[cisco-voip] Strike 3 - Dead 7940G IP Phones

[Matlock, Kenneth L]

A few things I'd look at.

1) Is the PoE switch and the PC in the same building? (What I'm getting
at is if it's a separate building, you could be experiencing a
difference in ground potential from one to the other, and that's causing
excessive voltages).

2) Have you traced the cabling start to finish to verify it doesn't get
too near anything putting out large amounts of EMI? (Or maybe smaller
amounts over a longer period, if it's causing PoE power to spike above
the spec).

3) Have you ruled out the possibility of someone doing this maliciously?

4) Have you tested the cable using a Fluke (or similar) tester? (Not
just continuity, but pair lengths, crosstalk, etc). For this you may
have a bad infrastructure cable, and it's causing the switch or phone to
have to ramp up the power too high to compensate.

5) Are the PoE switch and PC both on UPS power? Possibly getting power
grid spikes in one side or the other that are traversing across to the
phone.

There are probably other things, but those are the ones I can think of
off the top of my head.

Ken Matlock
Network Analyst
Exempla Healthcare
(303) 467-4671
matlockk at exempla.org

-----Original Message-----
From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Micah Bennett
Sent: Friday, December 05, 2008 8:03 AM
To: cisco-voip at puck.nether.net
Subject: [cisco-voip] Strike 3 - Dead 7940G IP Phones

Well its been a few months since this issue happened to us.  Back in
July, Cisco ended up replacing the POE switch saying the issue was
probably a bad port there.  

Today, the new switch killed a third phone on the same port 12.  If I
plug a new phone in port 12 it works.  If I try the old one on port 12
or any other port, nothing - DEAD.

I find it hard to believe that this could be a problem in the POE switch
again on the same port.  I checked the third phone based off Davids
comments from back then.  I don't see any issues and moving the enet
cord does not help, but the phone switch sure smells like something
burned up.

These three phones are in a similar serial number range, but then again,
all of our phones are and this only happens at this network port.  

I am beginning to wonder if the NIC in the PC might be the problem and
its feeding back to they phone and smoking it.  

Any advice?

Thanks Micah.

----------------------------------------------------------

From: David Sullivan [mailto:David.Sullivan at barnet.ac.uk] 
Sent: Thursday, July 31, 2008 9:05 AM
To: Micah Bennett
Cc: cisco-voip at puck.nether.net
Subject: RE: [cisco-voip] Strike 2 - Dead 7940G IP Phones

Yes, we saw similar on a phone (though I can't recall which model, we
have 7912s and 7940s mostly) and it was down to a poor solder joint on
the ethernet switch pcb of the phone, some of the pins were connected so
the phone could source power but one of the ethernet pins was knackered.
We were able to get the phone working by wiggling the patch lead about
so it was quite obvious what it was from that, open it up and have a
look at that board though if you can't resolder it it might be a breaker
for spares now.

David.

-----Original Message-----

cisco-voip-bounces at puck.nether.net wrote:
> Waiting on my network admin to get in so I thought I would
> send this out and see if anyone has seen this before.
> 
> Tuesday morning 3:00am, a single IP phone (out of 200) on our
> network (being used by the single call center agent on that
> shift) loses connection to the network and shows "Ethernet
> Disconnected" on the phone screen.
> 
> We are using Cisco 3560 switches for our user network with
> POE from the switch.  Ethernet cable from the wall to the
> phone and from the phone to the PC.
> 
> Did not think much about it at that time, just figured it was
> a bad phone.  First one since our deployment last July.  I
> replaced the phone with a spare and sent the bad one back to Cisco
> under RMA. 
> 
> In testing the bad phone, it seems that the internal network
> switch is completely dead.  After the initial failure it
> showed "Ethernet Disconnected" on the screen so it was still
> getting POE from the switch.  When disconnected and moved to
> another network port, it will not come back on with POE.  I
> had to use a power cord to supply power and the phone still
> shows "Ethernet Disconnected".
> 
> Everything was fine all day Tuesday, and Wednesday.
> 
> Thursday morning, 3:00am, exact same problem on exact same
> network port, killing the replacement phone that was
> installed on Tuesday.  Everything is exactly the same even
> down to the time of failure.  Phone exhibits the exact same
> symptoms.  Was responding to POE but showing Ethernet
> Disconnected until disconnected from the network.  After
> disconnection, the unit only responds to power from a cord,
> and not POE.  Still shows Enet Disconnected.
> 
> Is the POE coming from the switch on this port killing the
> phone?  Has anyone seen anything like this before?	

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