cisco 7920 static crackle noise

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Dec 13th, 2010
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cisco 7920 ip phones (2)

firmware: 7920.4.0-03-02

hardware info 4.0

cisco 1242AG access point

System Software Version: 12.4(10b)JA3

cisco 2651XM router

IOS: c2600-adventerprisek9-mz.124-15.T9.bin

I have a couple of cisco 7920 phones, they are connected to a cisco 1242AG access point which is in turn connected to an NM-16ESW switch in a cisco 2651xm router. The problem is noise and static on both phones and happens with both internal and external (sip trunk) calls. I also have 7940 desk phones on the same router but they do not have any noise problem. What's really weird is if I squeeze the 7920 phone while it's at my ear the static and crackle increases. I tried a different voice codec in the router but it made no difference and I've always used g711ulaw. I also have 'no vad' on the dialpeer.Can anyone shed light on this?

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pmickelsen Tue, 12/14/2010 - 10:20
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We've had a number of these.  There were some failures in the antenna solding, as well as speakers and mics.  We rma'd 6 phones out of 140 in production some weeks.  There were never fewer than 1 a week.  If you have smartnet, open a case, it will likely be replaced.  The 7921's are much more stable.

tonyspcrepairs Tue, 12/14/2010 - 10:42
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thanks for your response. I thought the crackle was caused by a wrong config in either my AP or router but maybe tyou're right it could be poor solder joints. I'm currently searching for a support contract for this phone but it's like trying to get blood out of a stone.

pmickelsen Tue, 12/14/2010 - 10:49
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If it had ever worked with any 7920, it should be the phone.  If not, it might be the config.  Try a different 7920, if available.  We had them on 350 ap's with no special voice config on the wireless side, and no issues, except hardware on the phone.

tonyspcrepairs Tue, 12/14/2010 - 11:07
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actually I do have another unused 7920 in the drawer.I tried it and whaddya know, practically no crackle, so it must be the phone. I've been trying on and off for weeks to get a support contract, maybe I'll have some luck in the next few days. I can't afford a 7921 so hopefully I can rma this dodgy 7920 I have.

pmickelsen Tue, 12/14/2010 - 11:15
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No guarentees, but I would try calling Cisco tac and saying you heard there was a manufacturing defect on some 7920's.  And would like to see if it can be replaced.  The phone is almost unused and seems to have audible crackle and wireless connectivity issues.  The other 7920 does not.  They might replace it for you.  Our customer got a very good subsidized deal on replacement 7921 phones.  Again, no promises, but some of these were broken with minimal to no use, repeatedly.  As it is eol/eos, you should not be able to get a support contract anymore.

Best of luck, never hurts to ask.

paolo bevilacqua Tue, 12/14/2010 - 11:35
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If you can't get an RMA, bring the phone to an electronic repair shop. They may redo the cold solderings and fix it for 10 quids.

tonyspcrepairs Wed, 01/26/2011 - 09:47
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I found a solution for this which may benefit others....

I took my worst 7920 phone (really bad crackle) and dismantled it.  There are two circular bullseye-type contacts at each end of the phones' circuit board. One connects to the ear speaker, the other to the microphone. I got some isopropyle alchohol and cleaned these contacts thoroughly. I also cleaned the back of the microphone piece (it has three contact dots on it) and the spring contacts for the earpiece. While there I also bent the earpiece contacts up a bit so they'd press harder when re-assembled. I also cleaned the contacts on the battery for good measure. Re-assembled - the phone is like new, sound is perfect, no more crackle.


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