It works!

Yay, I received my Pi at last!

Following John's good precedent, I measured my polyfuse resistances to be:

F1 = 4.0 ohms

F2 = 3.2 ohms

F3 = 0.3 ohms (but maybe close to 0.2, occasional flicker), LS digit questionable

These values are a lot higher than John's.  I used two different DVMs, one of them a costly Fluke (although not calibrated), but neither has probe lead resistance nulling (I subtracted the 0.2 and 0.3 ohms indicated when the probes are shorted).

Allowing for the lead offsets, the two DVMs track each other perfectly across this range, so I have confidence in the results.  I don't regard the F3 reading as reliable, since it's on the least significant digit displayed.  It's too high for comfort though (0.5 and 0.6 ohm readings on the DVMs) --- in effect the board's +5V is unregulated because of it.

F1 and F2 are outrageously high of course, and do more harm than good by deregulating the supply even further.  This is a plain and simple design fault.  Also, the fact that F1 and F2 have so greatly differing resistances is a worry --- clearly this component does not have a tightly defined resistance parameter, even worse when compared with John's.

I haven't powered the board up yet, as I must be the only person on the planet without a micro-USB charger.

I'll pop out and buy one today, or an adapter for a barrel connector or something.

Morgaine.

Followup to measuring the polyfuses and shopping for a few means of applying power to the Pi ...

Short version:  everything worked first time, but the Pi is piping hot! 

Longer version:  Maplins came up trumps with lots of options for micro-USB power.  This one ---http://www.maplin.co.uk/micro-usb-power-supply-393067  --- even says "Can be used with the Raspberry Pi system" on the product page, lol.  Everyone is getting in on the Pi bandwagon.

That 1A power supply (which does seem to deserve the name, rather than merely "charger") supplies my Pi with 5.01V at the input to polyfuse F3, and I see 4.89V at TP1, when running a basic system load comprised of a Logitech universal receiver which runs totally cold, Ethernet, and HDMI into the HDMI input on a Dell 2408 monitor at 1920x1200.

Pulling out the Ethernet cable raised TP1 by 30mV without any significant change at the input.to F3, so this supply is regulating and its lead seems to be very good.  Pulling out the Logitech receiver raises TP1 by only 10mV.  Pulling out the HDMI lead has no effect on TP1.  My peripherals are taking very little current.

Under these condition, the finger test applied to the SoC/PoP (which BTW is a Samsung) has to be removed in under 10 seconds to avoid pain.  Applied to the LAN chip, the finger has to be removed almost instantly --- this device is running very hot indeed, both with and without the LAN cable.

Nothing else to report really.  I don't know Debian specifically but experience from many other distros made everything easy.  The nearest thing to a hiccup was that "apt-get install gpm" failed to configure the mouse, so I had to modify /etc/gpm.conf slightly before it would work (changed the mouse device to /dev/input/mice).

As an aside, I also bought http://www.maplin.co.uk/high-power-usb-charger-with-travel-adaptors-513509 on the expectation that its 2.1 A rating would quite likely offer better regulation, but that's not what I observed:  it delivers 4.75V at TP1 under the same load described above.  The blame might lie with the lead rather than the charger (haven't checked yet), but that's not what appearances would suggest as the lead is nearly twice as thick as the one on the better supply.  Of course, the extra thickness could be all plastic.

So, a successful start with my Pi, but running the LAN9512 that hot is a bit worrying.

Morgaine.

Morgaine Dinova wrote:

 

Under these condition, the finger test applied to the SoC/PoP (which BTW is a Samsung) has to be removed in under 10 seconds to avoid pain.  Applied to the LAN chip, the finger has to be removed almost instantly --- this device is running very hot indeed, both with and without the LAN cable.

 

So, a successful start with my Pi, but running the LAN9512 that hot is a bit worrying.

 

Morgaine.

