Atari Big Blue replacement

learpilot2

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I am new to the hobby, and am about to replace my Atari Big Blue Cap. I was wondering if I need to discharge it before messing with it. Was not sure if it holds enought current to shock me. Also wondering how to discharge it. Just connect the negative pole to the monitor chasis?
 
I have never had to discharge it and I have replaced Big Blue on 5 different machines. I guess there is a slim possibility it could hold a charge but I doubt it. You can properly discharge it using a large wattage resister and putting it accross the screw terminals. Or you can just us a screw driver being careful to only hold on the insulated handle. I doubt you would get much of a spark out of it.

Luke
 
Discharging a recently juiced big blue is pretty damn fun with a screw driver. It will scare the crap out of you the first time or 2. Much more exciting than discharging a monitor.
 
The circuit is such that the big blue won't hold a charge once power is removed.
 
The circuit is such that the big blue won't hold a charge once power is removed.

Is that assuming the circuit is working correctly (so it does this) or can it not fail in a way that causes the BB to hold a charge? Just curious. I don't know anything about the circuit your are describing. I just recall hearing that monitors have something similar but that part can fail and then one gets a nasty (shocking) surprise if depending on that feature. :)
 
Well it sure looked and sounded like a firecracker went off when I did it on 2 different big blue's.

Yes, these do hold a charge. But it's a far, far lower voltage than you will find on a tube.
I have even seen brand new, never used caps pop when shorted with a screwdriver. They're tested at the factory and manage to hold a charge for months. Not much of a charge but enough to get a small arc.

As far as the original question, though -- no, you do not need to discharge these before pulling. But, it is kinda fun to do it anyway.
 
Is that assuming the circuit is working correctly (so it does this) or can it not fail in a way that causes the BB to hold a charge? Just curious. I don't know anything about the circuit your are describing. I just recall hearing that monitors have something similar but that part can fail and then one gets a nasty (shocking) surprise if depending on that feature. :)

Yes, assuming the circuit is working correctly. The big blue is nothing more than a large bypass filtering capacitor that sits on the output of the AC-DC bridge rectifier and smooths out the ripple left behind by the bridge. With a load on the output (board plugged in), when power is turned off, all the charge from the cap should travel to ground. If everything is disconnected and there's no load on the output, it's possible the cap could hold a charge. But then there might be shunt resistors in place to prevent this.

I know the dummy load on monitor chassis work differently, although there are similar shunting circuits that discharge the dummy cap upon power-down. If the shunting circuit is damaged, then you get a nice little charge waiting to discharge across your fingers! Ouch! :p
 
Yes, assuming the circuit is working correctly. The big blue is nothing more than a large bypass filtering capacitor that sits on the output of the AC-DC bridge rectifier and smooths out the ripple left behind by the bridge. With a load on the output (board plugged in), when power is turned off, all the charge from the cap should travel to ground. If everything is disconnected and there's no load on the output, it's possible the cap could hold a charge. But then there might be shunt resistors in place to prevent this.

I know the dummy load on monitor chassis work differently, although there are similar shunting circuits that discharge the dummy cap upon power-down. If the shunting circuit is damaged, then you get a nice little charge waiting to discharge across your fingers! Ouch! :p

Thanks for the explanation on the BB discharge circuit. I was not aware of that. :)

I have gotten a little zap from the chassis caps before - it is quite a surprise. Now I just am more aware of it.
 
Well it sure looked and sounded like a firecracker went off when I did it on 2 different big blue's.

I can say for a fact.....if the harness is unplugged (basically isolating the transformer assembly), big blue will keep a descent charge for quite some time.

Edward
 
From my experience, as long as you dont remove it right after its been powered on there shouldnt be any charge on it. It probably bleeds off through the transformer windings.
Its still not a bad idea to discharge it just to be sure.
 
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