Question Weird Issue Where Amp Cuts Out Headphones Still Work But Heat Up Until Broken!

Sep 11, 2019
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I have a very strange issue I’ve never seen/heard of before. I have an old Aurex SC-M15 Power Amp with it’s matching Pre (no tape or tuner connected), it started cutting out. I tested the headphone out and that still worked, but it started heating up the ear bud on the left channel, really hot, to the point it’s damaged and now outputs a lower volume distorted sound.

I know a lot about music and a good amount about the related devices and electronics, and I’ve never heard of this happening before. I attempted to diagnose the problem, but with no luck.

First I thought it was one of the inputs, either wires or connectors, but nope. I tested the headphone output very briefly to check it worked, and it did. So I then thought it was the speaker wires, but again, nope.

So then I spent a bit longer with the headphones, and that’s when I noticed the heat. Not only that, after heating the earbud up to the point it broke, I suddenly realised I’d used much better headphones the first time I checked, so I re-checked that pair, and of course, the left channel was also broken in the same manner.

What on earth is going on? The output signal not reaching the speakers I would guess is just a loose connection inside, but then the headphones heating up till they break? Again, just guessing, but wouldn't that mean they are being over powered somehow? Perhaps what’s broken inside is driving more power to the headphones, whilst not reaching the speakers?

Another factor that may have something to do with it is that the stereo is runs on 100v and I live in Thailand where the power is 220v, so I have a step-down transformer in place. Wondering if that might have something to do with it, although I’m not sure why it then hasn’t blown anything else.

This is power amp in question (the pre amp isn’t pictured there, but that seems to be fine, it’s this power amp that’s the issue)
https://www.radiomuseum.org/r/toshiba_stereo_power_amplfier_sc_m15.html

Any ideas? Ever head of an amp making headphones so hot they break? Language barrier makes a little hard to just take it somewhere and expect it get fixed at reasonable price with a decent explanation as to what was wrong. I would imagine I"m going to have to do that anyways, but going in armed with a good idea of what needs doing, how and why, it's a good way to help the transaction go somewhat smoother.

Thanks in advance for any info or suggestions. Cheers.
 

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