JL Sargent Posted July 22, 2009 Share Posted July 22, 2009 I have a 20w megaphone. I bought it inop. for 5 bucks at a yard sale. It works off D size batteries and those are good. When I pulled the trigger to turn it on I could hear a click but no voice was amplified. I took it apart and measured resistance across the mic's coil which is about 500 ohms. Well I put it back together and it worked! I have figured out that measuring the resistance is applying a DC voltage to the coil and kinda waking it up. So I took it a step further and applyed a 9v battery to the leads momentarily. I could hear the coil react rather strongly. Maybe a 1.5v AA cell would have been better. Anyway, its been working fine now for quite a while. What did I do? The mic looks like a little speaker with a clear rather flat diaphram instead of a cone. Quote Link to comment Share on other sites More sharing options...
Professor Thump Posted July 22, 2009 Share Posted July 22, 2009 The coil may have been stuck in the gap or you fix the contact point to the amp. IMHO... Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted July 22, 2009 Author Share Posted July 22, 2009 After I would check resistance across the coil the unit would work right for 5 minutes or so and then I would have to recheck to wake it back up again. Now after doing the 9v deal it continues to work when I try it and several hours have passed. I was thinking maybe something magnetic? Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted July 22, 2009 Author Share Posted July 22, 2009 Just tried it again and no go. So the 9v battery hit lasted 6 1/2 hours. Maybe the mic's magnet is weak and the battery remagnetizes it for a while? Or the mic acts like a capacitor? I dunno. Quote Link to comment Share on other sites More sharing options...
djk Posted July 23, 2009 Share Posted July 23, 2009 Just replace the mic. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted July 23, 2009 Author Share Posted July 23, 2009 Just replace the mic. I know its a crazy concept, but actually trying to learn something here.[<)] Quote Link to comment Share on other sites More sharing options...
boom3 Posted July 25, 2009 Share Posted July 25, 2009 have you cleaned the contacts in the trigger? If you have continuity across the coil it is more likely a contact problem in the trigger or battery holder. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted July 25, 2009 Author Share Posted July 25, 2009 Yeah, I have it down to a science now. Simply touch a 9v battery to the Mics contacts and the thing works great until the next morning. That gives my 5yr old plenty of time to act like extreme home makeover's Ty Pennington. I suspect it has to do with the mic's magnetic properties but I don't know. Quote Link to comment Share on other sites More sharing options...
Professor Thump Posted July 25, 2009 Share Posted July 25, 2009 The magnetic value doesn't change. It has something to do with the phantom power (VDC bias) to the mic I would guess. I am assuming this is an electret mic now. You probably have a shorted diode draining the battery or something like that. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted July 25, 2009 Author Share Posted July 25, 2009 You may have something there Prof. Thump. I notice there is pot accessible from the battery compartment just under the mic thats labeled "adj". Maybe I could give it a 1/4 turn clockwise increasing that fwd bias enough to keep the mic working. This unit will do siren, fog, and voice. The siren and fog functions work great consistently. I have not changed the batteries since buying. Quote Link to comment Share on other sites More sharing options...
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