Is my Pi broken?

As a guess, I would first suspect that an iffy solder joint failed after thermal cycling.  USB crystal X1 is a likely suspect because RasPi forum users have reported problems with that part and have had success resoldering it.  X1 is most likely hand-soldered, and if so it's more likely to be poorly soldered than reflow-soldered parts.  In any case, I'd check the return policy right away so you don't miss a deadline.

An alternative possibility is that one of the peripherals has developed a fault, especially if in between distributions they have stayed the same. Can they be tested on another machine, althought this wouldn't be conclusive as the machine might be more tolerant of extra current draw that the Pi might not.?

It could be the X1 soldering (I don't feel confident enough to try reflowing it). From what I've seen of reported problems, though, the USB port just fails to work altogether rather than doing what mine is doing.

As I've tried it with and without peripherals attached, including a different (wired) keyboard, a peripheral fault doesn't seem likely.

Mike,

   Farnell/element14 has been very good about replacing non-working

units.  They pay for shipping, and have units reserved for this purpose,

so you don't have to wait in line.  Just ring them up.  The procedure is

called RMA.  You aren't expected to do any soldering yourself, and

it sounds like you've done plenty of troubleshooting, especially since

your peripherals worked originally.  It's valuable for them to see

faulty units so they can analyze the causes, which makes it valuable

for future customers as well.

There is also an online RMA form here:

http://uk.farnell.com/jsp/support/support.jsp?formpage=farnell/en_UK/support/help/return_form.jsp

I would suggest trying another power unit first of all.

The RPi is notoriously flakey about its power requirements.

There have been several postings around the web where odd problems have been found to be due to thew power unit.

If you are using a standard wall-wart type of thing then ditch it and get a good power unit as there's no point spoiling the ship for a ha'porth of tar as the old saying goes.

I am running my Pis on Samsung micro-usb power units from Galaxy phones and have had no problems at all.

Right, just sorted out the return on the phone. I'd had a look at the online returns form but it seems more geared to returning incorrectly ordered or supplied items than returning defective ones.

As regards PSUs, the one I'm using is an unbranded iPhone replacement charger supplying 5V 1A. Also tried with a charger for a Sony mobile (which has lower current capacity) with similar results. As the original PSU had happily powered Pi plus keyboard for hours, if not days, it's probably up to the job.

I got the replacement, which behaved exactly the same as the one that had just been replaced.

Just in case, I bought another PSU - one from Amazon which is in the Wiki as working. Same results.

So then I swapped the microUSB lead for the one off my phone. Worked straight away.

This puzzled me, until I remembered that I had initially had the Pi working with one microUSB lead. I then put it in a case (the SLUG acrylic one) but the hole for the microUSB plug was too small for the one I was using, so I used another one. And that was the bit that I'd completely forgotten. So I shall kick myself fairly gently. Thanks for everyone's help, I wish the solution wasn't quite so embarrassing...

Thank you for reporting back and sharing your experience. It is really useful to know what is the source of problems and what takes to correct or work around them.

-J

Sadly this isn't an uncommon problem in other devices either. The Samsung Galaxy S phone is notoriously choosey on its micro USB cable.

I had a batch from one supplier of which none worked (I got my money back) and they turned out to be fake Samsung badged leads which Samsung had become aware of.

It seems that the screening and cable diameter is the problem so I guess that the same thing applies to the RPi