another smoke alarm thread.

[Brian Gaff]

Which reminds me, A smoke alarm here has a strange fault. This makes the sounder very quiet, and it can only just be heard. Tap the box and it bursts into life. I think it might have got a foreign body in the sounder, which gets trapped and stops it resonating. Two thought was, I could just unstuck it and fit a new one, the safest option I guess, but not wanting to throw away something that might be fixable. Assuming no foreign bodies can be shaken out of the sounder, I wonder if just getting a sounder and soldering it in might be ok, or might the actual sounder cost more than the alarm? It would be a friend soldering it in, but from the feel of it it might be doable with a chock block!. Its finding a sounder that fits. Brian

[newshound]

I'd have thought it was far more likely a foreign body giving a false trip current signal in the detector cell. If vigourous shaking, vacuuming, or perhaps puffs from an air duster don't sort it I would sling it in the bin.

[Dave Liquorice]

More likely a dry joint somewhere. get your friend with the soldering iron to have a close look and maybe reflow the sounder connections. If that doesn't find anything or cure it, bin it and get a new one

[alan_m]

Or a dry solder joint and tapping it causes the contact to be made more firmly.

Either way, how could you be certain that you have fixed the fault? Messing around with it would be the same as tapping it to bring it into life. The original fault may still be present and kick in hours after you put the alarm back on the wall and in a real fire you may not hear it.

[Brian Gaff]

No its definitely the sounder. The burnt toast test trips it OK but the sounder can hardly be heard, a tap and the sounder is fine again. If it was in the sensor then it would be the opposite fault, ie going off all the time.

Pay attention at the back boy! Brian

[charles]

My thought would be a dry joint.

[charles]

but having thought further, the battery connection may be the problem. Low current, sensor, is fine but once the sounder tries to start the current loading shows up a poor connection. This could well respond to a touch of percussive maintenance.