Author Topic: Big mistakes we or someone else did with electronics.  (Read 8607 times)

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Offline NiHaoMike

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Re: Big mistakes we or someone else did with electronics.
« Reply #25 on: June 07, 2011, 01:45:14 am »
At work, I once got a breakout board (sent back from a customer) that had a spider web of wires on the back. After a little examination, it turns out that the pinout was accidentally mirrored. While I was thinking the board designer wasn't paying attention, I later looked through a stack of paperwork from the customer (the manufacturer of the module that was meant to go on the board), and on the last page was a pinout diagram with corrections scribbled in pen. (The customer wasn't right that time!) The board was returned because it was performing very poorly, not surprising because the rework job ruined all the nice, controlled paths. That board ended up as a paperweight.

And then there's the time when someone put a chip into the socket the wrong way around and ended up melting the socket...
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Offline McPete

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Re: Big mistakes we or someone else did with electronics.
« Reply #26 on: June 07, 2011, 09:37:08 am »
I spent a few hours one day trying to make a small adjustable DC supply regulate properly- it was built by electrical fitter mechanic apprentices in the 80s, so no diagrams, and some pretty average construction... But it had "sentimental value".

 I had a rough idea of what the circuit was doing, but I couldn't for the life of me explain why the ammeter wasn't working, and the voltage regulation was playing silly buggers with me. I took careful note of a mark on the ammeter "I max" at 750mA, and was careful not to exceed that, measuring the output with my DMM.

I leant back, and asked a question to a colleague... Who walked over, grabbed the current regulation knob and cranked it out. Immediately, a large resistor caught fire, as 10A flowed from the output... The resistor had burnt a hole clean through the board, and the main transistor (an MJE3055, I think?) had gone short circuit... Needless to say, the customer was not thrilled with the report "technician error- unrepairable"...


 

Offline qno

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Offline sacherjj

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Re: Big mistakes we or someone else did with electronics.
« Reply #28 on: June 07, 2011, 01:15:53 pm »
I was working near 480V.  Some idiot on a fork lift backed into me and almost crushed me against the wall.  In trying not to die, I inadvertently got 480V across my pinky finger.  It cooked pretty well.  In about at the knuckle and out near the nail.  I have no ill effects other than a good scar at my knuckle.  But it was a while for my body to deal with the killed skin and muscle tissues.

I don't understand how people who can't operate machinery like that manage to survive. I've been fairly lucky in that I've only ever gotten a second or two of line current.

He was fired that day.  He backed into a full pallet of very light equipment and didn't see me behind the pallet.  I was real luck there.  

One of the coolest screw ups I had as a kid learning electronics, many decades ago, was hooking up a 555 wrong.  I believe it was either an off by one error on a pin on the breadboard or a rotated chip.  I don't remember which.  But the whole setup got really hot, really fast.  I was using bare wire for short jumpers and I pulled out a jumper and left a jumpered shaped burn between my finger and thumb.  The chip melted my breadboard really well underneath it.  The holes would now only take DIP width pins, as they were molded to the chip leads.  I remember being amazed that the old 555 took the abuse and still worked fine.  And I cooked the crap out of it.  :)
« Last Edit: June 07, 2011, 01:23:03 pm by sacherjj »
 


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