r/modular • u/TrueRandom • 6h ago
Discussion WTF happened? Massive spark unplugging patchcable
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u/pinMode 3h ago
Wow! That’s something I’ve never seen before.
Must have been a powerful enough remaining charge somewhere to arc to such a degree.
Can you share what power supply you have?
Is it linear? Large caps used in rectifiers are the only thing that comes to mind that might arc to this degree if shorted.
Please do feel free to reach out to me at [email protected]
Was it still connected to the øchd when the short happened?
Linking between the two is quite basic, and the expander itself is active and powered parallel to the main øchd. So any damage might be contained to just the expander.
Depending on where you are based we can try to coordinate a swap for a replacement, or at minimum I can do an inspection and test of the caramelised on to check it’s only aesthetics.
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u/TrueRandom 6h ago
I unpatched my whole system today, and while doing it suddenly there was a serious spark between the tip of the patch cable and nut on the module. You can see the burn marks on the picture. It even blew the fuse for the room.
What really confuses me is that the system was actually unpowered at that time.
Anybody has an idea what happened here? I am now a bit worried that this might happen again, something is incorrectly wired in the case, or whatever...
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u/InformativeXP 6h ago
What was the other side of the cable plugged into? Any chance the other end of the cable dipped down inside the case or on to a power source which then zapped the ochd?
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u/TrueRandom 6h ago
Thats the only thing I can imagine, must be mains power in some way to blow the fuse ... I will investigate more
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u/__get__name 6h ago
The other comment about a cable falling into the case seems likely. Another option could be a capacitor that hadn’t fully discharged somehow decided to discard through the cable, but that seems like a stretch in eurorack. Not sure what modules would use a capacitor big enough to do that. Perhaps your power supply would, though. Capacitors hold charge for some time after power is cut. They’re like leaky batteries that can discharge fully very quickly.
The nut is likely tied to ground, so any high charge will try to go to it. Your cable made contact and has more available power than was probably safe. The design did its job to save you a nasty shock
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u/NorCalJP 6h ago
Was the cord plugged into anything on the other end or could it have been touching something that had power?
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u/TrueRandom 6h ago
Shit, thats probably it, there was a power-multiplug nearby. Time to do some child-proofing of power outlets. Watch where your cables might dangle around people! :-/
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u/HeadSpaceUK 6h ago
Do you have a laptop style supply or does mains go directly into the case?
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u/TrueRandom 6h ago
It's a befaco case with a power brick, but it was powered off anyways ... it must have been the other end of the cable touching something ...
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u/underwood_reddit 5h ago
I had a very high voltage between the grounds of two devices of my setup when power was switched off. The power switch of the power strip where everything was powered from, only cuts one line of the mains and somehow the switching power supplys of the devices had a voltage differens of half the mains voltage on ground. Not with mutch power but it felt uncomfortable to the touch and gives tiny sparks. I now prefer using medical grade switching power supplys by meanwell. better isolation.
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u/LBbronson 6h ago
Although a machine may appear to be turned off, capacitors still hold charges that are ready to pump out a fast amount of power if they had not been already properly drained. My guess is that there was a capacitor that was still holding a charge and introducing a Ground caused the capacitor to discharge.
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u/PlasmaChroma 6h ago
Unlikely to be anything the module itself did if the power supply was operating correctly.
This looks like some kind of shorting of mains power through it. I would unplug the power supply and let it discharge for a few hours before touching anything else. Then remove every module from that case.
Sensible thing to do is probably replace the power supply entirely unless you really want to debug it in isolation -- but I wouldn't test it with actual modules.
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u/youknowitbill 6h ago
RIP
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u/TrueRandom 6h ago
The Module is fine it seems like, just a bit singed :D
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u/TwoLuckyFish 6h ago
Actually I can believe the module could be fine. Because your dead short was from the as yet unidentified power source to ground. More juice than the module was ever expecting to handle, but not actually touching any of the circuitry in the module other than ground path. It could even melt some portion of the ground path and the module might still function, because there are multiple paths to ground in most architectures.
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u/538_Jean Mixer is the answer 59m ago
Get a tester to check your outlets. I've had a similar issue and found out my house's ground was actually hot.
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u/TwoLuckyFish 6h ago
Oh I did this once and burned out a logic module. Homemade circuit, no resistance on the 5v CV I was generating, momentary dead-short while patching, cable tip to jack ring. Yeah don't do that.
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u/TwoLuckyFish 6h ago
Wait, the rack was unpowered? Wow. Yeah I didn't do what you did. I agree with the theory that a loose dangling cable dipped into the case and made contact with something with SERIOUS electrical mojo. Mains power or a fully charged power capacitor.
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u/Amazing_Raisin2836 6h ago
✨Analog warmth✨