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Old 10th Jul 2018, 12:58 am   #1
Skywave
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Question Info. on 'phone requested

This post may be in wrong section: if it is, my apologies; please move it accordingly.

The manufacturer of this 'phone no longer exists - so to me, it is a 'vintage 'phone', albeit one that it uses modern technology.
Manufacturer is 'Answercall': underneath this 'phone there is a London address. So it is (presumably) of U.K manufacture.
Model is a 'Trojan'; name 4000.

To the best of my scant knowledge of 'phones, I think this 'phone qualifies as a 'feature phone'. Amongst its facilities, it has buttons and switches for:
Program / Normal; Tone / Pulse; ON / OFF; Monitor high / low; earth recall / time line break and ten push buttons which I assume are for storing frequently used telephone numbers. The insides are full of chips, etc., but there is no battery . (So where does the voltage for the embedded electronics come from?)

I connected it to my incoming land line and yes, it does dial out and receive calls.

I'd like to get the maximum use from this 'phone: to do that, a copy of the manual would be useful and / or any info. members might be able to provide for me.

Can anyone help with this, please?
Thank you,

Al.
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Old 10th Jul 2018, 9:46 am   #2
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Default Re: Info. on 'phone requested

If there's no sign of any power connector, it must be line powered. A small amount of current can be drawn from the line before an "off hook" condition is tripped. CMOS electronics takes very low current unless it's busy doing something, occasional heavier currents can be had by using a storage capacitor charged via a suitably high resistance.
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Old 10th Jul 2018, 10:48 am   #3
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Default Re: Info. on 'phone requested

Answercall was primarily an answering machine company but they did sell conventional phones as well, powered by the phone line. You are right that the memory buttons can be programmed with phone numbers. The programming sequence will be something like <program><memory button>01234567890<program> but that's just a guess and the sequence may be different, e.g. <program>01234567890<memory button>.
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Old 10th Jul 2018, 1:47 pm   #4
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Question Re: Info. on 'phone requested

Thanks. "Powered by the phone line": I thought as much, but wasn't sure. This 'phone will connect to the 'phone socket of a broadband / ADSL filter, so although there is a BT431 plug on the 'phone lead, there will only be the twisted pair of wires to the 'phone. Presumably, I can power it from an external d.c. supply - but what voltage should I use? 50 v.d.c.?

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Old 10th Jul 2018, 2:49 pm   #5
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Default Re: Info. on 'phone requested

Quote:
but what voltage should I use? 50 v.d.c.?
Use 12V d.c., Al - 50V is what is present before the loop is made, and the voltage across the instrument then drops to (typically) 12V. Don't apply a constant 50V across it! As said, the line voltage is sufficient to power telephone memories using CMOS without the need for an external supply.
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Old 10th Jul 2018, 4:18 pm   #6
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Default Re: Info. on 'phone requested

I think I had one of these back around 1995. If I am correct, it did work well but annoyingly lost its memory when unplugged (no battery backup). Hope yours is different.

Ken
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Old 10th Jul 2018, 8:40 pm   #7
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Default Re: Info. on 'phone requested

Quote:
Originally Posted by Skywave View Post
Thanks. "Powered by the phone line": I thought as much, but wasn't sure. This 'phone will connect to the 'phone socket of a broadband / ADSL filter, so although there is a BT431 plug on the 'phone lead, there will only be the twisted pair of wires to the 'phone.
That's all it will need.

Where were you thinking of connecting an additional power supply?
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Old 10th Jul 2018, 9:17 pm   #8
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Arrow Re: Info. on 'phone requested

My thanks to everyone for all the above.

As I stated in my OP: "To the best of my scant knowledge of 'phones . . . "
I was (still am?) under the impression that with a twisted pair connection, there is no voltage across that pair - simply tones received or produced plus speech. That's why I expected it to be necessary to provide an external d.c. supply.
However, the post above from OscarFoxtrot seems to contradict that.

This 'phone does not have a battery backup.

Al.
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Old 10th Jul 2018, 9:48 pm   #9
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Default Re: Info. on 'phone requested

Quote:
'...under the impression that with a twisted pair connection, there is no voltage across that pair'

There is a nominal 50V d.c. voltage on the line. When the handset is lifted, a loop is made and the current operates a relay at the exchange. A d.c. excitation current is then applied to the subs' telephone to energise the carbon mic (used to good effect by memory storage and, in some cases, speaker amplification and the illumination of an LED). The line-length may present a resistance of 1 kilohm or so.


The audio tones and speech are superimposed upon the d.c. excitation voltage and bridged off through capacitors at the exchange, with the excitation voltage fed to the telephone via a bridging coil (relay) steering the a.c. speech and tones one way and the d.c. another.


The above is very simplistic!
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Old 10th Jul 2018, 10:58 pm   #10
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Arrow Re: Info. on 'phone requested

Thank you! That indeed may be "very simplistic", but most of that I did not know. However, progress has now been made.
The incoming land line is run to my desk, where the ADSL filter, router and existing 'phone (and computer) are located - as below . . . .

Incoming line ▬ OR Master Socket type 5C ▬ cable to ADSL filter: O/P 1 = feed to 'phone; O/P 2 = feed to router.

When I plugged this phone-under-test into the 'phone O/P of the ADSL filter, I could dial out and receive calls, but no other functions on the 'phone worked.
However, when I plugged this 'phone into the OR Master Socket instead, things came to life. An investigation has revealed that the cable from the OR Master Socket to the ADSL filter is a twisted pair only. Thus there is no line voltage to the 'phone when it is plugged into that ADSL filter.
So it seems to me that if I wish to use this 'phone on my desk, that cable will need to be replaced by a four (or six)-wire cable, or re-locate the ADSL filter to the Master Socket and then run separate cables from it to the router and the 'phone: doing either will not be difficult; the first option will be the easiest.

