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Old 14th Apr 2012, 9:17 pm   #1
jonboysez
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Default Trouble with a 706 faint dial tone.

Hi,

I've acquired a 706 that needed rewiring so I've wired it according to the instructions on the relevant sites and noticed that the dial tone was very faint and when phoning out neither I nor the receiver could hardly hear each other talking. I tested the bell by phoning it from my mobile and it worked ok, sometimes needed me to nudge the clapper to get it going, but usually worked ok.

I have been known to get the wires reversed so I reversed the wiring and this time the dial tone was strong and both speech sent and received was strong, but now the bell stopped ringing on incoming call, so I reversed blue and green wires but this still did not make the bell ring.

I've tried the wires in different combinations that many times now, but always white and red to either T8 and T18, and blue and green to either T6 and T15). I did a bit of research and noticed the regulator board seems a bit slack in the slots, so took it out gave the pins a clean and pushed it back in but its still a bit wobbly in the slots, I've turned it over to see if that makes a difference too but I'm still left with the same problem - either I have strong dial tone and no ringing bell, or faint dial tone and a ringing bell!

The original line cord that came with it only has 3 inner wires - white red and green (I forgot to see how it was connected begore disconnecting it - silly me!) but I think I found the original wiring online and tried it - bell rung but faint dial tone again - I've also swapped the transmitter and receiver in the handset - does it matter which way round the wires go at either end?

I'm also using non-standard line cord (it's American 4 wire flat telephone cable - yellow, green, red, black in place of white green blue red - got a good deal on it). The handset is correctly wired inside the telephone. I've disconnected rectifier 205 and replaced 3.3k resistor with strap until I sort it, if ever!
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Old 14th Apr 2012, 10:38 pm   #2
OscarFoxtrot
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Default Re: Trouble with a 706 faint dial tone...........

The symptoms and the non-standard line cord both suggest that the problem is with your connections to the phone line on pins 2,3 and 5 of a BT line jack socket. Go back to the diagrams and check the socket-to-phone numbering and ignore the US wiring colour scheme.
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Old 14th Apr 2012, 11:51 pm   #3
ajs_derby
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Default Re: Trouble with a 706 faint dial tone.

What OF said. Forget colours in the line cord, go by terminal numbers.
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Old 15th Apr 2012, 9:26 am   #4
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

No - I have made a direct substitution for the US coloured wires to the UK wires i.e. my yellow wire is the UK white wire, my black wire is the red UK wire etc (in my explanation I have used the UK colours but substituted them with the US colours in my line cord). The type of wire can have no bearing on it can it? i.e. I assume different thickness of wire will have different resistance?
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Old 15th Apr 2012, 9:34 am   #5
Nickthedentist
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Default Re: Trouble with a 706 faint dial tone.

No, even the thinnest wire should work.

I would check and double check your wiring codes. The line cord wire that goes to terminal 2 of the socket is traditionally RED,
3 - BLUE and
5 - WHITE.

Note that the numbered terminals to which I refer are the screw or IDC terminals where the house wiring attaches to the socket.

Confusingly, some sockets also have numbers printed on the PCB where the socket itself is soldered on, and these are reversed (some bizarre British Standard numbering as opposed to BT's own numbering system, I believe)

See my scrappy drawing here: http://www.vintage-radio.net/forum/a...2&d=1206469276

Then, use one of the recommended "conversion" methods for wiring the phone, you shouldn't need to invent your own!

If this still fails, try the phone on someone else's socket. It could be that yours is miswired.


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Old 15th Apr 2012, 9:45 am   #6
russell_w_b
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Default Re: Trouble with a 706 faint dial tone.

Have you undertaken fundamental continuity checks on the plug and lead?

Have you tried a similar telephone on the socket you are trying your 706 on?

Don't get hung up on core colours or size of conductors. It's a telephone, not the National Grid. Connect your standard BT plug to your telephone as follows:

Looking at your BT plug with the pins uppermost and away from you... )Note: pins 1 and 6 aren't used).

Pin 2 connects to terminals 16, 17, 18, 19.
Pin 5 connects to terminal 8.
Pin 4 connects to terminals 5 and 6.
Remove the link between terminals 4 and 5 and replace it with a 3K or 3k3 resistor. Note that this isn't essential if it's the only instrument on the line! But 4 and 5 need to be connected either by link or by resistor.
Remove links between terminals 6 and 7 or 8 and 9, or both, if you wish.

Note also that pin 2 of the plug mates with terminal 5 of the socket rear connection; pin 4 with socket terminal 3, and pin 5 with socket terminal 2. If your socket is wired correctly you needn't worry about this. Just get your plug connections correct WRT the telephone terminals.
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Old 15th Apr 2012, 10:24 am   #7
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

Yes I've used multimeter and tested and retested the continuity of the line cord and the handset cord - changed the BT plug and one of the spades. I've also tried another 706 in the socket and its fine - I took the lid off that and its wired identical to the other with the fault - I am convinced that I originally had the wiring correct, but swopped around just to see. I will take a line cord off a phone that definitely works (with the proper UK wires) and try that, altho I'm 99% certain it won't make a scrap of difference. I'm wondering if the bell mechanism is on its way out or the dial or switches are faulty?
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Old 15th Apr 2012, 10:38 am   #8
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

I have wired it up exactly like this picture except my phone has the brown wire from the dial attached to T3 (if I remember rightly), and not D3 as the early phones were wired.
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Old 15th Apr 2012, 11:03 am   #9
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

Just to eliminate the US wire problem - BT 4 pin plug, with pins 2,3,4,5 and clip on right as I look down at it - yellow, green, red, black, clip - then inside phone - yellow to T18, black to T8, red to T6, and green to T15 - is this correct? The extension socket I'm plugging it into has been used by loads of my phones with no problems so that must be ok. It gives a strong dial tone with yellow and black swopped over inside the phone for some reason.
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Old 15th Apr 2012, 11:17 am   #10
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Default Re: Trouble with a 706 faint dial tone.

