I got zapped earlier today...

[skatingbasser]

I was disassembling a practice amp several hours ago.  Once I got it all apart, I was trying to make sure it was still working before moving on.  I turned it on a saw blue sparks, so I immediately turned it off.  I went to unplug the little bugger and got zapped, on the harsch side.

Came back to it and it will not power on.  My first instinct was the fuse, I looked, but it wasn't cloudy.  I couldn't see anything actually, it was completely clear.

The only thing I can think of that is different from when I started is the peice of material under the main ground may have been jostled around, leaving the ground to touch the metal chassis.  Could that mean anything?

I am stumped, can anyone tell me what happened, or what do to?

Thank you in advance for any help, I am quite the noob at this.

[WorkBench]

The chassis is the ground, so the ground coming into contact with it should be whats happening at all times.  Can you see a small line in the fuse, like a rail running the entire length?  The little metal strip that actually carries the power thru the fuse should still be visible at least!  If not pop in a new fuse and let us know.  Is it Solid state or is it a tube amp?
Chris

[barret77]

I got zapped by a  tube amp once, oh boy, spent one day with hands trembling...

[Hal]

idealy, use a meter to test the fuse.  If you dont have one, use an LED, resistor and battery - put the fuse in series and see if the LED lights up!

[skatingbasser]

Yeah, I couldn't see anything, no rail or anything.  It's a solid-state amp.  I don't know where any LED's are, so it looks like I can't do much tonight.  I'll pick up my soldering gun tomorrow/look for my bag o' fuses and try that; I'll keep you updated.

Thanks everyone!

[RLBJR65]

You should be feeling extreeeeemly lucky right now, even small amps are run on voltages that could easily kill you! When you are working on anything that plugs into mains you need to be very very carefull. Also you need to be aware that even with it unplugged there could still be capacitors in there charged with enough juice to kill you.

[Transmogrifox]

And to think in the old days the electrician would lick his fingers and put one on each phase to determine whether it was 220 or 440 by how much it tingled his hand.

[zachary vex]

i got zapped with 400VDC one day in high school and was unable to play my cello in orchestra a couple of hours later.  it can really mess up your muscles and your mood.  glad you weren't hurt.

check your fuse with an ohmmeter.

[mlabbee]

Indeed.  I once spent an evening trying to figure out why my lights woldn't go on. I checked every fuse about 30 timews (pre breaker days - I'm dating myself).  A very irritated roommate just went ahead and replaced the fuses. Oila!  Lights go on.  fuses can look fine and be blown . . .

[MartyMart]

BE CAREFUL !!!
Mains voltage is WAY WAY more than a 9v pedal battery, which you can put your tongue across to check whats left !!!

Cheers,
Marty.

[Johnny G]

so far i havnt been zapped myself but i have a friend who got blown across a room when he was younger after putting keys into a mains socket lol. he learnt that lesson and got to sit for 2 hours twitching slightlly

oh and zach....u play cello? :shock:

[Satch12879]

For chefs it's getting seriously burned with hot oil...

For architects it's cutting your hand with an X-Acto knife bad enough to require stitches...

For amp repairmen it's getting shocked bad enough to feel it...

What am I talking about?

Rites of passage.

You're now officially a tech! :mrgreen:

[noesis]

even small amps are run on voltages that could easily kill you!

i think this is incorrect.  it is the current that kills you, not the voltage.  something around 100 milliamps would be sufficient.  that is why it is possible to survive being struck by lightning.  over a million volts, but no amperes.

BE CAREFUL !!!
Mains voltage is WAY WAY more than a 9v pedal battery, which you can put your tongue across to check whats left !!!

BE CAREFUL putting a 9 volt battery onto your tongue, which can be fatal.

[skatingbasser]

So, does anyone actually have any tips for how to go about "being careful?"  I mean, I can't really think of anything besides the obvious unplugging the amp before tinkering around in there.

And I'd just like to thank you all for making this such a nice, friendly community.

[maximee]

unplugging the amp is by far not enough!
you should be pretty damn careful with those BIG capacitors....they are most likely charged after unplugging and can also give you lethal shocks...

i suggest you stop working on line-voltage-stuff until you are familiar with all the possible (and not to forget: LETHAL) dangers involved for your own safety...
:!:

[object88]

If I understand correctly, one thing you can do is drain caps with a lightbulb.  Wire up one of those ceramic bases with a couple of leads, screw in a bulb, and put the wires across the cap terminals.

Is it safe?

