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CordlessTelephone (Post Lightning Strike)

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StudentSA

Member
Hi Guys,

I would like to know if anyone can assist with the repair of a cordless telephone after lightning damage.

I have two base units and four phones. After a lightning storm the two base units power supply units stopped working. I purched new "wall warts" and they seem to come to life again. however as soon as I plug them into the phone line they hold the line.

Basically when I plug in the phone line and press the answer(green) button on the phone I hear a ring tone, which after a min or so goes flat no matter how many times I press the release(red) button the line is kept up.

Any ideas what I could check?

Kind Regards,
StudentSA
 

jpanhalt

Well-Known Member
Most Helpful Member
I had experience with a lightning strike in the US. So, this may not be applicable to you. First, disconnect everything plugged into the system. Then, find an old fashioned phone (one that is not electronic) and plug it into your system. Do you get a dial tone? If not, go to the service entrance box and see if you get a dial tone from the incoming wire. If you are cable, go to the modem. In the US, we have access to that box. If you can't get a dial tone there, then you need to contact the service provider. If you get a dial tone, then you need to find a pair of wires that are not vaporized and/or shorted in the house wiring. If you have a helper, it makes that search much easier. Once you get t he functional pair, use them for your wiring.

You might also want to open every wall box. Some of the damage to wires in our house were just in that box and was easily fixed. You may not be able to use the original colors, but that makes no difference.

If you don't have an old fashioned phone, use an electronic phone that is known to work.

John
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Waste if time - buy new ones.

Phones are particularly bad, as they get massive spikes via the mains, AND via the phone line as well.

Bin them and buy new, assuming you have household insurance you should be covered?.
 

StudentSA

Member
I'm inclined to at least try and fix them, They work 100% but the base unit keeps the line up ("off the hook")

When I plug the phone line into the base I can pick up the cordless an hear the dial tone, I can even make a call. The problem is that I cannot put down ("on hook") the call. It never releases the line.

I read up that when the line is in use a certain resistance is placed across the wires and on hook is another resistance. If there a specific component that I can look out for that does this function?

Thanks.
 

Menticol

Active Member
I don't think you will be able to fix the base's circuit board economically since modern phones are plenty of SMT components and non-replaceable integrated circuits.

Now, what about putting a switch between the cordless phone and its battery?

In theory cutting the phone's power will make the base think that the phone went out of range and then would release the line.
 
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rumpfy

Active Member
With the phone system, when the handset is 'off-hook', the line resistance is, I think, somewhere about 1100 ohm. Given the phone is a 48 volt system, this says a line current of about 40 mA or so. The voltage drop across the phone when in use is I think around 5 to 10 volt. When the handset is replaced, the line resistance has to increase quite markedly; I'm not sure of the value because it is not specified as far as I know. All these standards were based originally on the use a carbon granule microphones and old time British Post Office 3000 type relays. In those days the signaling current requirements were the limiting factor to customers line loop resistance.
The 'on-hook' resistance is usually considered to be at least 500,000 ohms.
I would be checking the line current in both on hook and off hook states. The on hook current should be smaller than one tenth of the off hook current.
Also, I am tempted to say that the approvals process for use of phones on a telecom network, would be that a relay is required for DC isolation of the line. I note you are in South Africa, and my guess is that the phone network is very much a BPO system. Is there a line relay and is it releasing, OR, is there an inbuilt 'lightning arrestor' (a VDR?) and is it OK.
I too have suffered lightning strikes on cordless stuff and to me I find it impossible to get inside the units to work on them. I can sympathise with both sentiments "buy new ones' and 'I'll try to fix them'.
Hope this helps.
 
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