at the PSU or is there a loss somewhere along the way. Perhaps in a bad cable, or in the polyfuse. use logic and reasoning.

a powered hub uses its own power to power the USB devices its powered, a passive hub draws all the power, it and the attached devices use from its host.

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pluggy
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Re: Wifi dongle not working

Sun Jun 02, 2013 8:59 am

On the back of the board, with it powered up, measure the voltage across the component (the polyfuse) marked F3 next to the micro USB socket. Or between TP2 (Gnd) and both sides of the Polyfuse. If the voltage drop or difference between the 2 readings is much more than 0.1 Volts, its the polyfuse.
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pluggy
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Re: Wifi dongle not working

Wed Jun 05, 2013 6:58 pm

Image

http://www.pluggy.me.uk/raspberry/probepoints.jpg

Meter set to Volts and something greater than 5 (usually 20V).

Black probe on point circled in black

Red probe on Red 1 - Take reading

Red probe on Red 2 (or 3) - Take reading

Put the two readings on here

Red 3 is the back of TP1 and Black is the back of TP2.

Red 3 should give the same reading as Red 2

Theres a video here for the voltage across the standard TP1 and TP2

http://www.youtube.com/watch?v=W3nH-Bh1Q0Q

Except he puts the probes on the wrong way round and his meter is reading minus 5.00 V

Theres the official version here : http://elinux.org/R-Pi_Troubleshooting# ... r_problems

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pluggy
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Re: Wifi dongle not working

Thu Jun 06, 2013 3:00 pm

Your polyfuse is OK, the power supply voltage / is a bit on the low side or the cable between the power supply is causing a voltage drop. 4.7V puts it in the shady area for voltage, maybe OK, maybe not. I've had no problems at less than that, but its outside the 5% margin (4.75 V) and the widely accepted 4.8 'safe' voltage.
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k6mle
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Re: Wifi dongle not working

Thu Jun 06, 2013 6:11 pm

I use a power supply intended for the Kindle Fire (5V @ 1.8 A), which works very well with the RPi. It might be a current draw issue that's causing your voltage drop, i.e. you're pulling current at or near the maximum that your power supply can deliver. You typically want a supply capable of delivering roughly 30% more than required, just so there's adequate overhead.

Gustavo_Murta
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Re: Wifi dongle not working

Fri Jul 26, 2013 3:41 pm

Anon,

In my opinion the voltage must be closest to 5,0Vdc. I think if you are measuring 4,8 V, it is not good enough,
Use good power supply. ( 5V >= 1A ) . I made mine power supply using 7805 regulator an I measure 4,95V !
And use USB Hub with additional external supply .

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