Old door bell - electric?

[rarara]

Hi, have a push button door bell (old - victorian) which no longer works after stripping wallpaper and presumably damaging it. It looks like the self-interrupting type with an electronagnet (similar to pics that I have found online) but that would suggest its connected to the mains, right?

I took it off the wall to have a look and neither of the two wires showed any current (using my small light-up electrical screwdriver!), nor did any of the two wires at the outside button.

This leads to a few questions:

1) Can this type run purely on the strength of a magnet and without any mains current?

2) If it is connected to the mains supply, would it be stepped-down to such a degree so the screwdriver tester wouldn't light?

3) There is an old green metal box marked GEC near the consumer unit that I always thought obsolete - is this likely to be connected to the bell? Searching some threads made me think of this. Could this somehow have become faulty?

I can try and get some pics when I get home, but some general advice would be appreciated

 

[bernardgreen]

If the bell has been working for years and you have never found or had to replace a battery then it is powered from the mains via a transformer.

The green box is probably the transformer, it will have mains supplied to one side and the output will be a very low voltage most likely 8 or 12 volts. This will feed the bell via the bell push on the door.

If the tranformer feels a bit warm then the mains is still there and the fault is in the 12 volt circuit.

"Light up" screwdrivers need at least 100 volts to light up. They can give false readings that something is safe to touch ( no light ) when in fact the item is live and dangerous so throw the screwdriver away and instead use a multimeter.

 

[rarara]

OK, have used the multimeter and get a reading at the button outside, but nothing at the bell itself. Here is the bell:

Untitled

• rarara
• 10 Sep 2012
• 1

And here is (I think!) the transformer which is possibly very slightly warm:

Untitled

• rarara
• 10 Sep 2012
• 1

How does the transformer open? Will I really need to replace the wire leading from this to the bell/button as does it seem this might have got damaged?

 

[TicklyT]

Do you see any power reaching the bell when the bellpush is pressed?

(If there was a constant power supply to the bell, it would ring constantly)

Oxidation, maladjustment or excessive pitting of the interrupter contacts can stop the bell operating.

Some bells are adjusted by turning the bell gong, which has it's fixing screw slightly off centre. If the gong gets turned round too far, it can jam the mechanism.

 

[rarara]

no multimeter reading at the bell with the button held. what would the next step be - do i need to replace the wire completely?

 

[bernardgreen]

It appears that there is just a single cable (2 wires) to the bell and a single cable to the transformer. If there is only a single cable to the bell push then somewhere these three cables meet and interconnect. Very often this joint is made by twisting the wires together and any disturbance during decorating can break the joints.

 

[rarara]

i believe so - there was a connection like that which got disturbed during redecoration. maybe a good time to rewire it, as i'd like to keep the old components.

any idea how the transformer opens? is there a hinge, as it doesn't appear obvious.