Saturday, September 13, 2008

Cisco 7900 7941 hookswitch problems

Personally, I have found more failing hookswitches on 7941 phones than I am comfortable with. The symptom is a fully functioning phone if you use the speaker phone, but the inability to go off hook on, or to switch to the handset.

The official Cisco document entitled "Best Practices for Cleaning and Troubleshooting Cisco IP Phone Hookswitch" indicates the hookswitch is self cleaning, and the contacts use a "wipe action" to self clean the contacts. The suggestion is to flash the hookswitch rapidly "a dozen times or so to clean the contacts".

It appears that a.) they likely have a problem with their hookswitch design, given they have a special document to assist in troubleshooting them, and b.) either their documentation is incorrect, or they have re-engineered the hookswitches.

Here's the hookswitch I found inside my 7941:

I don't see anything self cleaning or wiping about it.

What it is is one of those collapsing rubber nipples that short a contact on a circuit board below it when pressed. Yuck. When the handset is on hook, the nipple is not pressed, so I can't imagine it wearing out. It is at rest most of the time. I also can't see it being affected by the environment (dirt, humidity, etc.) since the rubber nipple seals the area where the contact is made.

The single wire loop in the picture is actually the spring that actuates the hookswitch. Yuck.

PLEASE NOTE: I am not an employee of Cisco, nor am I authorized by anyone to repair Cisco phones. Read at your own risk!

You CAN disassemble a 7941 fairly easily if fixing it yourself is your only option. Please check with your telecom support staff or Cisco partner before to examine other options first.

1. Unplug all the cables from the phone (Ethernet, headset, handset, power, etc.).

2. Remove the footstand from the phone.
a. Press the large button on the side of the phone to recline it all the way.
b. Flip the phone to view it from the back.
c. Use a screwdriver or like to push two "sliders" to the center of the phone. They are located in a groove at the bottom of the footstand, just above the "AUX" port and headset port. These can be quite difficult to move, but when you do, the footstand should fall right off.

3. Remove four phillips head screws from the back of the phone. Two are recessed and previously covered by the footstand. The other two are under the rubber feet at the bottom of the phone. If you take care when peeling off the rubber feet, they can be reattached with the adhesive that remains on them.

4. At the bottom of the phone, separate the front and rear portions of the phone by about a half inch or so. You do not have to separate them more than is comfortable. DO NOT try to break the phone wide open, like a clam.

5. While separated, pull the back of the phone "down" and the front of the phone "up", as if you are separating an Oreo cookie. The idea is to disengage plastic hooks holding the front and back together. If you open the phone like a clam, they will break. You will need to slide the front and back pieces in separate directions about a half inch. If you do it correctly, the front and back will now separate easily.

From there I would suggest:

1. Disengaged one end of the wire spring and straighten it out slightly. When reinstalled, this will create extra pressure on the hookswitch when off hook, creating extra pressure on the rubber nipple thing, and potentially making contact with the circuit board that wasn't being made before.

2. Remove and fiddle around with the rubber nipple. There are 4 rubber tentacles that poke through the circuit board, holding the rubber nipple on. Since it's difficult to get them back through the board, I suspect that they may not have been installed with much care originally. If the nipple wasn't tight against the board, it wouldn't make contact with the circuit board when the phone was off hook.

Steps one and two above ultimately provided me with a once again working hookswitch.

17 comments:

  1. Anonymous8:13 PM

    Needed to clean the number key pads on the phone and this explanation on how to dismantle phone helped greatly

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  2. Anonymous4:56 PM

    This was a great help, thanks! Cleaning was not enough for me, though. I ended up taping a square I cut from a business card between the plastic plate on the hookswitch and the rubber nipple to have it apply more preasure.

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  3. Anonymous8:39 AM

    As a Ph.D. (Phone Doctor, I approve of this article on the treatment of LSS (Lazy Spring Syndrome). This can usually be done as an out patient procedure with a release given to return to normal activities without restrictions after a short recovery time in PACU / ICU. Post operative follow up is recommended after 6 months but most patients do not need additional care. MD, Ph.D.

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  4. Anonymous12:03 PM

    You actually Don't need to take the footstand off the phone, to get it open. Just press the side button to lift it up, unscrew the 2 screws, then put the footstand back down and unscrew the 2 under the rubber feet and you can go from there. Makes it a little easier not having to push those clips over on the footstand :)

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  5. Anonymous7:42 AM

    works for me, thanks

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  6. Anonymous4:22 PM

    Thanks for the info, worked great.

    ReplyDelete
  7. Excellent information, helped me fix 2 phones that had been screwing up for months. Thanks!

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  8. We've had a huge amount of phones doing this, we've just RMA'd them. POS in my opinion.

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  9. Basir5:58 AM

    Here you can read more and it helped me very much:
    http://www.nelsonet.net/wordpress/?p=162

    ReplyDelete
  10. Anonymous5:21 AM

    Excellent article, lots of help in dismantling handset.
    Thank you! B-)

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  11. Anonymous8:47 AM

    You can use the end of the wire spring to re-insert the rubber hook switch back into the 4 holes. Works great. (or the end of a paper clip)_

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  12. Anonymous1:43 AM

    I got a 7941 from a local surplus shop here in the Philippines, after getting it updated to SIP firmware and configured to work with my VoIP router this was the last step to got the phone up and running. Thx a lot. I am happy now to have a world class phone for just 20$. Chris

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  13. Anonymous7:05 AM

    Genius. We had some phones not engaging the dial tone when the receiver was picked up, due to the faulty hookswitch. Re-tensioning the pressure wire was enough to fix it for me. Good explanation also of how to take the phone apart without damaging it. 10/10.

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  14. Anonymous6:41 AM

    Thanks for this, worked like a charm!!!

    Shawn

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  15. Anonymous3:50 PM

    God i hate this phone. With mine, it seems that the plastic hook switch has become warped over time. You need to apply slight pressure on the switch towards the screen in order to get it to trigger the phone. i have about 10 phones doing this out of aprox 100. very annoying. However yes I have fixed it by taping a small piece of a business card to the ringer switch. this makes up for the warping of the plastic i think. i also straightened the spring

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  16. Anonymous4:32 PM

    I have never separated an Oreo cookie that way, but I eventually got the phone apart.

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  17. Thanks for the good dis-assembly instructions :)

    As already mentioned...

    1) Removing the foot stand is not necessary

    2) The little rubber 'tentacle' nipples can be easily re-inserted into the PCB by putting a straightened paperclip into the back of them, as they are hollow, and -gently- pushing them back into their respective holes.

    ReplyDelete