[Transmogrifox]

Is it safe?   I guess it depends how you do it.  If you're being cautious and you get the lightbulb to absorb all the energy stored in the capacitor, yes it's safe.  If you slip and your body takes the energy, then no, it's not save.  I know one guy who unplugs the amp while the power switch is "on".  He thinks it bleeds the voltage off the caps--not necessarily so. Usually there is a transformer and rectifier and the only way around that direction is through the rectifier, which is designed to keep current from flowing back out of the transformer in the opposite direction.  The caps are still charged until they bleed out slowly on their own through the resistive networks to ground, which in a guitar amp can be relatively large.

I personally haven't had trouble with large voltages lingering on the caps in my tube amp for a long time after unplugging, however a different amp will bleed or not bleed a different way, so we can't simply assume the caps have bled out.  I still don't approach my amp without treating it like anything on the circuitboard is hot, ready to jump out and zap me until I have checked everything with a multimeter.

If you touch anything in your amp (after you have made yourself pretty confident it's not hot), then whatever you touch, first tap it with the back of your hand for 2 reasons:

1.  An electric shock causes the muscles to contract.  If your hand is in a position that it can't grab onto anything when it spazzes, you can still pull away.  Otherwise, your hand my grab something hot and then you're really in for it because you won't be able to let go until it's completely discharged everything into you.

2.  The back of your hand is more resistive than fingertips/inside hand, as your fingers generally have more perspiration, salt and mineral oils on the front "grabbing" side of your hand.  Therefore, the back of your hand will likely work as a somewhat better insulator to minimize current flow through the body.

I think we're usually pretty safe after the power has been unplugged on little solid state practice amps, though it doesn't hurt to take a meter to the caps or short them with a light bulb.  I don't want to say anything that will cause somebody to be careless because you could be seriously killed by a 12V battery if you were covered in salt and wet (could happen after a marathon).  You get done running a marathon, want to go home, but your car doesn't start so you start playing with the battery after dumping water over your head to cool off....maybe not.  NOw I'm just rambling for the fun of it.

[Paul Marossy]

When I was in my Octal Fatness a few weeks ago, I forgot to unplug the power cord. While I was soldering some stuff, my hand accidentally touched the IEC socket and I got zapped with some 120VAC. I pulled my hand away immediately when I felt that "getting shocked feeling" that I am familiar with. So later on the next day, I proceeded to do the same thing again, not once, but twice!  :oops:

[Hailstorm350]

Ok here's the diddly-o.  (did I just say that? :shock: )

To die from electricity all you need is any amount of voltage above 0.1 V ( I think )  and a minimum of 100mA  ACROSS THE HEART.  I read somewhere that it is actually as low as 20mA  but everywhere else seems to say .1A or 100mA.  The reason people don't die from touching a mains outlet is simple:  The current does not flow through their heart.  If you touch one prong of an AC outlet with one finger on one hand and the other active prong with another finger on the other hand, It is almost impossible to survive unless you by chance and happiness including the grace of god that you touched the earth ground connector, in which case it is still very unlikely that you would survive.

I would suggest what I read in rich flieglier's book ( I think I spelled his name right). The poke and push method.   :lol: use a chopstick or similar shish-kabob wooden tool to poke things around if you must.  And what I did with my real mc-tube whenever I needed to go into it immediately after plugging it in was use a screwdriver ( large resistance)  and rub it up against one of the power capacitor contacts and the chassis.  Because the other end of the capacitor was grounded eventually through the circuit to the chassis.  Whenever I did this, sparks would fly but because the combined resistance of the screwdriver and the chassis was so huge, the power disappeared almost immediately.   This is what I did.  Note:  I WAS holding the end of the screwdriver with my hand but I was not touching the chassis with my other hand.  I do not know what the internal resistances of the body are but i can imagine that they are quite huge and probably larger than that of the screwdriver/chassis  which would explain that if I had been touching the chassis and the screwdriver at the same time,  the electricity did not flow significantly if at all through me.

Phoo, that's enough for one night.

Oh and good luck with the repair skating bassist

Ken

[analogtom]

Ok here's the diddly-o.  (did I just say that? :shock: )
And what I did with my real mc-tube whenever I needed to go into it immediately after plugging it in was use a screwdriver ( large resistance)  and rub it up against one of the power capacitor contacts and the chassis.  Because the other end of the capacitor was grounded eventually through the circuit to the chassis.  Whenever I did this, sparks would fly but because the combined resistance of the screwdriver and the chassis was so huge, the power disappeared almost immediately.

I'm surprised in 2 pages of replies, this is the first mention of that. An amp tech showed me that one. I never saw any sparks. He just took that screwdriver and put the tip on the end of the cap and touched the side of the screwdriver to the chassis. And of course, the screwdriver had a plastic handle. He did that to all the big electrolytics and kept his other arm behind him while he did it. They were apparently completely discharged.

Be that as it may, I'm still too chicken to work on my amps, which is too bad because I have a tweed Champ and BF Princeton Reverb that could use a going over. But I think I'll stick with the pedals for now.