Thank you for the write-up.  It's interesting that the RasPi forum doesn't seem to have a place to write up success, only problems :-)

It would be interesting to find out the LAN9512 temperature range seen in the field.  Some people have reported blazing hot as you have, others something more reasonable.  My fear regarding the LAN9512 is that its thermal performance may depend heavily on how well its large ground pad is soldered, which is impossible to see without an X-ray (if then).  How hot is the back side of your board?  When I first picked up my RasPi after running her the first time, the back side (which was sitting on the anti-static bag) was very hot. That's when I decided to get out some tools and make my vertical mount frame.  Radiating from both sides keeps her very comfy.

My Pi was one of the first released batch and my LAN chip gets warm but not hot, which makes me wonder if there has been any component changes or if some manufacturing defect such as partial shorts or poor soldering have it the later batches.

There have been some apparently minor differences in the markings on

the LAN chip, but nothing correlated with temperature. 

The thread "Ethernet chip gets raging hot" started on May 15,

http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=5898

so this isn't a particularly recent issue.

As far as I know, the only official comment was from Gert in the

above thread, who wrote:

"It might be warm, it should never be hot."

and later wrote:

"I can imagine that you do not want to give up your Pi now. But when a few more are available I would really send it back so somebody can find out why it gets so hot."

So maybe you will be the first person to take them up on

this offer, now that we know replacements are readily

available.  They really ought to publish what they consider

to be the normal temperature range, as well as what they

consider to be the normal range for polyfuse resistance.

Measuring the current into your 'pi is a bit more difficult than, measuring the voltage across TP1,TP2.

But I'm guessing you're seeing the same as me, judging from the voltages you measure across F3. We're using the "has too much resistance" fuse as a current sense resistor!

My 'pi has 140mV across F3. Yours has only 120mv. Either your polyfuse is a bit better, or your 'pi is using slightly less power. But in the grand scheme of things: Your pi is using the same amount of power as mine.

All power used gets converted into heat. Your pi is not producing more heat than mine.

The only think I can think of that would make the lan9512 hotter than it should be is if your 3.3V is WAY too high. We measured 3.31V on ours the other day. Measure it, the tab is 3.3V, TP2 is GND.

On the other hand, that would increase total power usage....

The thermal resistance between where the power is generated and the outside of  the package is much less for the lan than for the soc. That might lead to a percieved temperature difference.

Put your finger on the chip, when it becomes uncomfortable, swtich fingers. I'm guessing that the second or third finger won't have any trouble staying on the chip. Your finger is now acting as a heatsink. At first the thermal capacity of the package was heating the finger beyond "comfortable", but after getting rid of that heat, if your finger is able to dissipate the heat, it's less than 1W.

Or at least, with my fingers its less than 1W. That's what I measured once.

The power on the 'pi shares between the 3.3V regulator, the soc and the lan chip. And input power is about 2.4W, so at most 1W for the lan and soc and a little less for the 3.3V.

Measuring the current into your 'pi is a bit more difficult than, measuring the voltage across TP1,TP2.

But I'm guessing you're seeing the same as me, judging from the voltages you measure across F3. We're using the "has too much resistance" fuse as a current sense resistor!

My 'pi has 140mV across F3. Yours has only 120mv. Either your polyfuse is a bit better, or your 'pi is using slightly less power. But in the grand scheme of things: Your pi is using the same amount of power as mine.

All power used gets converted into heat. Your pi is not producing more heat than mine.

The only think I can think of that would make the lan9512 hotter than it should be is if your 3.3V is WAY too high. We measured 3.31V on ours the other day. Measure it, the tab is 3.3V, TP2 is GND.

On the other hand, that would increase total power usage....

The thermal resistance between where the power is generated and the outside of  the package is much less for the lan than for the soc. That might lead to a percieved temperature difference.

Put your finger on the chip, when it becomes uncomfortable, swtich fingers. I'm guessing that the second or third finger won't have any trouble staying on the chip. Your finger is now acting as a heatsink. At first the thermal capacity of the package was heating the finger beyond "comfortable", but after getting rid of that heat, if your finger is able to dissipate the heat, it's less than 1W.

Or at least, with my fingers its less than 1W. That's what I measured once.

The power on the 'pi shares between the 3.3V regulator, the soc and the lan chip. And input power is about 2.4W, so at most 1W for the lan and soc and a little less for the 3.3V.