Mystery magnetic sounder problem

I had a minor mishap at work today and I'm hoping you guys might be able to shed some light on it. I was doing something in work involving attaching wires to sounders - a simple job. Sounders in parallel at one end, hirose crimp connector at the other. For some reason, even though they continuity tested OK, they failed their functional test in which a signal is pumped in and the dB levels measured - they were far too quiet and some sounded crackly. We can't find any problems with the test gear itself, and it doesn't look like there's an issue with the brand new ones in the tube.

Can these things be damaged by cleaning with IPA after soldering? I'm wondering (and it is a bit of a long-shot but so far we can't figure out why they're buggered) if flux residue dissolved in the IPA has gone up inside the thing and hardened again, messing with the little diaphragm somehow. Any ideas on what to try? It'd be nice to rescue them and not have to re-do the entire lot. :)

All of the 3 and 5V sounders I’v used in production have always had a seal tab covering the sound hole so that it doesn’t become a solvent hole. 2 things come to mind, 1. The sounder internals may be soluble in IPA (the glue used in assembly and thus damaged ). And 2. The IPA has a great deal of water in it and the water hasn’t dried yet. Don’t remove the ‘stickers’ until all fab is completed on the PCB that uses the sounder.


Wouldn't driving multiple 'sounders' in parallel lower the circuit's effective impedance cause an over all loss of amplitude if the driving test source has a fixed or current limited output impedance? Is this an electrical test procedure that has worked effectively in the past with identical 'sounders' and test equipment setup?


No idea, Lefty! It's not my design :) But the test itself has been unchanged for years... I can only assume those who designed the setup know what they're doing.

The sounders don't actually come with seal tabs on them (which seems odd, as all the ones I've actually bought came with them and I don't normally pull them off until I'm done with them). If the IPA has done something horrible to the innards then I suppose there's little I can do other than apologise and make some more...

I wonder, is it worth opening one up completely to investigate any possible internal damage? We've got thousands on the shelf so I could compare a new one to one that I've molested to see if there's any difference.