Why can't I get the networking to work

[Madrilleno]

It seems you are loosing about the amount of voltage I would expect if you have a non recovered F3 polyfuse. Please measure across the polyfuse (F3 on the back of the board) to see if you are losing a good part of a volt over it. It would explain why you cannot get the voltage level between TP1 and TP2 to a reasonable level, that is at least 4.85V.

Nope, 200mV.

[obcd]

Looks like a faulty board.
It's kind of strange that you can't obtain a dhcp wireless as well.
Have you tested this on the working board with the network cable disconnected?
You really have bad luck with your power supplies..

[Madrilleno]

Yep, it really bugs me that I only have problems with the NW devices. I would put it down to a fault on the USB connection to the wired ports, but it's the same for a wireless connection on a USB hub OR straight into the built in port.
Anyone know of a (cheap) USB to cat5 adaptor which will work on the Pi?

[mahjongg]

It seems you are loosing about the amount of voltage I would expect if you have a non recovered F3 polyfuse. Please measure across the polyfuse (F3 on the back of the board) to see if you are losing a good part of a volt over it. It would explain why you cannot get the voltage level between TP1 and TP2 to a reasonable level, that is at least 4.85V.

Nope, 200mV.

Not nope, yes! 200mV is "a good part of a volt" one fifth of a volt.
0.2 Volt loss is significant enough. It would turn a perfect power supply 5.00 V into a more marginal one (4.80 V). Also if the polyfuse was normal, it would be about 0.2 Ohm, but that would mean that you have 1000mA (1A) running through it! I would expect 100mV drop over F3 in a normal situation. So either you are running more than a normal amount of current through F3, or its resistance is abnormal 0.2 Ohm is a good fuse, and 0,45 Ohm is a fuse an hour after it has tripped. Your fuse looks more like the latter than the former.

Its also possible you have some loss in the USB cable too.

[Madrilleno]

It seems you are loosing about the amount of voltage I would expect if you have a non recovered F3 polyfuse. Please measure across the polyfuse (F3 on the back of the board) to see if you are losing a good part of a volt over it. It would explain why you cannot get the voltage level between TP1 and TP2 to a reasonable level, that is at least 4.85V.

Nope, 200mV.

Not nope, yes! 200mV is "a good part of a volt" one fifth of a volt.
0.2 Volt loss is significant enough. It would turn a perfect power supply 5.00 V into a more marginal one (4.80 V). Also if the polyfuse was normal, it would be about 0.2 Ohm, but that would mean that you have 1000mA (1A) running through it! I would expect 100mV drop over F3 in a normal situation. So either you are running more than a normal amount of current through F3, or its resistance is abnormal 0.2 Ohm is a good fuse, and 0,45 Ohm is a fuse an hour after it has tripped. Your fuse looks more like the latter than the former.

Its also possible you have some loss in the USB cable too.

Sorry, Mahjongg, you are chasing smoke on that. Remember, earlier in the post I said that I had powered the board straight on to the GPIO pins @5.07v with the same result (no connection). So the state of the polyfuse is not significant to the original problem. I have two other boards which run with no problems with all of the power supplies I have tried.