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.

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.

@coder27: "Raging hot" describes the temperature of my LAN9512 perfectly too, so if Gert says that it should not be so, it's faulty.

@Roger: I did your suggested finger-switching to drain the thermal capacity of the chip surface, and you're right, it has only a small thermal reservoir.  Using up to 4 fingers in sequence, the 1st has to be removed as fast as human reactions allow (it's not charring, but seriously beyond cell survival temperature), the 2nd maybe 1/5th second, the 3rd a whole second, and the 4th up to 5 seconds.  I can't extend "Finger Contact Survival Time" any longer than 5 seconds no matter how many times I switch, I'm not into pain.

In the absence of a thermometer, I must say I like the FCST concept.

The chip might survive this operating temperature, but I doubt that the board will last long like this because of the physical stresses of expansion/contraction whenever the board is powered up or down.

Talking to RPF about this is a dead loss as they don't admit any problems (I can't anyway, having been banned for talking politely to Liz), but I'd like to know what Element 14 / Farnell's position is on this.  Should we try to extend board life by heatsinking the LAN9512 chip, or return it as faulty if Gert says that such high temperature is not expected?

Morgaine.

Morgaine, I just did the "finger switching" test again as I suggested. :-)

It seems my LAN chip is a bit hotter than I remember. I too can't get much beyond 5sec wtihout hurting my finger. It could also be that the outside temperature is now 25 degrees, while before it may only have been 20 degrees.

The "can't keep finger on" temperature is pretty much 52 degrees C. No matter who you are or if you say you have fire resistant fingers.

If the outside temperature rises, more heat will need to flow through your finger (less is being diverted by the PCB), and the hotter it gets. Even a 2 degree change might mean two out of two people now report unable to hold beyond 5 sec, while before it was "possible to hold indefinitively"

If you look at the datasheet, on page 41, it says you can expect a typical power use of about 763 mW.

http://www.smsc.com/media/Downloads_Public/Data_Sheets/9512.pdf

I don't pretend to be able to estimate the power-use within  a factor of two, so when I say "about 1W", this is certainly within range.

Regretably the thermal resistance isn't specified. The Texas instruments VCA8500 provides a "typical" value (i.e. a wild guess that it might apply to the lan9512), of 22 degrees / W. At 0.7W, that would mean only about 40 degrees C. We're seeing more than that.

But if the wild guess is off-by-a-factor-of-two, and it's 40 degrees/C for teh lan9512, then 60 degrees sounds like a possible value.

With the case at around sixty degrees, the inside will be only about 80 degrees. This is well below the maximum of 150 degrees.

Chips are built to work at these temperatures. Sure, I too have heard about some chips working themselves loose from thermal stresses. Before you complain to Farnell, the RPF or me, please wait until you KNOW it will fail because it HAS failed.

Some chips use a bit of power, and therefore they dissipate heat. That heat needs to be carried away and a temperature gradient is required before heat starts moving. This is simply the way things work.

Now usually these things are hidden inside a case. So you don't get to poke your fingers at it. The 'pi is open, As a learining experience YOU get to poke your fingers at it. Have you learned something today? That's the stated primary goal for the RPF.

Roger Wolff wrote:

 

Chips are built to work at these temperatures. Sure, I too have heard about some chips working themselves loose from thermal stresses. Before you complain to Farnell, the RPF or me, please wait until you KNOW it will fail because it HAS failed.

This is a technical site.  Questions and discussion are welcomed by Element 14, on both technical and product matters, and your suggested "wait until you KNOW it will fail" is not really helpful advice at all in an engineering community.

We can do a lot better than that, understand what is going on, and determine whether the board is being operated outside of its thermal spec (it's not device survival that's the worry, but the board/joints).  According to Gert, such LAN9512 temperatures were not expected at design time.

The board isn't failing yet, but if it wasn't designed for these thermal stresses then it won't survive them for long.  Element 14's input really ought to be sought regarding what we should do.  I  don't want my board failing on the day after warranty expires when the solder joints finally decide that they've suffered thermal movement long enough, and it's not in the manufacturer's interests for that to happen either.

And once they're in stock and I want to buy several Pi, I need to know that this common operating condition is within board spec before ordering.  (Model A is looking very attractive, the absence of LAN9512 making it more so.)

Morgaine.

I got some of these from SparkFun ...

http://www.sparkfun.com/products/10746

and waiting for these to try on the SoC ...

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=120820119736&ssPageName=ADME:L:OC:US:3160#ht_500wt_1180

-J

Adding a heatsink is certainly an option, but if it's required for board longevity then the heatsink should be part of the board design.

I have no shortage of small heatsinks here, but at this stage it's more a matter of establishing the principle with Element 14.  If they accept that it may be a good idea to add your own heatsink pending review of the situation with board designers, then they may want to advise accordingly since it could affect product warranty.

Agreed.

Also if by any chance, as reported before, due the wrong connection of the LAN9512 VDDCORE pin to the 1V8 rail the GPU is drawing some current from the internal regulator on that chip, it will surelly get hotter than normal.

Ethernet PHY's tend to run warm to hot, but this one seems to be slightly above of what I've seen before.

-J

Really, the chip is using a significant portion of a watt. On a 9mm x 9mm chip that's going to make it feel hot to the touch.

Once I have my "spare" pi, i'll see if I can find that 1.8V line and cut it.....

All measurements so far have indicated a significant powerdraw on the 3.3V line, and that mostly goes to the lan9512. And from there, it can't go anywhere but turn into heat.

There is a post on hackaday.com with someone who has added a heatsink to his 'pi.

That would be something hard to do given that it is two not contiguous pins that probably go to the power plane and you still need to keep the connection to the decoupling capacitors required for the LAN9512.

Unfortunatelly (once again the veil of secrecy) the Gerbers for the board layout are not publically available so it is difficult to tell by just looking at the two pictures of the boards without components how those traces are routed, that btw as far as I can tell are improperly routed since the trace is supposed to go straight from the pin to the capacitor.

I've seen the hackaday post, which motivated me to search for tiny heatsinks to try since I don't want to use the saw :-)

So far in my meter the Rpi shows 380-440mA draw now with the keyboard and tiny mouse connected and a NTSC TV monitor on composite video.

-J