Piezo sounder failing after a few years

Over the last 20-odd years, I've had a number of landline/wired phones with electronic/piezo ringers do exactly that. You can sort of hear them ringing, but barely. Then they just stop altogether.

Three different brands of handset, two of each, ... yet two plug-in ring-repeaters (piezo and LED flash) have happily worked to fill in for the missing sound, and they date back from the early 80's and are still going.

My door bell alarms sound alright at lower volume settings but on the loudest setting it makes a strangled sound for less than half a second then stops.

It's almost as if the piezo sounder is so overloaded it can't make a proper sound.

My first suspect : the sound-emitting transducer, a.k.a. "buzzer", inside the remote sounder. Since you mention it is a "piezoelectric" type.

A piezo crystal can fail (if over-driven - due to poor design, trying to get it to emit as loud as possible; or is subjected to wide temperature swings; or just poor manufacturing.) Once cracked, parts of it may still response to a drive signal, but just not the whole piezo crystal. This weakens the sound- output very noticeably. The DC-powered buzzer includes its own drive circuitry, to help set the drive signal to and output to the best frequency and level.

To fix Your devices, I would need to know a little more about them. There are many buzzers types...

-RS

OK, given that it CAN produce a clean sound, at lower volume, then it could also be circuitry (or the external power supply, it if uses one).

Yeah, there's a couple of mechanisms. Most ubiquitous, is the use of resonant structures with polymers; those polymers can cross-link with age and when they get stiff, the elastic deformation and spring constants change, so the resonance doesn't make the same noise. Speaker surrounds (and re-coning of speakers) is a persistent issue for music reproduction. Less likely, is foreign material; could be dust, dirt, or insect eggs trying to hatch in an out-of-the-way spot.

Clapper-bell-coilspring can last decades, but dirt can stop those, too.

it could be bad capacitors in the power supply.

Often piezo discs have a silver plating for one electrode. I have seen this get quite tarnished over time. If the contact to the silver electrode is soldered I would not expect the tarnish to make any difference, but sometimes they use a spring-loaded contact that just presses onto the electrode. I think in this case, when the tarnish gets thick enough it could stop it from working, though I would not expect it to tarnish much exactly in the spot under the spring-loaded contact where it would be a bit protected. If the contact moved a bit due to vibration, it could get onto a more tarnished part. Perhaps if you open it up, you might be able to see whether this is a pausible explanation for your particular device.

Indeed. Or one of the diodes in the bridge rectifier, opened up, so either way, the DC power supply rail has high(er) ripple and higher impedance. (When demanded to produce higher volume, the power supply must supply higher current. The DC voltage sags / drops, in this instance.) I assume this is a cheap consumer product without voltage regulation....

=RS

The actual model is Tecknet WA638 wireless door bell.

I want to make sure any replacement I buy doesn't suffer the same fate after a few years of extremely light use.

For background, someone is demonstrating it in this video. At 3m45s she shows the different volumes and mine initially sounded just well.

Check if the piezo elements have simply come un-glued from the plastic case.

I saw this on a simple PIR controlled burglar alarm once. The sound went from unbearably loud to very faint. Once glued back down, the sound was perfectly unbearable again.

Thanks for posting that video. The various sounds and relatively "good" fidelity seem much better than what a piezo transducer could produce, IMHO. I think its more likely to be a dynamic (voice coil) speaker. Have you had the chance to open up the receiver unit, and take a look? Post a pic? Dynamic speakers can break, if grossly overdriven (or poorly made). But I still suspect the circuitry.

If your comfortable working on a live unit, opened up, then plug your receiver via extension cord, and examine the speaker. Could try wiring in a substitute known-good speaker, to see if the sound quality improves. Next, carefully, with a DVM, probe the power supply DC voltage. See if the DC reading drops by, say, over

20%, when the unit is emitting a (loud) sound. Repeat, with DVM set to AC volts; the AC reading should be minimal or zero, even when producing a sound. If the reading jumps to, several volts, then either a rectifier diode or the filter capacitor is bad.

= RS

check

Sillverrrrrrr. Pricey! It only needs to be thick at the solder-dot. Perhaps the latest mass-production technique is to reduce the sliver to a few molecules thickness. Then, after a few years, it's ALL tarnish. (silver sulfide, is that a resistor?)

.

Bill Beaty wrote: ================

** Ag2S is a good *insulator*.

Stops relay contacts working.

...... Phil