If there are any misunderstandings in all of that, I'd appreciate being told accordingly: thanks.

Al.
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Old 10th Jul 2018, 11:09 pm   #11
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Default Re: Info. on 'phone requested

Your phone probably uses a capacitor to preserve the volatile memory if unplugged for a few minutes. Maybe an hour or more if you're lucky.

<Edit> just seen your latest post, and that is strange. It shouldn't matter where you plug it in.

There could be an issue with an old phone not ringing on a particular socket but that isn't usually a problem at a master socket or ADSL filter (and that's not the problem anyway)
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Old 11th Jul 2018, 12:18 am   #12
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Default Re: Info. on 'phone requested

There'll only be two wires, ie one pair, coming into your house. Internal wiring may use four-core cable but one is only used for ringing and one isn't used at all.

The only thing I can think of in your situation is that the first socket and filter you tried have a higher resistance than the Master Socket meaning there isn't enough current available for the 'phone's "extras." If there was no DC it wouldn't work at all.

You say "Thus there is no line voltage to the 'phone when it is plugged into that ADSL filter." Have you verified that with a voltmeter? There should be about 50V there if no telephones are off-hook and if you lift one it will drop to about 10V.
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Old 11th Jul 2018, 10:30 am   #13
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Default Re: Info. on 'phone requested

Could the twisted pair lines be transposed giving wrong polarity dc? Shouldn't matter for the phone but might for the added functions.
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Old 11th Jul 2018, 1:29 pm   #14
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Default Re: Info. on 'phone requested

Quote:
Could the twisted pair lines be transposed giving wrong polarity dc? .
Pretty sure there'll be a bridge-rectifier across the line feeding the ancillary circuits, given that line polarity can change arbitrarily or determined by switching sequences, without ill-effect.
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Old 11th Jul 2018, 11:18 pm   #15
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Arrow Re: Info. on 'phone requested

Quote:
Originally Posted by ThePillenwerfer View Post
There should be about 50V there if no telephones are off-hook and if you lift one it will drop to about 10V.
Yes: I have now verified that: thank you. However, I have now reached the conclusion that the source of the fault is in the 'phone itself - an intermittent fault. (I acquired this 'phone via Freecycle: that may be relevant. I have a need coming up soon for another 'phone here).

This 'phone has a push button labelled 'ON / OFF'. When in the OFF position, it functions as an ordinary 'dumb' 'phone. When in the ON position (an LED lights) and an incoming call is received, placing the 'phone down on its rest results in the call not being terminated but the sender's voice emanates from the built in speaker. That is when the fault is not present; when it is present, that voice from the speaker is absent. (I wonder if this 'phone has a corresponding microphone, thus enabling 'hands-free' operation? )
So, to me, this fault sounds like typical 'sticky switch' syndrome: either the ON / OFF switch or the 'phone handset down' switch.

What does not help, of course, is that my 'diagnostic' tests and conclusion are based on a fair degree of inspired guesswork, since I do not have the user's operating manual. But the info. I have received (as above) has been a real help: thank you.

Aside: I am yet to investigate what I believe are the stored numbers memory buttons. To me, it seems sensible to clear the above fault first.

Al.
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Old 11th Jul 2018, 11:22 pm   #16
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Arrow Re: Info. on 'phone requested

Quote:
Originally Posted by Herald1360 View Post
Could the twisted pair lines be transposed giving wrong polarity dc? .
Quote:
Originally Posted by russell_w_b View Post
Pretty sure there'll be a bridge-rectifier across the line feeding the ancillary circuits, given that line polarity can change arbitrarily or determined by switching sequences, without ill-effect.
I did open the 'phone up, early in my investigations. I did see four diodes on the pcb that were located near to where the incoming line meets that pcb.

Al.
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Old 12th Jul 2018, 1:05 am   #17
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Default Re: Info. on 'phone requested

It's normal for phones of this type to develop dodgy switch contacts after a few years. A shot of Servisol will fix things unless the switches have actually failed (they are usually cheap, poor quality components).

Speakerphones usually do have a electret mic somewhere which is activated when the speakerphone mode is activated and you replace the handset. You should be able to dial out or answer incoming calls with the handset down if you press the speakerphone button, though the exact operational details vary.
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Old 12th Jul 2018, 11:54 am   #18
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Arrow Re: Info. on 'phone requested

"Dodgy switch contacts": yes, we've all been there, haven't we? Whether it's switch contacts, plugs & sockets, edge connectors, valve sockets . . . even solder joints - it's so often the case of mechanical faults (usually intermittent) causing so many head-scratching problems in electronic assemblies.

I get back to this 'phone soon. A number of other things are demanding my attention right now.

Al.
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Old 13th Jul 2018, 8:41 pm   #19
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Default Re: Info. on 'phone requested

If it is a feature phone, it may have four wires. Typically on our mini-switches such as Panansonics the feature phone has extra functionality and works on four wires. The rest of the extensions are commonly two wire working but I believe they can be configured to either two or four wire working in the switch. The majority of our networks are plain old two wire working, and I personally don't have a lot of experience of four wire feature phones except I believe there may be one data pair and power on the other?
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Old 13th Jul 2018, 10:15 pm   #20
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Default Re: Info. on 'phone requested

I know what you mean, I used to maintain hybrid phone systems like the Panasonic "A" series, but the OP has had this phone working on a POTs line albeit unreliably, so it isn't a system phone, it's a regular POTs phone with speaker (maybe full handsfree), one-touch speeddials features etc. so it can reasonably be called a "feature phone".
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