Shock from My amp!

[Steve A.]

If chassis is properly grounded there should be no shock hazard. Check for voltage between amp chassis and 3 prongs of AC socket.
There should be 120vac between chassis and hot (skinny flat prong in AC socket.)
There should be 0vac between chassis and neutral (wider flat prong) and ground (round pin in AC socket.)

Steve A.

[R.G.]

Which does beg the question "Why is the OP getting a shock?"
How is a voltage potential being developed between the amp & the guitar.
Even ungrounded, there should not be any voltage on the chassis.

Aye, thae's the rrrriddle.
And Enzo is on it as well. We don't have a lot of info.

I homed in on the "after a few minutes" part. I'm wondering if there's an AC line MOV in there that has floated down to near the AC line peak and is starting to leak when it gets hot. Likewise, The OP could well be on it with suspecting the X and Y rated safety caps. Or any of several other places where AC line is insulated from secondary ground an is leaking.

We'd need more info to make a better guess. How much shock, what conditions, multiple buildings, how long it takes for it to happen; hey, houw about a voltmeter sampling the "shock" for how big it is!

@OP: Forgive me if I have underestimated your skills and experience, but your comments lead me to believe you don't have a lot of experience with AC mains circuits, or with switching power supplies. Maybe you do, and I just missed it.

If so forgive me, but we hate to lose budding amp-fixers to dying by electrocution. I used to design switching power supplies for a living, and I hate to go poking around inside them. It may well be that some simple component is soft failing and a simple desolder/resolder would fix it. But unless you really have the skill and experience, a trip to a tech to fix it is much cheaper than a funeral.

[Mick Bailey]

There are quite a few SMPS supplies that will float the output at about 60v-80v with reference to mains earth - enough for some people to get a shock or tingle, and common with some ungrounded laptop supplies. Whenever I've encountered this with equipment provided with a chassis earth there's always been a fault present and sometimes this has been on the mains side external to the amp (bad extension lead, faulty cable, plug-top, step-up auto-transformer or even a house with an earth fault). My first check is to measure the voltage between the chassis and an independent (verified) mains earth connection such as a cold water pipe.

[jajabinker]

Cannot reply to my own thread

Dear admins i cant reply to my thread, shock from my amp!


When i try to post i get a message saying that my messages have to be approved by an admin. But its been a week and I cant do anything.

Sorry for making a new thread but i dont know who else to ask.


Thanks and regards,

Jonathan

[J M Fahey]

the earthing fails. If i connect an external earthing wire to the chasis, the shock stops.

Then *clearly* you have a grounding problem.

***might*** be inside te amp, anything can fail, but I very much doubt it, doubly so coming from Lawyer-aware Fender Corporation.

Caps are probably related to it but not faulty ... very often, for RF protection issues, there is one cap from Live to chassis, another from Neutral to chassis.

IF chassis is properly grounded, both do their duty (shunting RF, HF, pulses, spikes) to ground and nobody´s the wiser.

But if chassis is poorly or not grounded, both caps in series form a voltage divider, and if you have 120V mains, chassis will end at about 60V AC from ground

Something like that was mentioned above and this is the reason.

Are the caps broken or wrong?
NO, they are doing their job ... it is Owner´s fault not providing proper Ground, so go and solve that first.

Do not mess with he SMPS nor touch its caps.

[J M Fahey]

Hi Guys, looks like the OP can't get in, maybe the Software "built a Wall" and will later proceed to charge him

Im a new member and i cant reply to any of the comments on the thread i have created about "shock from my amp". For every reply a message says i have to await moderation. But its been more than a week. I don't know whom to contact about it, can you help?

Can somebody with due powers help him?
Thanks.

[nosaj]

Hi Guys, looks like the OP can't get in, maybe the Software "built a Wall" and will later proceed to charge him

Can somebody with due powers help him?
Thanks.

maybe built in spam bot protection?
nosaj

[Enzo]

I think someone has to turn off the newbie switch. If tboy isn't watching, maybe Steve?

[g1]

Reporting myself to flag this post.

Admin: Please see post #13