Checking For Polarity

Power supply testing is something every instrument line has to do, one way or another. Some lines have come up with nifty ways of making power supply testing fast and easy. Ours is cumbersome to test, and we do it in sections or modules. Next door to us the Precision Group has a faster, much more stylin’ method for pre-testing all their power supply boards. They’ve made some custom fixtures that fit onto Hubie carts (the instrument carts we push boxes all over the shop floor on) and they drop assembled power supplies into these safety fixtures. One side of the fixture has a plexiglass door with a hinge on it. You can access the boards inside if you need to, but mainly the plexiglass is there to act as a shield just in case one of the main capacitors decides to blow up.

Normally, big electrolytic capacitors don’t just “blow up”. Sometimes they are defective, sure. But to get them to really explode you have to feed them voltage in the wrong direction. The Precision Group instruments use some rather large capacitors on their power supply motherboard. An assembler installs them to the board by putting two good sized phillips head screws through the circuit side of the board and then torques the screws down which brings the big capacitors snug to the component side of the PC board. Under each capacitor there is a hole in the board big enough to see through. What you’re looking for is a plus sign (+) to show up through those holes. If the plus sign isn’t there, you have installed the capacitor with it’s polarity reversed. That’s going to give them the juice in the wrong direction and then you get to experience some unusual things. Sights, sounds, and smells, to be more specific.

Meth is always picking on this stupid guy that works in their assembly area. He’s mentally slow and an easy target for ridicule. I don’t like talking to Stupid Guy and I try to keep my exposure to him limited to an absolute minimum. He’s got coke bottle thick lenses on his glasses and he has to wear hearing aids even though he seems to hear people just fine without them. It’s weird. Often, he refers to himself as Slut Puppy. It’s obnoxious the way he blurts out “I’m a Slut Puppy heh heh heh” to whomever is around. Anyway, he doesn’t pay attention to what he’s doing while he’s working. Many times his job on the evening shift is to build and test power supplies. He’s managed to blow up a few of ’em tonight. The first one startled me because of this sudden loud popping noise, and for a split second I thought I saw a bright blast of white light illuminating the ceiling over their product line. When I got up to investigate what had happened, I saw Stupid Guy walking around with a dumb grin on his face and he was yelling. His clothes were spattered with liquid stains of some kind and as I walked closer to him and the power supply test set I smelled a stench of burnt fish oil. He blew up one of the big capacitors. Those meaty ones really stink when they burn up.

Stupid Guy wandered around with a handful of shop towels brushing at the stains on his clothing while I took a close look at the cooked PC board inside the test fixture cart. Clear, oily liquid was blown all over inside the plexiglass shield and some of it had already seeped out onto the floor below the cart. I peeked through the hole under the largest capacitor on the board and sure enough, I saw no plus sign. He put the shit in backwards. Fool. Later on in the shift I was walking by in the hallway and I got lucky. I actually saw him blow up another one of the big caps. It was amazing, like watching a pure white light for a fraction of a second engulf Stupid Guy and the power supply test set. It was like a massive flashbulb on a vintage camera had discharged. As the light erupted from the test fixture, his shadow and the shadows of the equipment around him were cast in jet black perfectly on the ceiling above. A fine mist belched out of the test fixture and landed all over the floor. It was awesome. Well, except for the burnt fish smell.

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~ by factorypeasant on July 13, 2005.

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