The wiring in your pic looks spot-on to me (though the T8-T9 strap isn't needed).

The bell should be fine, and I note that it's a later 2x2K one. A tiny drop of oil on the two bearings wouldn't go amiss, and you should adjust the gongs so that the clapper is just clear of each gong when the armature is in either of its rest positions.

I would swap the regulator, transmitter, receiver and dial, one by one, with the working 706, to establish if they're at fault.

I also see that you have the PCB (rather than hard wired) variant. These can sometimes suffer from tiny hairline cracks if the phone's been dropped. Hard to find, easy to repair at least.

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Old 15th Apr 2012, 12:34 pm   #11
russell_w_b
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Default Re: Trouble with a 706 faint dial tone.

Can you try these two things?

1): Strap T10 to T8 (the dial pulse contacts) to see if that makes a difference?

2): Strap T10 and T3 (the mic) similarly.

Also: reverse your regulator so it is shorted out, to eliminate it.
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Old 15th Apr 2012, 6:26 pm   #12
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

I've tried everything now.
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Old 15th Apr 2012, 6:29 pm   #13
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Default Re: Trouble with a 706 faint dial tone.

Quote:
I've tried everything...
What, ALL the things that Russell and I said in posts 10 and 11
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Old 15th Apr 2012, 6:36 pm   #14
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

I swopped the handset and regulator from working 706, tried a different line cord, and tried the 2 straps as mentioned in last but one post all to no avail. I have noticed that I can't hear a dial tone at all now with the regulator in the normal position, and a very faint dial tone with it upside down - I'm wondering if it's the contacts that the regulator fits into that are not connecting somehow or maybe a crack somewhere.
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Old 15th Apr 2012, 7:12 pm   #15
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Default Re: Trouble with a 706 faint dial tone.

Did you try a different dial? Only 5 screws though you need a nice small screwdriver and musn't apply too much pressure.

If still no luck, a cracked track is the likely suspect. Do plenty of "cold" checks with a resistance meter, including from components on the main PCB to components on the regulator, to check for poor contacts between the two too. And have a good look with a really strong light. Brush the PCB clean with a stiff brush first.

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Old 15th Apr 2012, 7:32 pm   #16
jonboysez
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Default Re: Trouble with a 706 faint dial tone.

I'm going to leave it for a while, doing my head in now, never had this much trouble with any other phone - I am ok doing continuity checks of cables with my multimeter, but testing circuit boards is a bit beyond me at the moment - I hate being beaten but I know my limitations! I haven't swopped the dial - was hoping not to have to do this, although I have done it before, just not full of confidence now that it will make any difference for all that effort!
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Old 15th Apr 2012, 7:39 pm   #17
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Default Re: Trouble with a 706 faint dial tone.

If you disconnect your dial (not difficult - make a note or take a pic of the wires before starting), and connect terminals T8 and T10 together, you'll have the equivalent of a dial-less CB (central battery) telephone. By doing this, you'll eliminate any inadvertent dial-off normal contact shunts or H/R pulse contacts at a stroke.

Re-connect the dial when you get it sorted.
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Old 17th Apr 2012, 4:23 pm   #18
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Default Re: Trouble with a 706 faint dial tone.

What is confusing here is that there may be a little crack in a PCB track. If visual inspection fails each track will have to be measured with a low ohms range from point to point as the cracks often appear at the edge of the solder pad between the copper and the soldered copper and are hard to see.
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Old 21st Apr 2012, 9:45 am   #19
mike_newcomb
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Default Re: Trouble with a 706 faint dial tone.

Hi Jonboy,

I think you may have gone too deep trying to correct the problem, and your efforts may now be causing further problems. Go for the simple things first.

You first advised it need re-wiring - why, what and where exactly did you mean by this.

From memory, the straps settings were quite varied on this phone, depending on where installed and/or whether it was a master or slave. Possibly it was used in a location where the strap settings would stop it working correctly in yours.

The picture you provided was good - can anyone else here provide the same picture of a 706 that is working correctly?

When testing I suggest using the master socket, as a slave may compound an issues. Also if broadband is installed may have a bearing.
e.g. I recently had a problem with a broadband splitter where the phone socket was physically missing 2 pins, such that phones with UK ring wiring would not ring.
Also if the phone should be strapped as a master.
Good Luck - Mike
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Old 21st Apr 2012, 10:42 am   #20
Dave Moll
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Default Re: Trouble with a 706 faint dial tone.

I have to say that my experience with ADSL splitters is the opposite of Mike's in that they include a ringing capacitor that ensures that a three-wired 'phone rings (and that its receiver functions correctly) - in fact, I have some that I use specifically for this purpose on sockets that aren't wired for three-wire equipment.
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