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Old 27th Jul 2021, 9:06 pm   #1
Jim_746
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Default Faulty BT 2+8

I have a BT 2+8 PABX that has sat unused (in the house) for several years and I have recently pulled out of storage. It would appear that it has developed a fault whilst in storage.

On plugging in the BT 2+8 there was no click from the relay, which I expected to hear a couple of seconds after applying power. On lifting an extension handset there was no dial tone, only the sound of mains hum. This is the case on all extensions, with some also having a irregular clicking sound. Extensions are powered -- those with DTMF can produce tones but there is no response from the BT 2+8 on attempting to dial another extension.

I haven't a clue where to start. Does anyone have any thoughts?
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Old 28th Jul 2021, 8:40 am   #2
Nickthedentist
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Default Re: Faulty BT 2+8

Is there a backup battery, either accessible or soldered to the PCB?

A quick Google talks about a "lithium battery", probably like you'd find on a PC motherboard.
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Old 28th Jul 2021, 10:51 am   #3
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Default Re: Faulty BT 2+8

Hello Nick,

Yes, this is an 'Enhanced BT 2+8' with 3 V battery backup. I probed across the battery and got a reading of about 100 mV.

There is a DIP switch option to enable or disable battery backup. However it has no effect on the current (non)operation of the system, with symptoms remaining the same regardless of the battery backup switch state.

Given the age of the unit I assume that the back up battery was flat before I put it into storage and it was fully operational then.
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Old 28th Jul 2021, 11:34 am   #4
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Default Re: Faulty BT 2+8

There's a BT engineering note that says that the exchange line(s) must be present when powering up otherwise extension 20 and 21 will 'lock up' and not work properly. Might be the case?

We had 2 BT2+8's here (mk1's) and I got sick of their quirks and random glitches, so installed a Panasonic and never looked back.
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Old 28th Jul 2021, 12:56 pm   #5
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Default Re: Faulty BT 2+8

The 2+8 system-phone has more than a passing resemblance to those used with the Philips Sopho K series.

https://www.britishtelephones.com/bt2plus8.htm

https://www.britishtelephones.com/sophk8.htm
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Old 28th Jul 2021, 7:18 pm   #6
WayneL74
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Default Re: Faulty BT 2+8

Inspired to help I dug out my 2+8 E to take a look.

It does have a battery - soldered onto the board. This will be dead by now.

I powered up & was greeted with the same issues as the OP.

McMurdo is correct - without a line connected to EXCH1, EXT20 will not initialise. The same goes for EXT21 if EXCH2 is not connected if the system is configured for 2 lines.

The way around this for testing is to flip DIP switch 8 of the configuration bank up. This tells the system no lines are attached. Also be sure to power cycle after this as it only reads the switches at boot up. I have attached a photo of my settings with no lines connected.

Also worth flipping switch 7 down as if the battery has a little charge left it might cause the system to remember some corrupt settings when you power down & up which won't help.

I was still getting odd things happening - couldn't seize an exchange line although there was one connect etc. I then moved all the configuration switches up & down a few times each, power cycled again & all seemed well.

If you look at the 2+8 link posted by Rambo1152 & select the programming link it gives you all the DIP switch settings.

Hope this helps.

Regards,

Wayne
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Old 28th Jul 2021, 8:11 pm   #7
Jim_746
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Default Re: Faulty BT 2+8

I have never had any exchange lines connected to my BT 2+8, so I've always had it programmed as 'no lines connected' via the DIP switches. The lack of connected exchange lines had never been an issue in prior use.

I put all the DIP switches through a few on/off cycles earlier today, suspecting dirty contacts to be causing the problems, but to no avail. I tried the same maneuver this evening and it's fizzled back into life, quite literally - I powered it up again, picked up an extension, and was met with hum followed by a crescendo of static and then suddenly dial tone returned.

It looks like another case of dirty contacts rearing their ugly head again.
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Old 28th Jul 2021, 9:06 pm   #8
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Default Re: Faulty BT 2+8

It sounds like a drop of switch cleaner judiciously applied to the switches might be a good idea.
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Old 28th Jul 2021, 9:54 pm   #9
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Default Re: Faulty BT 2+8

I wonder if it's a high esr capacitor that didnt like being put on furlough for so long, I'm getting alot of that in my day job at the moment as things get powered up again.

The 2+8 and sopho are both philips-made of course as was the Renown, another little PABX that seems to suffer random glitches....
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