Piezo sounder failing after a few years...

[Pamela]

I have a wireless doorbell with five mains-powered sounders. The
sounder has four volume settings selected by repeatedly pressing a
button.

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime. It happened to
more than one, in different room environments and with all are set to the
same chime, so I guess this is a feature of the piezo component.

Is there some decay process in a piezo sounder as time goes by which
makes it unresponsive to larger currents/voltages used to make it play
loudly?

 

[Mike]

In article <XnsAE1AC14CBEA7C37B93@144.76.35.252>,
Pamela <pamela.private.mailbox@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.
--
--------------------------------------+------------------------------------
Mike Brown: mjb[-at-]signal11.org.uk | http://www.signal11.org.uk

 

[Pamela]

On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14CBEA7C37B93@144.76.35.252>,
Pamela <pamela.private.mailbox@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.

 

[Rich S]

On Sunday, January 9, 2022 at 7:00:13 PM UTC, Pamela wrote:

I have a wireless doorbell with five mains-powered sounders. The
sounder has four volume settings selected by repeatedly pressing a
button.

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime. It happened to
more than one, in different room environments and with all are set to the
same chime, so I guess this is a feature of the piezo component.

Is there some decay process in a piezo sounder as time goes by which
makes it unresponsive to larger currents/voltages used to make it play
loudly?

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...
https://www.digikey.com/en/products/filter/alarms-buzzers-and-sirens/157

-RS

 

[Rich S]

On Sunday, January 9, 2022 at 10:36:44 PM UTC, Pamela wrote:

On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>,
Pamela <pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.

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).

 

[whit3rd]

On Sunday, January 9, 2022 at 11:00:13 AM UTC-8, Pamela wrote:

I have a wireless doorbell ...

Is there some decay process in a piezo sounder as time goes by which
makes it unresponsive to larger currents/voltages used to make it play
loudly?

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.

 

[Jasen Betts]

On 2022-01-09, Pamela <pamela.private.mailbox@gmail.com> wrote:

On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14CBEA7C37B93@144.76.35.252>,
Pamela <pamela.private.mailbox@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.

it could be bad capacitors in the power supply.

--
Jasen.

 

[Chris Jones]

On 10/01/2022 06:00, Pamela wrote:

I have a wireless doorbell with five mains-powered sounders. The
sounder has four volume settings selected by repeatedly pressing a
button.

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime. It happened to
more than one, in different room environments and with all are set to the
same chime, so I guess this is a feature of the piezo component.

Is there some decay process in a piezo sounder as time goes by which
makes it unresponsive to larger currents/voltages used to make it play
loudly?

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.

 

[Rich S]

On Monday, January 10, 2022 at 6:30:55 AM UTC, Jasen Betts wrote:

On 2022-01-09, Pamela <pamela.priv...@gmail.com> wrote:
On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>,
Pamela <pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.
it could be bad capacitors in the power supply.

--
Jasen.

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

 

[Pamela]

On 15:44 10 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 6:30:55 AM UTC, Jasen Betts wrote:
On 2022-01-09, Pamela <pamela.priv...@gmail.com> wrote:
On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>,
Pamela <pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at
the loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.
it could be bad capacitors in the power supply.

--
Jasen.

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.

https://www.youtube.com/watch?v=82fYKP_5DBQ

 

[Robert Roland]

On Sun, 09 Jan 2022 19:00:07 GMT, Pamela
<pamela.private.mailbox@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at the
loudest setting. It\'s a sort of strangled-sounding chime.

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.
--
RoRo

 

[Rich S]

On Monday, January 10, 2022 at 4:53:17 PM UTC, Pamela wrote:

On 15:44 10 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 6:30:55 AM UTC, Jasen Betts wrote:
On 2022-01-09, Pamela <pamela.priv...@gmail.com> wrote:
On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>,
Pamela <pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound at
the loudest setting. It\'s a sort of strangled-sounding chime.

Is there some decay process in a piezo sounder as time goes by

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.
it could be bad capacitors in the power supply.

--
Jasen.

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.

https://www.youtube.com/watch?v=82fYKP_5DBQ

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

 

[Pamela]

On 21:52 15 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 4:53:17 PM UTC, Pamela wrote:
On 15:44 10 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 6:30:55 AM UTC, Jasen Betts wrote:
On 2022-01-09, Pamela <pamela.priv...@gmail.com> wrote:
On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>, Pamela
pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound
at the loudest setting. It\'s a sort of strangled-sounding
chime.

Is there some decay process in a piezo sounder as time goes by

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.
it could be bad capacitors in the power supply.

-- Jasen.

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.

https://www.youtube.com/watch?v=82fYKP_5DBQ

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

You\'re right, it has a small speaker not a piezo sounder! However
wouldn\'t it be even more unlikely a speaker had started to fail than a
piezo transducer? Perhaps it\'s due to a capacitor, as \"whit3rd\" and Jasen
suggested?

