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FYI: Cisco 79xx Handset Hook-switch sensitive to bright light causing unexpected hang-ups.

Hi All,

This is purely an FYI type post because I think it could be of help to some folks that might have experienced this without realizing the cause.

I'm also posting it because any time I've described it to industry folks they say they've never heard of it.

One day while speaking on my 7945G I began getting dropped calls. It was almost impossible to maintain a call for more than a few seconds.The phone simply behaved as if I'd ended the call by replacing the receiver.  It was a time of day when extremely bright low-angle sun was entering my office.

Long story short, I realized that the phone went on-hook whenever the bright sun hit the base just right.  I could control when the phone would go on or off hook simply by casting a shadow over the hook-switch or, more specifically, the gap between the base and the hook-switch.

You can replicate this with a bright flashlight.  Simply take your phone off-hook and shine the flashlight into the gap between the base and hook-switch and you should be able to make the phone go on-hook. Remove the light and the phone should go back off-hook.

This was very perplexing to me until I realized it was some optical component in the base housing that was reacting and not something on the surface of the phone.

I hope someone sees this and it helps explain odd behavior in their environment. I think it's just something that is good to know about the design of these handsets.



VIP Advisor

FYI: Cisco 79xx Handset Hook-switch sensitive to bright light ca

Thank you for sharing your experience with this; it is very helpful!

Anthony Holloway

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