F1/F2 polyfuses gone

For those of you wanting the executive overview:

jbeale wrote:I just received my 2nd R-Pi, this one from stock (yay MCM Electronics) which took just a week to ship from Ohio to California. I was pleased, but surprised to see that the USB fuses F1, F2 are now just 0-ohm jumpers (photo below). I was able to confirm they measure less than 0.1 ohms. Is this the new standard going forward?

by Burngate

You've obviously recieved a Chinese pirate copy - it won't have all the features a proper Pi would have, such as not working with some keyboards, and the like.

by eben » 25 Aug 2012 10:34

Yes. After seeing how many people have decided to modify their boards with zero-ohm links, and having done some safety and reliability testing, we've decided that the best course of action is to remove the USB fuses from the design. Right now they're linked out, but on a subsequent board revision the pads will be removed entirely.

by liz » 25 Aug 2012 10:37

And I'm impressed someone noticed so quickly!

From Me Peg: Unlike on this Forum, I do not read every little thing on the org forum. . . BUT . . . is it just me or does this seem kind of sneaky? Or to put it another way. . . what happened to the "Open" in the open software/hardware world? Or did I miss the instructions on what to do with the two pi's I now own to make them more stable? No suggestions on buying the beagleboard Morgaine!

For those of you wanting the executive overview:

jbeale wrote:I just received my 2nd R-Pi, this one from stock (yay MCM Electronics) which took just a week to ship from Ohio to California. I was pleased, but surprised to see that the USB fuses F1, F2 are now just 0-ohm jumpers (photo below). I was able to confirm they measure less than 0.1 ohms. Is this the new standard going forward?

by Burngate

You've obviously recieved a Chinese pirate copy - it won't have all the features a proper Pi would have, such as not working with some keyboards, and the like.

by eben » 25 Aug 2012 10:34

Yes. After seeing how many people have decided to modify their boards with zero-ohm links, and having done some safety and reliability testing, we've decided that the best course of action is to remove the USB fuses from the design. Right now they're linked out, but on a subsequent board revision the pads will be removed entirely.

by liz » 25 Aug 2012 10:37

And I'm impressed someone noticed so quickly!

From Me Peg: Unlike on this Forum, I do not read every little thing on the org forum. . . BUT . . . is it just me or does this seem kind of sneaky? Or to put it another way. . . what happened to the "Open" in the open software/hardware world? Or did I miss the instructions on what to do with the two pi's I now own to make them more stable? No suggestions on buying the beagleboard Morgaine!

> is it just me or does this seem kind of sneaky?

Also makes you wonder what other unannounced changes

have been made.  I notice that there haven't been any reports

recently of X1 crystal problems requiring refrigeration, or any

damaged TV's, so perhaps there have been some part substitutions

there too.

The last words out of user lostintime's mouth before he was banned

yesterday turned out to be quite prophetic:

   "I find it unacceptable that the Raspberry Pi Foundation has yet to formally acknowledge that the Raspberry Pi has any problems whatsoever, meaning it's quite easy for people to purchase a Pi while being completely oblivious to the fact that it has a known issue in a critical area which will affect the majority of its users in some way and which may never be fixed. It will be interesting to see what changes are made to the Raspberry Pi's hardware in the future and how they are justified by the Foundation when this situation is considered."

Peg Wagner wrote:

 

by liz » 25 Aug 2012 10:37

And I'm impressed someone noticed so quickly!

 

From Me Peg: ... is it just me or does this seem kind of sneaky?

In the F1/F2 case, perhaps RasPeople didn't announce the change because they didn't want 10,000 cranky customers complaining that they want the Ohmless version, adding to distributors' confusion.

So for their next trick, perhaps RasPeople will modify the 1V8 connection to separate out the LAN9512 and its caps -- and they won't tell anyone about that one either.  The 1V8 change will be really hard to notice. 

Thanks for the heads up on the 0-ohm change.  Someone at my hackerspace Pi meetup last night told me he got his Pi from MCM last week, so I asked I could see it... and it was indeed "ohmless":

I'm very interested to see at a future meeting what will happen when we swap his Pi into someone's setup who is having trouble with USB devices that might be power related.  With the USB host port polyfuses gone, I'm wondering if it is still be necessary to recommend using a self-powered hub for a WiFi adapter.  (the GWU625 I've been using lists "Transmit : < 380mA. ; Receive: < 250mA").

I was tempted to replace the fuses by a pair of 0 ohm resistors but I only had 1206 size and didn't like how they landed on the pads,

casually I had some 500mA polyfuses of the same size, so I used those.

After the change I didn't have any problems to have an old Digitus Dongle with the Realtek 8187 chipset working directly from the

one of the R-Pi USB ports, this dongle says on the ConfiguratorDescriptor.MaxPower: 500mA

Ddin't do much to test if there is any packet loss issues with WiFi.

-J

For the polyfuse on the micro usb power input, I see on the eLinux wiki it is 1.1A with a hold current of 700mA.  Does that mean the Pi can only draw 700mA before the polyfuse starts to gain resistance and decrease the 5V input? 

I'm guessing the downside to 0-ohm or bigger 500mA polyfuse is that the USB devices can now draw enough current to make the power input polyfuse react.  I wonder if this would effect the functioning off the rest of the Pi (which I think it using 3.3V and 1.8V rails, right?).  Hookup an external harddisk directly and the Pi reboots?

> Hookup an external harddisk directly and the Pi reboots?

We don't really know what the future plans are for power distribution. Morgaine has advocated that the USB power shouldn't go through F3. Some people have suggested 1 ohm instead of zero, or larger capacitors, in order to prevent voltage sags from hot plugged USB devices. Anyway, this change seems like an improvement, even if it doesn't solve all the power issues.

I can't really say, forgot to mention that I'm actually powering the R-Pi from the P1 header so I'm totally bypassing the main fuse.

-J

I can't remember if there is an specific value required/recommended by the USB 2.0 standard, I've been usnig 150µF and the reference design schematics and eval board for the SMSC LAN9512 show that value as well for each port.

The R-Pi has a single 47µF shared by both ports.

PS. I"m still waiting to see what else is on "Pete's list", this "silent" fix by RPF replacing the polyfuses by a 0 ohm resistor is another engineering oddity and it does not sound professional that they decided to do it (and apparently testing it) because we were doing it, they should have a more reasonable explanation.

-J

ah, good point, I forgot about powering via P1.

I just love it how the fanboys on the original forum praise the modification that makes their Pi even the more perfect design.

Using one capacitor for both usb ports (but with a sufficient value) shouldn't work much different than using a capacitor for each port. It will have a bit higher ESR, but it's not there to continuously flatten ripple voltages.

A bigger capacitor is a more expensive component, and we all know how hard it is to keep the low price for the board.

The camera and dsi connector make me wonder if education is really the goal of the foundition, or if that is just a fog screen to rectify the 'non profit' nature of the foundation? They missed the start of the 2012 - 2013 schoolyear. Their low price setting is great, but for a workable classroom setup, you need to add the price of a monitor, a keyboard, a mouse, a hub and a housing. The board on it's own is just part of the setup. So the only benefit compared to a netbook or cheap tablet is the fact that students can go back to basics, except, that such requires an open approach upon hardware an software? Maybe they can learn how to do reverse engineering of the binary blob. It will give them great job opportunities later on in chinese cloning factories. Altough I hope no one tries to clone the synoptics otg usb stack.