Vintage 706L not ringing

[russell_w_b]

Originally Posted by Daisy May

I have an old multimeter (ie not digital ) and can use it under instruction. Ive already tested ohms to show that ringer is good. What next?

Set your multimeter to measure a.c. Volts, then measure across Terminals T4 and T16 when the telephone is meant to be ringing - with the handset 'on-hook'. You're looking for about 75V across these terminals, to which your bell is connected. An analogue multimeter like yours is probably better than a digital one under the circumstances, as the ringing cadence is only 400ms on, 200ms off, then 400ms on again (repeated until answered), so watch for a peak on your meter pointer.

If you get about 75V a.c. here, then your problem is between these terminals and the bell coils.

If you measure no voltage here, it's possibly a break in the capacitor track on the PCB.

[Daisy May]

Russell - ok so I worked out that I should be dialing in to check what's going on and I did get 75v and it was swinging around as it rang, back and for.

So the problem is as you identified.... something to do with the pale pink leads, T4 and T16 that seem fairly inaccessible at the moment!

[Daisy May]

but maybe I'll pluck up courage and follow Sam Hallas 'take a phone to bits' website?

[Dave Moll]

With the 'phone NOT connected to the line, I assume then that you get an open-circuit reading between T4 and T16. If so, you need to check the reading on each link in the circuit (T4 to other end of wire at bell coil, I take it you've already got the correct reading across the bell coils, then other end of coils to T16 - there must be a discontinuity somewhere.

If T4 to T16 is OK, as Russell says, the capacitor or its wiring is the problem area. To check the tracks between T7 and T9 and the capacitor itself, you will need to remove the circuit board (held in place by two screws). I assume your meter doesn't include a capacitance range - in which case you may be able to do a quick-and-dirty check on resistance and look for a brief blip on the meter to indicate the capacitor charged up.

[TonyDuell]

With the telephone unplugged, set your multimeter to a resistance range that covers 1KOhms (probably marked 'Ohms * 100' or 'Ohms * 1K' on the selector dial). Put one probe on T4 and the other on T16. What resistance do you measure? Does the meter needle move at all?

The 2 bell coils are connected in series. One pink wire goes to one end of one of the coils. There is a connection from the other end of that coil to one end of the other coil. And the final end of 'the other coil' goes to the other pink wire.

I seem to remember there are 2 versions of the Telephone 706 Mk2. In one of them the connection between the coils is made by a wire connected to the coils. In the other, it's made by having one tag from each coil soldered to the circuit board, there is a copper track on the board that links them.

The 706 Mk2 is actually one of the easiest telephones to take apart, and a good 'first project' as a result. It's some time since I've done one, but I think you can loosen (not totally remove) the short screw at the top of the dial mounting (you put the screwdriver in from the side of the telephone) and then unhook the complete dial unit. It's still connected to the circuit board by 5 wires. Then one (? maybe 2) screws come out and the entire circuit board assembly lifts out leaving just the bell gongs attacted to the baseplate of the telephone.

[Daisy May]

thanks for this - think I'll need a strong cup of tea before I start this bit!

[Daisy May]

if I'm reading the right part of the gauge - its reading 2.2 (on the top line), is that the right one?

[Daisy May]

Looks like the coils are soldered to the board on mine - its a 706L - AEG 66/ 2A.

[russell_w_b]

Originally Posted by Daisy May

if I'm reading the right part of the gauge - its reading 2.2 (on the top line), is that the right one?

It depends on your meter! Have you shorted the leads together to set it to read zero Ohms before starting? What sort of meter is it? Any chance of a photo?

The handset should be 'on hook', ie: sitting on the cradle when you measure the resistance of the bell coils at Terminals 4 - 16, so you don't include the regulator and receiver circuit in parallel with it. You should be looking for a reading of about 1000 Ohms on your multimeter.

[TonyDuell]

It is probably simpler to remove the screws that hold those pink wires from the bell coils in place and move the wires away from T4 and T16. Then connect the multimeter (Resistance range as before) between the 2 pink wires, one probe to each wire.

