Piezo Murata PKM25-6AO what is it?

[carpenter]

I have an alarm from DSC, the piezo converter PKM25-6AO takes care of the acoustic signaling in the keyboard.
Unfortunately the keyboard is muted.
After disassembly I found PKM25-6AO. Maybe I'm not picky, but from this datasheet I don't even know what the converter has three outputs for?
I didn't really look at the connections, but one Schmit trigger from MC14584B is connected to the F and M outputs.
I assume that it will be some kind of self-oscillating circuit that oscillates at 6.8kHz.
I will examine it more closely tomorrow, but if anyone has any idea why the inverter has three outputs or how it is excited....
in my opinion both the piezo transducer and the MC14584B should be near-immortal things, but some of it is dead,

 

[carpenter]

Today i had time to research it a bit more.

Pins piezo transducer
G - ground base metal plate
M - main
F - feedback

in parallel with the M and F terminals of the piezo is a shmitr triger and resistor 47k.
The only other component is a diode resting on output number 4 of the 8-bit shift register HEF4094, which apparently determines whether the circuit oscillates 1 or does not oscillate 0 and is silent.
Diode, resistor is OK.
MC14584B is OK
When I apply a 6.8kHz 5V sine wave to the PKM 25-6AO, the piezo sounds beautiful.
Unfortunately all together it's dumb

 

[betwixt]

Two wires are the drive to the resonator, the third is a 'pick-up' wire used to provide feedback so the resonator itself sets the frequency.

Brian.

 

[D.A.(Tony)Stewart]

You could also drive it from a midi audio to audio signal to sound like a Mario game

 

[betwixt]

Just a guess based on everything else checking out OK: the feedback connection has come adrift on the resonator disk. You can check it by injecting your sine wave on the feedback wire, it should still make a noise but probably much quieter. Why 6.8KHz? these things are usually around 2KHz.

If all else fails, you can add some parts around the inverter to make it into a free-standing oscillator.

Brian.

 

[D.A.(Tony)Stewart]

 

[carpenter]

Yes, that's how it occurred to me.
What is not clear to me, why it doesn't work?
More precisely, I do not understand why the manufacturer does not specify the characteristics of the converter
The connection resembles a Pierce oscillator, unfortunately it does not oscillate, even if it oscillates with other external excitation.

 

[D.A.(Tony)Stewart]

What circuit voltages do you get? Almost any piezo will do for a replacement if you have a circuit.

Would U like to measure impedance? or Voltage or resistance?

Simply not enough gain to overcome attenuation.