Electrified Case (Grounding issues?)

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Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-21 @ 21:10

I recently (finally) took the plunge and bought an AT style case with an old supply in it which I'll be replacing soon.. In the mean time I was testing out the machine as is while I get my parts in order.

The computer has been off but plugged in (3 prong, GFCI outlet) for a few days now, I went in it before to swap out the sound card and noticed that anywhere I touch on the metal chassis I can distinctly feel current travelling into me, first noticed just trying to unscrew an ISA card.

This used to happen to me back when I was young and fooling with my first computer but I totally ignored it. I'd like to not cause any damage these days.

What's causing it? A leakage issue with the power supply or some kind of short? I'll take the machine apart in a little while to inspect the power switch, other then that I'm guessing I'll just have to wait for a new PSU to come in the mail. Motherboard is definitely not touching metal, using typical old style standoffs.

The evil case (not that this pic helps, can add more later when I gut it a bit).
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Re: Electrified Case (Grounding issues?)

Postby 133MHz » 2017-10-21 @ 21:41

Are your outlets correctly grounded? A slight leakage current is normal on desktop PCs when the earth ground is disconnected due to how the noise filtering is done on switching power supplies. Without grounding the case will float to roughly half of the line voltage, it might give you a little tingle or even light up a neon screwdriver but it's harmless (and disappears altogether when connected to a good earth ground). But if the leakage is significant there could be a problem in the power supply or the house wiring.
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Re: Electrified Case (Grounding issues?)

Postby kanecvr » 2017-10-21 @ 21:43

Definitely grounding issues. Could be that the outlet you plugged it in is not grounded the ground cable on the PSU is not connected to it's chassis anymore, or the power cable you're using is damaged. Most likely culprit - the power outlet.
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Re: Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-21 @ 22:15

133MHz wrote:Are your outlets correctly grounded? A slight leakage current is normal on desktop PCs when the earth ground is disconnected due to how the noise filtering is done on switching power supplies. Without grounding the case will float to roughly half of the line voltage, it might give you a little tingle or even light up a neon screwdriver but it's harmless (and disappears altogether when connected to a good earth ground). But if the leakage is significant there could be a problem in the power supply or the house wiring.


kanecvr wrote:Definitely grounding issues. Could be that the outlet you plugged it in is not grounded the ground cable on the PSU is not connected to it's chassis anymore, or the power cable you're using is damaged. Most likely culprit - the power outlet.


Thanks for the replies guys,

I'm fairly confident it's not the outlet, I run quite a few computers and devices through this and have never had an issue before. Though either way, I have a circuit tester laying around I'll dig up and check the outlets in here with if nothing solves it, I'll also swap to a new power cable and use a different outlet entirely right now.

What 133MHz said is about what i'm experiencing, it gives me a little tingle but I wouldn't call it a shock. It isn't jarring or anything, it's just notable. I wasn't sure if these old supplies had a ground cable or not, maybe that's it. This case is so small and cluttered I'll have to completely dismantle it to see.

I'm going to strip it apart now and see if there's a ground wire
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Re: Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-21 @ 22:28

photo.jpg


Crummy pic but preliminary investigation shows the PSU is grounded to the case. I can't find any stripped wires / leads touching the chassis elsewhere. I swapped the power cable and I'm going to plug it into a different outlet and see what happens.

I'm guessing if it still does it that it's not a big deal? I'm getting a new Startech 230W power supply next time I get paid, I was hoping to get by with this setup for now. I'm wondering if the same issue will continue on with a new PSU anyway.
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Re: Electrified Case (Grounding issues?)

Postby gdjacobs » 2017-10-21 @ 23:04

It's not generally appropriate for grounding purposes anymore, but you can use your cold water piping to measure impedance to the ground plug, so long as it's copper going out of the foundation or to the ground strap. A measurement of much less than one ohm is what you want, otherwise you for sure have a grounding problem.

