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Old 23rd Jan 2019, 3:36 pm   #1
boombox
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Default PBX survives power cuts but not the power being switched off?!

I'm really confused...my PBX (a BT Inspiration) has survived with its memory intact a couple of 2-3 hour long power cuts over the past few years, and it's survived being accidentally turned off at the wall quite happily a couple of times - but yesterday I switched off the power at the switched fused spur and that was it. All settings and time and date forgotten. Any ideas why?!
It has no internal backup battery fitted and never has.
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Old 23rd Jan 2019, 3:44 pm   #2
julie_m
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Default Re: PBX survives power cuts but not the power being switched off?!

Were any exchange lines connected at the time the power was disconnected?
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Old 23rd Jan 2019, 3:49 pm   #3
boombox
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Default Re: PBX survives power cuts but not the power being switched off?!

Yep - but that's always the case - every time it's been disconnected from power - by whatever method
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Old 23rd Jan 2019, 4:43 pm   #4
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Default Re: PBX survives power cuts but not the power being switched off?!

If it's been preserving the time and date over power loss, it must have a backup battery of some sort in there, even if it's not obviously visible. I don't know the BT Inspiration at all, but perhaps it contains one of the integrated battery-backed RAM and clock modules which were popular in the late 1980s-1990s. They look like an overgrown chip, and the most popular ones were made by Dallas semiconductor. These days they're at an age when the batteries are failing, giving the symptoms you describe. They're a common failure point in a lot of test equipment of that era.

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Old 23rd Jan 2019, 6:03 pm   #5
JulietMike
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Default Re: PBX survives power cuts but not the power being switched off?!

The maintenance manual attached might help. It refers to a battery back-up on page 32.
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File Type: pdf Instn&Mtce.pdf (1.89 MB, 39 views)
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Old 23rd Jan 2019, 6:15 pm   #6
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Default Re: PBX survives power cuts but not the power being switched off?!

I think the battery backup is an optional lead acid battery to keep the phones powered.

The inspiration is vaguely similar to the old revelation, that used a supercap for power cuts.
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Old 23rd Jan 2019, 8:13 pm   #7
boombox
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Default Re: PBX survives power cuts but not the power being switched off?!

Interesting. I know there's no lead acid battery in there, so yes, a 'supercap' makes sense.

What doesn't make sense to me yet is why the 'supercap' discharged itself when the switched fused spur was switched off but doesn't seem to during powercuts EVEN when the powercuts go on for much longer than the few seconds I had the spur off for.

Thanks
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Old 23rd Jan 2019, 11:01 pm   #8
JulietMike
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Default Re: PBX survives power cuts but not the power being switched off?!

Attached spec from the system handbook for BT Inspiration shows that a supercapacitor is used for memory backup. Perhaps it has now failed.

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File Type: pdf BT Inspiration Spec.pdf (298.4 KB, 26 views)
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Old 23rd Jan 2019, 11:02 pm   #9
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Default Re: PBX survives power cuts but not the power being switched off?!

Boombox, you haven't said whether you have subsequently reprogrammed the unit and whether it now manages to retain its programming during power down.

Have you? Does it?

If all the settings are still lost / defaulted try reprogramming just one parameter or the minimum which will give some observable effect, and then power it off for a short time / a long time. Does it consistently lose the programming after either of those intervals?

If it does, whatever used to retain the programming during power down is no longer doing that.
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