Loud pop on board while recapping

[Pentium4]

So I guess I was kinda stupid...I pulled apart an HP monitor because I suspected bad caps (Oh boy, all CapXon) while I was replacing one of the caps, when I bent the negative lead down to hold it in place and when it touched a grounded pad I heard a loud POP! and there was a small burn mark on the trace (it doesn't go anywhere) I checked the 3 caps I had pulled and they all still had 8V of charge in them.

I assume after this pop happened, that discharged the remaining power being held? The big input cap only has 1.1V in it after this happened. I will upload a picture tomorrow

[luke10050]

Re: Loud pop on board while recapping

im pretty new to this but did you see any bright lights or anything? the pop could, COULD have been the air ionising between the ground and the lead meaning that the board arced out... did you try the board again? i know big caps can arc out pretty bad (nice flashes and a bit of a pop) no idea if it would cause damage to other parts of the board though.

so yes it probably discharged the remaining power in the circuit

Edit: you probably should have discharged all the larger caps with an INSULATED screwdriver rated for 400v+ before working on it, chance it could have been you going pop (discharge them by bridging the terminals, they can store lethal charge for a few days if i remember) Please correct me if i am wrong!!!

[Pentium4]

Re: Loud pop on board while recapping

No bright lights or anything. I guess I should check the fuse, it could have popped. I have not tried the board again, it wasn't a main priority so I just walked away for the time being

[cheapie]

Re: Loud pop on board while recapping

I think you just discharged the primary cap. It should be okay.

[Pentium4]

Re: Loud pop on board while recapping

I will replace the caps I have removed and then plug it in to see if it's still working before I spend any more time on it

[retiredcaps]

Re: Loud pop on board while recapping

On the an LG 22 inch monitor, the big filter capacitor helds its 165V DC overnight despite being unplugged from the wall socket.

Good thing I always check the big filter capacitor with a multimeter (with aligator clips if possible) first before doing anything. I had to discharge using a 100K ohm resistor.

[Uranium-235]

Re: Loud pop on board while recapping

as long as you don't discharge it connected to any other parts, you should be ok with a short discharge.

My dad was such a bastard back in the day. My grandfather worked on A/C units then, my dad brought a fully charged oil cap to school and discharged it against his desk. Made a big hole in the metal

[ben7]

Re: Loud pop on board while recapping

^agreed. LOL what a crazy dad!

I have had my own share of accidental/surprise capacitor discharges.

[momaka]

Re: Loud pop on board while recapping

I've seen some power supplies also hold charge on the secondary side for a fairly long time as well. Like the power adapter for my laptop - it will hold 20V for about 10 seconds. If you accidentally short the outputs when it's still charged, it almost always throws a huge spark and makes a loud pop. Not as bad as shorting charged primary capacitors, though.

I have had my own share of accidental/surprise capacitor discharges.

Same here.

One of the worst was when I accidentally discharged a 450V 180 uF cap through my thumb. It was the main capacitor in a HP TV and it would remain charged to 400V for a few minutes. Felt kind of like a nasty bee sting but the pain went away much quicker.

I doubt the charge in those things is lethal, though. However, if you discharge it in such a way so that the discharge path goes through one of your hands and exits through the other, it will probably hurt A LOT more, and you'll be sure to remember it very VERY well.

[c_hegge]

Re: Loud pop on board while recapping

If you had a weak heart, it might kill you. I've been hit by PFC caps in power supplies a few times when I opened the PSU just a few minutes after being plugged in. I guess I'm just too used to having bleed resistors discharge them on non-PFC designs.

[goontron]

Re: Loud pop on board while recapping

so it took 10 posts to say you need to respect electricity or it will try to kill you and that you shorted a charged maines cap!