Melted TOSLINK Cable Plugs – Ever Heard of This?

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I don't have a lot of experience with optical cables, but my father called with a strange issue last night. He was rearranging his AV cabinet and noticed when he unplugged his AT&T U-Verse cable box from his passive TOSLINK switch (cable and PS3 in, out to Bose all-in-one) that the black plastic plugs of the optical cable had melted, pooled, and hardened at both ends (switch and cable box) – he actually had to chip material out of the bottom of the jacks with a jeweler's screwdriver. The cable was occasionally intermittent, but mostly worked fine until he removed it.

I can't imagine the optical signal generates any appreciable amount of heat (and the fiber seemed fine). I'm sure the AV cabinet got a little warm, but I doubt it was anything out of the ordinary – and a second TOSLINK cable of identical manufacture was connected to the same switch and it did not experience any issues. This seems to rule out ambient heat and "bad batch" issues. I'm sure the cable box gets a little warm, but that would only explain the termination on one end of the cable – I can't think of any mechanism that could transfer the heat from one plastic plug to another several feet away.

Any thoughts on what could've caused this? We are both at a loss.
 

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There shouldn't be anything close to enough heat to melt plastic connector ends. A simple test would be to power the cable box and allow it time to warm. Then, hold the bottom of a thermometer on to an empty jack to see if the temperature rises alarmingly. If yes, I can't help but believe there is some sort of dangerous fault inside the cable box. If not, the only other thing I can think is that perhaps the cable plugs were subjected to some sort of chemical solvent.

P.S. Don't use a finger touch test because if the jack is hot enough to melt plastic, it's hot enough to give a very severe burn.
 
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Chemical reaction does seem the most likely.

Any heat from the electronics of the TOSLINK receiver/sender would be down to a fault in the Rx/Tx module and as such it would literally be toast and non functional. You don't need much current at say 5 volts into a transistor or IC to generate significant heat but its all so unlikely.

Chemical reaction or someone using some substance on the plugs gets my vote.
 
Maybe it is a plastic manufacturing defect or error?
I've seen household electrical wiring internal insulation production fault - after few month or so of usage - internal insulation of electrical wire looks like honey and and it flows down from the wall sockets..cable still working fine.
 
Had a similar issue with an HDMI cable , back when this type of connection was relatively new ( and expensive ) i purchased a 0.75 m cable for GBP 70 to connect my PLAYSTATION 3 - LG 32 LCD.
Fast forward 7 years and i started getting an occasional black screen fault which got progressively worse and more frequent.
Upon investigation i discovered that the plug housing had completely melted away at the PS 3 end as had the outer cable shroud along about 60% of its length.
The plug at the tv end was intact but distorted and out of shape and had obviously been subjected to high temperatures .
Although a PS 3 does produce some heat it had been on a rack and not enclosed as had the tv and the fan in the PlayStation had never gone over the 2nd of the 3 speeds it had , and then very rarely and briefly.
I could find no reason or explanation for the cable getting hot enough to self destruct especially at the ' cold ' end .
The cable ' PROWIRE ' had a lifetime warranty and i had kept the receipt but the shop refused to replace as they said it had obviously been in a fire and , quote , ' there's no way that would happen in normal use ' .
In the end i gave up purchased an HDMI ( elsewhere ) for GBP 10 and used it in the same set up for about another year until i upgraded the console and tv , the cable was as good as the day i had installed it , so yeah heat + chemical reaction = LOTS of heat ? guess it'll remain a mystery .
 
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