EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: erikbrenn on June 27, 2018, 10:34:23 pm
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Hi,
My son's headphones stopped working today. I figured he had stretched the cables or something but that's not the case. I opened them up and verified that there were no loose cables.
I startet a testsound video on Youtube and hooked up my Tektronix and probed the solderpoints, and it seems the incoming signal is perfectly ok (attached image). My Tek reported the same freq as the youtube video.
What could be the reason that none of the transducers generate sound? Hard to believe that they can suddenly become defect.
https://imgur.com/a/kjiiHFs (https://imgur.com/a/kjiiHFs)
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Quiet amazed that you managed to hook up the scope but did not check resistance of the speakers and wires in the cable.
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A speaker, in essence, is still a piece of wire electrically, so odds are good there's a break. It could also be that the cone the electromagnet coil is attached to is damaged in a way that it can no longer make sound, but odds are better that a connection is broken - for example one of the flexible ones that run directly to the coil.
It could be that it shook loose with use or if overvoltage burned out a turn in the coil.... doesn't really look like there are additional electronics in your headphones, but something in there could be damaged if it exists. Also worth changing to a different source - maybe the output has failed in that it works normally but can source very little current, so it can't effectively drive a load as significant as headphones.
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Hi,
I can’t see very well on your photo how you are measuring with your scope probe. Is ground connected by some separated wire or are you probing both ground and tip directly on the comtacts of the headphone?
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Hi,
I can’t see very well on your photo how you are measuring with your scope probe. Is ground connected by some separated wire or are you probing both ground and tip directly on the comtacts of the headphone?
It rather seems he probes with ground clip unconnected. If signal source is grounded, then there will be signal measured even if ground wire in headphones if broken. Still it's completely ridiculous to check passive headphones with oscilloscope.
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Thanks for advice and comments, perhaps I don't deserve a scope :) I just scoped to to see if there was a signal and it was, so I figured something with the speakers, hence my posting. After posting I realized that all three solder points from incoming wires had signal, thus had to be a short in the cable. I desoldered wires and cut my way down to a short/stretching damage 10 cm below the headphones. After fiddeling with these thin enamel coated wires for a while the headphones are working fine again. Kinda feels good to have repaired them...
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After posting I realized that all three solder points from incoming wires had signal, thus had to be a short in the cable.
More likely that ground wire was broken and you have seen signal which came through rather low resistance of the speakers.
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Ah, of course, very likely indeed... I ohmed the speakers and they were around 50 ohms.
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Happy you fixed it.
Next time it’s better to simply use your DMM and ohm out the individual wires. As wraper explained it’s likely your ground wire was broken.
If both your scope and generator (PC I guess as you explained you used a youtube video to generate the test sound) are grounded, then your broken ground wire was bypassed and disguised by the mains earth wires of the pc and scope.