I can’t explain this – can you?

[Gary WoodingParticipant @garywooding25363]

[Gary WoodingParticipant @garywooding25363]

I've had a set of 4 DECT cordless phones for about 13 years. They all worked fine until one day, about 3 months ago, when I accidentality knocked a charging station and handset off the shelf. When I put the handset back on the charger it was totally dead. Putting a good handset on the charger confirmed it was OK, and putting the dead handset on a good charger confirmed it was dead.

I took the handset, charger, and a known good charger, to a friend who used to be an active radio ham. After confirming it was really dead he took the covering off, expecting to find a break or some other physical reason for the failure. He found nothing. The design layout was such that it wasn't possible separate the several PCBs for more extensive problem hunting so his advice was to scrap it and either make do with three handsets, or buy another set of four. I decided make do with three. Until, you've guessed it, I accidentality knocked another one off the shelf and was dismayed to find that, it too, was totally dead.

So I purchased another set of four and copied the phone book entries from the old phones to the new ones and started to delete them, one at a time, from the old phones so that the two remaining handsets could be salvaged and used by someone else. I was interrupted many times in this endeavour and got somewhat muddled up because I discovered that I was actually removing entries from one of the broken phones. What? How could I remove entries when the phone was totally dead? I checked all four handsets, and all four were working!!!

What's going on here? Those two handsets were truly dead – totally inert. I'd done nothing to them and now all four phones are working properly. How come?

[David JuppParticipant @davidjupp51506]

It was buying the new ones that 'did it'.

[pgk pgkParticipant @pgkpgk17461]

When we were faced with a lame horse and investigation failed to find a cause, then the ultimate answer was to take the shoes off and turn it out into a field for 6 mths. Almost always worked.

pgk

[Martin KyteParticipant @martinkyte99762]

Same as the closer you get your Granny to the Doctors the better she feels.

;O)
Martin

[Frances IoMParticipant @francesiom58905]

poor contacts on the battery connections? – I’ve had similar problems with remote controls as often one terminal is difficult to reach

[Anonymous]

Consumer products often use conductive rubber strips (aka Zebra strip) to make connections rather than a physical connector. They're very common on displays. If the strips get knocked they may distort enough to lose contact. But being rubber over time they can return slowly to their original shape, thus restoring contact.

Andrew

[roy entwistleParticipant @royentwistle24699]

It's the same elves that keep hiding tools in the workshop

Roy

[J HancockParticipant @jhancock95746]

Yep, had the same thing with an electric lawnmower.

Recharged battery , tried every trick 100 times over 4hrs , nothing.

Placed an order for new one.

3hrs later and tried the old one again, worked first time !

[noel shelleyParticipant @noelshelley55608]

Andrew could very well be right ! The phones were NOT dear, they just couldn't tell you so, their communication with you had failed. The zebra strip ! I have found devices that though seeming dead, on removing the strips and refitting them the work fine . Noel.

[Gary WoodingParticipant @garywooding25363]

I like Andrew's suggestion – it seems very plausible. And makes sense.

[not done it yetParticipant @notdoneityet]

Posted by Gary Wooding on 28/11/2021 13:29:08:

I like Andrew's suggestion – it seems very plausible. And makes sense.

He’s both clever and practical!

[SillyOldDufferModerator @sillyoldduffer]

Another possibility is an automatic factory reset eventually triggered after a microcontroller's memory was scrambled as the battery vibrated between the spring connectors due to being dropped.

Many ordinary electronic products contain microcontrollers because they allow complex physical circuits to be replaced with software. Functions are done in software rather than a complicated printed circuit board full of conventional components. Considerable savings are possible because microcontrollers can be had for under 10p each, and their brains also make it possible to add all sorts of bells and whistles. (Not always a good thing! The poor old user often ends up with a difficult to follow menu system and incomprehensible manual.)

A microcontroller's program or configuration can be corrupted by bad power supply, alpha-particles, software bugs, lightning strikes, condensation or RFI. Therefore, quite common for devices to have a Factory Reset function triggered by pressing a reset button or secret key sequence or automatically after a long power down or detecting 'not responding'.

Taking the batteries out for a long time is always worth trying. As some microcontrollers only consume a few microamps, they might carry on for several days on internal capacitors after the battery is removed.

Dave

[Author]

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