This fault occurred in 2 or 3 units in different rooms. Usage has
been extremely low (3 times a week) since the units were bought about
five years ago.

These photos show the speaker and the circuit board.

https://postimg.cc/94sdRZDg
https://postimg.cc/LJXLxNf0

Max volume setting gives trouble (the sound is \"strangled\" and cuts off
after half a second) but one volume step down gives an okay sound,
which means I\'m not inclined to swap out components one by one to track
down the culprit unless there is a very obvious one to change.

 

[Jan Panteltje]

On a sunny day (Sun, 16 Jan 2022 10:23:52 GMT) it happened Pamela
<pamela.private.mailbox@gmail.com> wrote in
<XnsAE2169C6351BB37B93@144.76.35.252>:

On 21:52 15 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 4:53:17 PM UTC, Pamela wrote:
On 15:44 10 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 6:30:55 AM UTC, Jasen Betts wrote:
On 2022-01-09, Pamela <pamela.priv...@gmail.com> wrote:
On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>, Pamela
pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound
at the loudest setting. It\'s a sort of strangled-sounding
chime.

Is there some decay process in a piezo sounder as time goes by

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.
it could be bad capacitors in the power supply.

-- Jasen.

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.

https://www.youtube.com/watch?v=82fYKP_5DBQ

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

You\'re right, it has a small speaker not a piezo sounder! However
wouldn\'t it be even more unlikely a speaker had started to fail than a
piezo transducer? Perhaps it\'s due to a capacitor, as \"whit3rd\" and Jasen
suggested?

This fault occurred in 2 or 3 units in different rooms. Usage has
been extremely low (3 times a week) since the units were bought about
five years ago.

These photos show the speaker and the circuit board.

https://postimg.cc/94sdRZDg
https://postimg.cc/LJXLxNf0

Max volume setting gives trouble (the sound is \"strangled\" and cuts off
after half a second) but one volume step down gives an okay sound,
which means I\'m not inclined to swap out components one by one to track
down the culprit unless there is a very obvious one to change.

Also check the soldering, resistor on side looks like a bad joint?
Just re-solder everything.

 

[piglet]

On 16/01/2022 10:23 am, Pamela wrote:

On 21:52 15 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 4:53:17 PM UTC, Pamela wrote:
On 15:44 10 Jan 2022, Rich S said:

On Monday, January 10, 2022 at 6:30:55 AM UTC, Jasen Betts wrote:
On 2022-01-09, Pamela <pamela.priv...@gmail.com> wrote:
On 21:37 9 Jan 2022, Mike said:

In article <XnsAE1AC14...@144.76.35.252>, Pamela
pamela.priv...@gmail.com> wrote:

Several of the sounders now struggle to make much of a sound
at the loudest setting. It\'s a sort of strangled-sounding
chime.

Is there some decay process in a piezo sounder as time goes by

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.
it could be bad capacitors in the power supply.

-- Jasen.

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.

https://www.youtube.com/watch?v=82fYKP_5DBQ

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

You\'re right, it has a small speaker not a piezo sounder! However
wouldn\'t it be even more unlikely a speaker had started to fail than a
piezo transducer? Perhaps it\'s due to a capacitor, as \"whit3rd\" and Jasen
suggested?

This fault occurred in 2 or 3 units in different rooms. Usage has
been extremely low (3 times a week) since the units were bought about
five years ago.

These photos show the speaker and the circuit board.

https://postimg.cc/94sdRZDg
https://postimg.cc/LJXLxNf0

Max volume setting gives trouble (the sound is \"strangled\" and cuts off
after half a second) but one volume step down gives an okay sound,
which means I\'m not inclined to swap out components one by one to track
down the culprit unless there is a very obvious one to change.

It could well be a capacitor fault. However I think an electrolytic
(like C1 or C3) drying out while possible is unlikely to affect two
units in the same house at similar times, it is too much of a coincidence.

My suspicion is the 630V film dropper cap (big red cap on the right
below the push buttons). Mains overvoltage spikes, as generated by
appliances bwing switched off, can destroy sections of metalization and
reduce the capacitance. The affect of this is to reduce the power supply
current capability so the internal supply sags under high load. The
lower volume settings are suppported but at high volume the bulk filter
electrolytic soon runs out of charge and the volume fades to lower level?

Multiple units in the same household could be expected to experience the
same degrading mains spikes at the same moments. Can you measure those
caps and see if their value has fallen significantly?

piglet

 

[Bill Beaty]

On Monday, January 10, 2022 at 3:35:29 AM UTC-8, Chris Jones wrote:

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

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?)

..

 

[Phil Allison]

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

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

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?)

** Ag2S is a good *insulator*.

Stops relay contacts working.


....... Phil