What reading do you get like that?

[russell_w_b]

Originally Posted by TonyDuell

It is probably simpler to remove the screws that hold those pink wires from the bell coils in place and move the wires away from T4 and T16.

Good idea. But the 706 has a 'hold-down' lever so you can work on the instrument and simulate it being 'on-hook' when in any position without having to balance the handset on the caseless cradle switches and see it fall off all the time.

If you look at the photo of my Phoenix-manufactured 706 Mk: II, you can see the lever. My finger is pressing down on the cradle switch and my thumb is about to press the fat bit of the lever so the top of aforementioned lever will spring out and hold the cradle switch in the 'on-hook' position.

[TonyDuell]

Sure. And you release the 'hold down' by pressing and releasing the handset rest plungers.

For the record, there's also a catch, of a rather different design, in the Telephone 746.

[dagskarlsen]

The use of an old meter may actually be better than a digital, but it may be hard to measure a capacitor. When you have the phone connected to the line, but not ringing, and the hoock-switch pressed down (on hook) you should read the same DC voltage as across the line, when you go off hook the voltage should drop slower than if you measure across the line, when you go on-hook again the voltage should raise slower than across the line. If so, the capacitor is probably OK.

The ringer may have a bad coil, if so the capacitor test will probably not work as described. The ringer may also move with to high mechanical. resistance it should move just by shaking the phone.

[Daisy May]

no reading. Ill try and include a photo of my old meter...

[Daisy May]

sorry its telling me my files invalid again....

[Cobaltblue]

Originally Posted by Daisy May

sorry its telling me my files invalid again....

Are you using the information Graham linked in post #13 ?

Cheers

Mike T

[AndiiT]

Hi, Looking at the picture of your wiring, it's difficult to see where the connections to the auxiliary (Press) button are connected, it's possible that they may be (incorrectly) wired to short out the bell motor which would cause no incoming ring. I would start by disconnecting the wires from the auxiliary switch and parking their tags on spare terminals T11, 12 and 13, you don't need the switch for the phone to work correctly anyhow.

Then initially wire the phone for "two wire working" as follows -

Link T4-T5-T6-T7

Link T8-T9

Link T16-T17-T18-T19

Red of line cord to T8
White of Line Cord to T18

Blue and Green of the line cord can be parked on T14 and T15 for now.

If your phone still doesn't ring on an incoming call, you will then need to look for a fault within the instrument, such as an open circuit bell motor or a faulty switch hook.

If the phone does ring when wired as a two wire device, you can then try connecting as a "three-wire" device as follows -

Link T4-T5-T6

The link at T8-T9 can be either left in place or removed

Link T16-T17-T18-T19

Red of line cord to T8
White of line cord to T18
Blue of line cord to T5
Green of line cord to T15

If the phone then does not ring, you have either a problem with your master socket or extension wiring (if fitted)

Regards

Andrew

[dagskarlsen]

]It is a little bit more struggle to take it down to the basic way of testing, but its hard to fail. The clue is to have some 9V batteries of the pictured size. (Reason: high internal resistance compared to most other power sources)
1 battery between Red and whit, and the phone should work in hence of going off hook and hear yourselves. If you take 3 batteries in series as pictured, the 27V should be enough to move the clapper fort or back depending on polarity.

2 wires from terminals for ringer-motor Ø4 and Ø16 that are touching the batteries + and then changed forth and back should make the clapper move. If it moves, but not hitting the gongs, the gongs should be turned to the clapper hit it, but not are resting in touch with it.

[Daisy May]

Thank you so much to all the telephone experts who have offered advice and guidance. I've tried nearly everything you've suggested and I have learnt a lot. In this case, I've learnt that some things are beyond me and I am abandoning my 706 ringing problem. I'll be donating it to our local antique centre where someone else can carry on the good work.

Once again, thank you to everyone !!

[Dave Moll]

That's a shame! It's a pity I don't live near enough to give it a look-over, as I'm sure it can be sorted. Maybe someone else on the forum does.