Btw, the case bonding certainly looks good, although I can't see if it has a lock washer as well.
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Re: Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-21 @ 23:31

I haven't been able to find my multimeter for any accurate testing, waiting on a new one in the mail. I do however have a light up circuit tester that's lighting up Correct when I put one lead hot and the other ground in the outlets I'm using out here, so that's the best I can get right now.

photo.jpg


I can't find anything that looks out of the ordinary going on in here with the limited equipment I have. I cleaned that connector anyway. I just reinstalled the motherboard and made 100% sure its not contacting the chassis.

The only things to note is that this power supply is dated 1992 and the molex cables are very much dried out, but not stripped bare anywhere that I can find. Only thing left to look at is the power switch connectors, having a bit of a time getting the screw out.

Edit: I guess everything is alright. It's back together and just powered up (brand new cable that was still in its plastic bag, different outlet). Seems like it still gives me a minor buzz in my finger if i probe my fingers around inside the chassis around the rear. Seems that may build up over the course of a few days though but the hardware isn't harmed.. Maybe getting a newer PSU will solve this, I haven't gone inside this PSU to recap yet.

photoKBE763E2.jpg


Death album on top as a warning... :dead:
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Re: Electrified Case (Grounding issues?)

Postby Matth79 » 2017-10-22 @ 00:21

How is grounding done on US system, I know how it works in the UK ... 3 pin plug, and you'd check continuity from the case to the earth pin - and I've had a tingle (and the input stage of an audio filter blown to kingdom come) by suppression capacitor leakage when an earth connection had broken
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Re: Electrified Case (Grounding issues?)

Postby Jade Falcon » 2017-10-22 @ 00:30

How grounds are done depends on how old the home is. I mostly done wiring in old pre code homes witch tend to not have grounds on the receptacles plugs. the boxes are sometimes grounded to the conduit the wire is ran through then to a copper ground rod in the ground.
Post code is not the same. If I recall etch receptacles has to be grounded.


How you test it would work state side in any come post code.
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Re: Electrified Case (Grounding issues?)

Postby 133MHz » 2017-10-22 @ 00:37

Indeed there should be continuity between the metal case, the black wires coming out of the power supply and the round (earth) pin on the AC plug. You should check that out when you get the chance.
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Re: Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-22 @ 00:40

I'm not an electrician at all beyond my minor electronics projects. This house was built in the late 1980s, when we bought it I recall having to have GFCI outlets installed in all bathrooms, garage, and outdoors so the house would have been up to code as of around 2012. Those things aren't really my department though. All of the outlets in this home are 3 prong grounded outlets. When I was growing up I recall the 2 prong plugs at my grandfathers house and being dumb enough to snap off the ground pins so I could use things at their house :blah: , I would imagine this house is pretty up to snuff.

I also have tons music equipment from guitar amplifiers to keyboards and monitor (speakers) running in the garage, I would imagine a great deal of issues with that equipment with a grounding issue, or at least the hair on my neck standing up :cool:

133MHz wrote:Indeed there should be continuity between the metal case, the black wires coming out of the power supply and the round (earth) pin on the AC plug. You should check that out when you get the chance.


I'll check as soon as my new multimeter arrives. Just test between the chassis and the AC prong for continuity and I'm good? I can get at the power switch cables too. Either way I've just ordered a replacement Startech brand PSU, this one is dated early 1992, I'll play with it again in a few months when I have time to clean and recap it.
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Re: Electrified Case (Grounding issues?)

Postby gdjacobs » 2017-10-22 @ 02:59

Garage interior GFCIs are required when in proximity to ground level. You can use standard outlets if they're elevated, IIRC. The kitchen should also have GFCIs depending on proximity to the wash basin.

I suspect this is an issue with the PSU. Lots of the cheapest ones don't use proper safety rated caps for the input filter which can present this sort of shock or fire hazard as they begin to fail.
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Re: Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-22 @ 03:32

gdjacobs wrote:Garage interior GFCIs are required when in proximity to ground level. You can use standard outlets if they're elevated, IIRC. The kitchen should also have GFCIs depending on proximity to the wash basin.

I suspect this is an issue with the PSU. Lots of the cheapest ones don't use proper safety rated caps for the input filter which can present this sort of shock or fire hazard as they begin to fail.


Yep they are installed near the kitchen sink too.

