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Re: power supply causing network failure?

On Aug 21, 2006, at 6:29 AM, Stuart Prescott wrote:

Hi all,

I have just bought a new power supply for my HP nx7010 laptop (the old one seems to have a broken wire on the low voltage side meaning it sometimes
doesn't actually deliver power... bad).

Unfortunately, the new power supply doesn't seem to work properly with the

The laptop detects that it has been plugged in to a power supply (LEDs change as usual on the front of the case) and the battery will charge up. However,
the built-in network card in the laptop (which uses the 8139cp driver)
doesn't work properly when connected to this new power supply. With the new power supply attached, I consistently have a 15-20% packet loss (making the network unusable); on battery or on my old power supply, I have 0% packet

The problem is persistent across reboots and there is absolutely nothing appearing in dmesg or any of the other logs to help me work out what is going on. I can make the problem go away just by unplugging the new power supply either from the laptop or the wall socket, but that's not really an option. I don't know whether the ipw2100-based wireless network is also similarly
affected as I don't have a wireless network where I am at the moment.

Has anyone ever heard of anything so strange? Any clues for a work- around?

It sounds like :
a) Your new power supply has a grounding problem, or a noise problem, thus introducing noise onto the Ethernet via the internal power bus. b) More likely - your old supply caused damage to the internal power filters and/or voltage regulators in your laptop and thus the Ethernet chipset is seeing dirty power when connected to your new supply.

Or a combination of the two, or something similar. Additionally some switching supplies throw a lot of RF noise, if your Cat 5 cabling is acting as an antenna at those frequencies, you could be "struggling through the noise" being created by the new supply.

I'd start with the simplest solution -- return the new supply and get a new one. After that, it gets a lot more difficult to do much. If you can find one of those Cat 5 cables with big round torroids built into each end (Cisco SoHo cheap routers used to ship with them, for example) you might try one of those to see if the noise clears up or gets markedly better. If not then the expensive fix (having a qualified service tech look into the guts of the laptop) awaits, probably.

If you still have the old supply and you find the *right* service tech who's actually had more than five minutes of electronics training, and isn't just a part-swap monkey, they might be able to figure out what damage would be most likely if the manufacturer actually gives them any schematics to work from... probably not nowadays... everything is "throw-away" or "field-replaceable units"... it's not cost-effective to troubleshoot to the component level anywhere but a bulk board repair shop anymore.

Nate Duehr

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