Activating HKC Sounder on Bench

[Eugene's DIY Den]

I've taken my sounder off the wall and I'm checking it on my workbench. It's powered from a desk power supply set to 12 V, connected to the external bell input terminals. I would have thought it would activate with the back tamper open, but it didn't. I closed the back tamper for 4 seconds and opened it and it still didn't activate and tried the same with the battery connected. Shouldn't all of these tamper conditions and also open circuit holds activate the unit? If a burglar cuts the cable, shouldn't the 6 V battery activate it, or is it only edge triggered (i.e when the tampers were initially closed when the sounder was powered down and then opened that triggers it? ) In this case, how can I generate a false alarm? Which terminals do I need to connect?

Edited April 22 by Eugene's DIY Den

[Eugene's DIY Den]

I'm thinking I need to connect 0V from the power supply to SAB Hold, because that's actually the negative power supply to the sounder. Then connect 0 V to to External Bell -, because that seems to be Trig - on the schematic.

[Eugene's DIY Den]

23 hours ago, Eugene's DIY Den said:

I'm thinking I need to connect 0V from the power supply to SAB Hold, because that's actually the negative power supply to the sounder. Then connect 0 V to to External Bell -, because that seems to be Trig - on the schematic.

Yes, that worked. The next thing is to open the transducer to see if anything can be fixed, probably not. Also I'll put a scope on the sounder output on the board to see what has happened. A cheap meter shows 77 V instead of 120 V, but that's possibly because the meter has a limited bandwidth. Alternatively one of the drive transistors/MOSFETS  may have blown.

Edited April 23 by Eugene's DIY Den

[james.wilson]

The piezo side is quite high voltage id be cautious. Just get a new one

[Eugene's DIY Den]

21 hours ago, james.wilson said:

The piezo side is quite high voltage id be cautious. Just get a new one

 

120 V AC. Presumably that's RMS , because peak voltage is nearly 250 to 300 V. This is the waveform on a scope.

Anyway I had a stroke of luck. My old sounder has the exact same piezo transducer so I'm going to use that. Hopefully it's the same voltage, but it looks totally identical. The HKC sounder is taking nearly 200 mA when sounding after I replaced the piezo element, which tallies with the 250 mA peak they give in the spec. Also the 6 V battery is still working fine. After 15 mins of alarming, voltage  fell to 5.75 V.

 

 

Edited April 24 by Eugene's DIY Den

[al-yeti]

1 minute ago, Eugene's DIY Den said:

120 V. Presumably that's RMS , because peak voltage is nearly 250 to 300 V. This is the waveform on a scope.

Anyway I had a stroke of luck. My old sounder has the exact same piezo transducer so I'm going to use that. Hopefully it's the same voltage, but it looks totally identical. The HKC sounder is taking nearly 200 mA when sounding after I replaced the piezo element, which tallies with the 250 mA peak they give in the spec.

Didn't realise it was old bell , bin it now 

[Eugene's DIY Den]

6 minutes ago, al-yeti said:

Didn't realise it was old bell , bin it now 

 

That's the one I salvaged the piezo element from, which is working fine now in the HKC one. So does anyone know whether 120 V AC is a standard voltage for these?

Edited April 24 by Eugene's DIY Den

[MrHappy]

pizeo's vibrate,

 

thrips / thunder bugs or whatever climb inside stuff & don;t vibrate no more...

[Eugene's DIY Den]

1 minute ago, MrHappy said:

pizeo's vibrate,

 

thrips / thunder bugs or whatever climb inside stuff & don;t vibrate no more...

I thought something like that may have caused it. Blew the plastic horn out with an air compressor, but it didn't make any difference. There was some corrosion around where the leads were soldered onto the element (it's just a flat disc with a metal plate on one side and a metal coating on the other). Cleaning that didn't do anything either. So I reckon the crystal just cracks and can't vibrate properly.