HP34405A low piezo volume

[Najgel254]

Hello,
I am trying to repair my HP34405A where the piezo buzzer went suddenly low on volume. I can barely heat beeping it when doing continuity test.

I measured all surrounding parts, resistors were okay, all values matched the package marking. Transistor is okay too, i replaced it anyways but with no result. The inductor which is in series with piezo, have value of 360R and inductance 122mH, which seems little bit high for that part, bud when  I replaced it with 10mH one, the result was still same. The supply voltage is 8,9V, then I desoldered piezo and connected it to signal generator with amplitude 8V it was literally screaming so I this the part is okay.

I measured all signals the signal from MCU is present, amplitude 0/5V frequency is 3,8kHz and duty is 50/50. Base of the NPN is okay, too, the same signal with amplitude 0/700mV. Waveform on the piezo is attached and it seems okay for me too.
Can someone help me with this? I don't know where problem can be.

Schematic: https://snipboard.io/DMwQbx.jpg
Signal Vce with original inductor: https://snipboard.io/weDpHM.jpg
Signal Vce with 10mH inductor: https://snipboard.io/zY5fPO.jpg


Thank you.
Patrik

[Zero999]

That schematic looks wrong. The inductor should be in parallel with the piezo.

How is the piezo connected to the circuit? Is it via spring contacts? If so check they're clean.