Doorbell puzzle (old school)

Sounds like the doorbell in my parents house. Built in about 1954.

With a DVM, check if power to the button is present. If so, is it AC or DC? If there's no voltage, look for a broken wire.

OK, the button works. Now, check if there's anything on the wires coming from the transformer.

That would be my guess. This was a problem in my parents house and in two ancient rentals I lived in over the years. What happened was the solid copper wires had become corroded by years of rain. Oddly, that also made the wires a little stiff and brittle. Move the wires and they'll break at the nearest "crimp", which would be where the wires were bent into a "ring" and held in place with a brass screw. The break was usually at the base of the bend. The wire strippers, would cut through the cloth insulation and "nick" the wire copper wire. A little bending, and the wires would break.

Felt? Do you have access to a borescope or endoscope, normally used for visually inspecting in tight spaces? I have several and use them quite often. Something like this:

Find a "fox and hound" type signal tracer. I also have several of these (for AC power line and telco):

If you have money to burn, try one of these:

You give up too easily.

My intuition suggests a crude DC power supply either with a very old capacitor or a wire that's getting hot with increased use.

Good luck.

How do you know it's a 12V AC system if you can't find the transformer? Had you checked the voltage some time previously, or had the doorbell failed to work when the AC power had been cut off for some reason? In a previous house we owned there was a door chime run by four "C" cells inside the chime unit. They were there when we moved in and were still working when we left 12 years later! In the new (but older) house I replaced the wired bell which was unreliable as the wire had broken just inside the wall. The wireless bell is much better.

What's inside the chime box you mention below?

Did you use a 12V AC source for the test?

Switch? Did you mean the bellpush contacts?

What voltage do you see across the red wires when tested "as is", and when the bellpush button is pushed?

What happens when you short the bellpush leads with, eg croc clips, rather than use the button? Does the bell ring consistently every time, or is it still intermittent? If it works, try cleaning the bellpush contacts and see if that helps.

Not really...

Not likely, not without tracing wires and finding that transformer. In our last house, someone had wired the front and back door bell to the same chime. I fiddled with the system for hours, until I finally got the rear door bell to "ding-dong". The front doorbell button (same chime) would only "dong". You know what, that was close enough for me!

What country? System differs by country.

Here (Spain) the doorbell is often on mains voltage (230Vac). Mine stopped working few years back. I decided not to try to repair it, because some of the wires are directly embedded in the plaster or mortar and brick wall work outside, instead of the more modern method of embedding plastic tubing.

So I bought a wireless system. The button outside has its own battery; the internal bell is powered by mains. The interconnect via radio.

My neighbour had done the same thing years before me.

Often doorbells can "ding-dong" or just "dong", depending on how you connect the two wires at the bell, like this:

outside terminal {O} middle terminal {O} outside terminal {O}

One outside terminal is "ding-dong", the middle terminal is common and other outside terminal is "dong" only. All you need to do is move the outside wire to the opposite outside terminal, assuming your bell is like that (and working).

Ed

Find the breaker (or fuse) at the panel that disables the doorbell. That breaker *should be* labeled so that you know what circuit it protects. If not labeled you'll have to search to find what's not working. Your doorbell transformer is somewhere on that circuit. The code requires that it is accessible. Accessible means you do not need to remove any permanent part of the building (e.g. wallboard) to get to it. It may be hidden it behind storage boxes etc) Likely places in general: at the breaker panel/near the furnace/in the basement/the garage/attic and similar places.

Your description of the problem suggests the possibility of an intermittent open in the transformer or the bell or the wiring.

Ed

Finding a doorbell transformer in a wall or ceiling is fairly easy. The typical 18 or 24VAC transformer isn't very well shielded.