I think you're right. I've exhausted about everything i can think of short of changing the psu. I'm going to hurry up and get that startech. Ill probably bump this with pics of the internals of the psu in a few weeks, i was planning on recapping it but now im not sure if its worth restoring.

I cant make out the brand without removing it. I see SPT-250 switching power supply JUN 1992 on it.
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Re: Electrified Case (Grounding issues?)

Postby CkRtech » 2017-10-22 @ 07:33

BeginnerGuy wrote:Ill probably bump this with pics of the internals of the psu in a few weeks, i was planning on recapping it but now im not sure if its worth restoring.
I cant make out the brand without removing it. I see SPT-250 switching power supply JUN 1992 on it.

I'd like to see the inside and get the full model number - just in case you are considering shrugging off that thread update you mentioned if/when you get a replacement PSU.
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Re: Electrified Case (Grounding issues?)

Postby gdjacobs » 2017-10-22 @ 14:20

BeginnerGuy wrote: Ill probably bump this with pics of the internals of the psu in a few weeks,


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Re: Electrified Case (Grounding issues?)

Postby probnot » 2017-10-22 @ 15:04

gdjacobs wrote:I suspect this is an issue with the PSU. Lots of the cheapest ones don't use proper safety rated caps for the input filter which can present this sort of shock or fire hazard as they begin to fail.

+1 on this. Modern electronics should use proper over the line caps (that aren't supposed to fail shorted), but who knows what that PSU has.
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Re: Electrified Case (Grounding issues?)

Postby RaverX » 2017-10-22 @ 16:20

I had a similar problem a while ago, I was testing a socket 7 motherboard and I was using one AT PSU "installed" on the table. So nothing was installed in a case, everything was on the table (wood table, by the way). I connected the PSU to the motherboard, then I plugged the power cord on the back of the PSU. When i tried to switch the PSU on from the power button I was "shocked", it was clearly high voltage comming from the PSU, the wire that connected the PSU to the power button of the PSU was clearly leaking high voltage. I suspect something like this happened to you. I never had such problems with ATX PSUs, only with a single AT PSU. Maybe it was faulty, maybe the wire wasn't insulated properly, but it wasn't a pleasant experience.
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Re: Electrified Case (Grounding issues?)

Postby Maeslin » 2017-10-22 @ 20:17

RaverX wrote:I had a similar problem a while ago, I was testing a socket 7 motherboard and I was using one AT PSU "installed" on the table. So nothing was installed in a case, everything was on the table (wood table, by the way). I connected the PSU to the motherboard, then I plugged the power cord on the back of the PSU. When i tried to switch the PSU on from the power button I was "shocked", it was clearly high voltage comming from the PSU, the wire that connected the PSU to the power button of the PSU was clearly leaking high voltage. I suspect something like this happened to you. I never had such problems with ATX PSUs, only with a single AT PSU. Maybe it was faulty, maybe the wire wasn't insulated properly, but it wasn't a pleasant experience.


You have to be careful with AT PSUs, the power switch on them is often wired directly inline with the AC power cord. ATX supplies have a 'smart' switching circuit that runs off the 5V standby source.
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Re: Electrified Case (Grounding issues?)

Postby BeginnerGuy » 2017-10-22 @ 23:26

CkRtech wrote:
BeginnerGuy wrote:Ill probably bump this with pics of the internals of the psu in a few weeks, i was planning on recapping it but now im not sure if its worth restoring.
I cant make out the brand without removing it. I see SPT-250 switching power supply JUN 1992 on it.

I'd like to see the inside and get the full model number - just in case you are considering shrugging off that thread update you mentioned if/when you get a replacement PSU.


I'll crack it open later this week when I have some time, didn't think there would really be interest. Right now it's back together for some light use. I went ahead and ordered the replacement PSU from amazon so I'll have this one out in a couple of days.

gdjacobs wrote:
BeginnerGuy wrote: Ill probably bump this with pics of the internals of the psu in a few weeks,


Image


hahah
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Re: Electrified Case (Grounding issues?)

Postby gdjacobs » 2017-10-23 @ 00:24

Dueling Kirks?

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