> I recall in 7th grade, I used to bring a bag of little radial ceramic cap= acitors and > a 90V battery to class. I would charge them up, then slip them into my > classmates clothing, like down their collars. When they would later move= , > they would get a little shock from the cap leads contacting their neck, a= nd > would let out a yelp. Of course the teacher would scold these puzzled ki= ds. During my time as an electronics apprentice, the factory I worked at assemb= led stereo amplifiers which used a 40V 220uF capacitor as the bootstrap cap= acitor in the output stage. The supplied capacitors were made by Philips, w= ho were one of the few major component suppliers in NZ at that stage. However we had some apprentices who were of a wicked mind-set, who realised= that the 8uF 350V Philips capacitors used in the high voltage inverter of = the marine radios we made were the same case size, and if you didn't notice= that the blue sleeve on it was a little paler than the other capacitors yo= u wouldn't notice the difference in a box of them, especially as the box te= nded to be at the back of the bench. So a pair of apprentices would charge = an 8u 350V cap to around 500V using the insulation tester, then one would c= ome and talk to one of the women assembling the PCBs for the amplifiers and= distract them while a second apprentice would come and drop the charged ca= pacitor in the box of capacitors she was fitting to the PCBs. Inevitably at= some point the charged capacitor would be handled with resulting shock. Af= ter this happened a couple of times the women on the assembly line got very= wary of any apprentice coming and talking to them, and would carefully loo= k through thei! r box of capacitors looking for any that were different. Russell earlier said ... > Tantalums are generally more fun. > The best I've seen made a foul smell for a while (source then unknown), > then smoked profusely, then started shrieking, a jet of flame was added a= nd > then it exploded competently. >=20 > A large capacity (I think) Tantalum in a DEC PDP11 power supply had a me= tal > case. A hole was blown in the side near one end and a ball of metal rolle= d > freely along the interior and was just too large to exist the hole. This would have been a wet tantalum by the sound of it. I may have written both the following stories in the past, but they bear re= peating as warnings. But a colleague had an almost life changing with a tantalum exploding. We h= ad a new printer come in from our OEM and it was dead on arrival. So collea= gue pulled the back panel off and pulled the PCB assembly out. All the wiri= ng to the motors and print heads was long enough to allow this to happen an= d leave everything operational while testing and fault finding. He had the = power on and was bending over looking at the PCB when a teardrop tantalum w= hizzed past his ear, having launched itself off the PCB. It was in a circui= t that had switching regulators that allowed around 30V to the stepper moto= rs while running but dropped it down to about 5V to limit the holding curre= nt while the motors weren't turning. I suspect the cap was put into circuit= backwards and lasted long enough to get through final test at the factory = but having had reverse voltage on it died during transit. Finally getting v= oltage on it again it became a little rocket that left its leads in the PCB= .. Colleague wa! s lucky he didn't lose an eye. But the other capacitor incident I remember was when we had a new minicompu= ter delivered to run in the companies bureau for customer use. No-one was q= uite ready for it so we left it running a memory test as a burn in exercise= .. The card cage had about 20 slots but there was only the processor, memory= , disk interface, tape interface and one I/O card, but the power supply was= a 5V 300A switch mode to handle the potential fully loaded card cage. I ha= d my pager go off with a call that the new machine was "on fire". By the ti= me I had reached the bureau the machine had been turned off, but the descri= ption of smoke coming out the ventilation at the top of the rack seemed a b= it over the top ... Investigation showed that a 100n ceramic capacitor had decided it want a ge= nder change into a resistor - as ceramic caps are well known for doing, not= so much these days, but quite common in the past. The power supply had sai= d 'you want to be a resistor, I can supply all the current you want'. The r= esult was a charred hole in the PCB about 1.5" diameter. However there was = a problem - we had purchased the machine with minimum memory fitted and the= n added memory chips as this gave us the full card capacity much cheaper th= an buying it fully populated, so we couldn't return the card under warranty= .. The upshot was that someone (not me) was given the job of fixing it which= he did by filling the charred hole with epoxy that using Inforex wire to r= emake the connection (anyone else here deal with Inforex key to disk/tape s= ystems in the past?). The inforex wire is like fine enamelled wire wrap wir= e. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .