'The capacitors exploded, showering the lab in flaming confetti' Welcome to the very first edition of “Who, me?” a new Reg column we hope will prove as entertaining as our Friday On-Call tales of tech support gigs gone wrong. In Who, me? we’ll celebrate the times techies stuffed up, the lessons learned and the career consequences. To kick things off, meet “Alvin”, who “In the early '90s …
And that's why the first thing my A Level Physics tutor told me to forget everything I had learnt at GCSE because it was either a lie or an over simplification.
I was then told exactly the same thing at degree level, seems a perverse way to teach to simplify things to the point they are factually incorrect and then have to "correct" that knowledge at a later date.
I don't think that I was that unusual as a 15-16 year old that I could understand that there would be shades of grey in the answer to a question. The fact that "Few kids are interested in why it's changed" is wrong on many levels;
a) The voltage has never changed, just the way it's described and for political reasons.
b) Your implying that we shouldn't teach kids anything they're not interested in
Using the new description of 230v +10% -6% or the old one of 240v +/-6%. Gives a range of valid answers and in both cases either 230v or 240v is a perfectly correct answer.
A system that marks a student down when they have given a perfectly correct answer just because they haven't given the answer the examiner was expecting is broken and not fit for purpose.
Reminds me of the quote from my boss in my first true engineering job, "Those that can do, those that can't teach...."
"... And that's why the first thing my A Level Physics tutor told me to forget everything I had learnt at GCSE because it was either a lie or an over simplification.
I was then told exactly the same thing at degree level, seems a perverse way to teach to simplify things to the point they are factually incorrect and then have to "correct" that knowledge at a later date. ..."
One of our degree lecturers said it thus: "We teach you by diminishing deceptions" .
I thought it was fair enough, *if made explicit*, for e.g. starting with Newton, which is practicable enough for some purposes, before moving on to Einstein.
With you on pointless, ambiguous or not-even-right-or-wrong questions ;-)
"I teach physics, and one common GCSE question is "What is the mains voltage?" The "correct" answer is 230V, if you write 240V you'll lose the mark. Few kids are interested in why it's changed, so I just warn them to ignore their parents if they use the "wrong" value."
Is that a 'Physics' question these days ? ... and there was I trying to be open-minded about the dumbing-down of exams ...
"I teach physics, and one common GCSE question is "What is the mains voltage?" The "correct" answer is 230V, if you write 240V you'll lose the mark."
Tell that to Northern Powergen. When they retired our original 1954 single phase 25kVa pole mounted 400v to 250v step-down transformer back in 2014 they replaced it with a 100kVa three phase (only 2 phases in use) step down transformer and used the normal tap (250v). So for me up here in Northumberland, the correct answer is 250v (presently reading 242v as it's 6pm and all the neighbours are making tea.
Hmmm. I thought there was a problem with this.
"In a DC circuit, the power consumed is simply the product of the DC voltage times the DC current, given in watts. However, for AC circuits with reactance we have to calculate the power consumed differently."
The example given finds 240v x 5 amps = 205 ish watts so there is a BIG difference.
https://www.electronics-tutorials.ws/accircuits/power-in-ac-circuits.html
Phew, it's a long time since I did this stuff and I still prefer DC.
PP
The one with the MRGC in the pocket.
My team (it wasm't me, gov, honest) blew up a Vax 11/780 not once, not twice, not even three times, but at least 5 times. Digital were confused as to why the unibus terminal interface could keep blowing up. But as it was under warranty, they kept replacing it.
It was only by chance that I was in the lab one day. Normally, they didn't let us office types in there in case we did something silly and blew up the lab (very probably the case). The lab was connected to the computer by a long length of shielded cable strung between the two building. It seems the guys in the lab had removed the earth wire from a 4 way extension lead because the earth was interfering with the oscilloscopes, and they needed to allow the earth to float high. Then the plugged their terminal in to this, to record results in the database.
So the terminal floated high (that was the days of CRT terminals, lots of high voltage there).
So the lines to the VAX floated high. And then it all earthed through the Vax. Blew the Vax up. But the lab didn't know. So they repeated their tests, blithely unaware that they had taken out a very expensive piece of kit.
When we found out, we had them label the extension lead with "UNEARTHED - NOT FOR COMPUTER EQUIPMENT", which they should have done anyway, but hey, they are boffins, the brights guys in the room , right?
We decided that we weren't going to tell DEC in case they stuck a bill for failed VAX's on to us!
We let the smoke out of a bunch of lab equipment, many times. I was working at a company that supplied equipment for airplanes, which run at 120V, 400 Hz, and we would have to run our checks from a PC connected by a serial line (120V 60Hz).
To save money on the 400 Hz system they did not tie the grounds together, and you can imagine what happened. Plug the device under test into 120V 400Hz, then connect the serial port to the device, and nothing would work. Blown serial port. We got really good a replacing plug-in serial boards, because we blew them out so often. Maybe once or twice we would blow a power supply, or in those days pop a fuse. the one 400 Hz power outlet gained a huge note "FLOATING GROUND".
Puts me in mind of the unfortunate young techie who was filling in for me when our stateside supplier sent a demo unit (in a PC) for an upcoming exhibition here in Blighty.
No one told him he'd have to flip the switch from 110v to 220-240v.
Flew across the lab he did.
I think we were all young techies when we learnt those kinds of lessons. PP
> There's nothing in PC, modern or 30 years old, that could have caused this.
Speaking as one who, in the early 90s, had to install am internal modem (those plastic-encased jobs) in a tower system under a desk, switched on the PC following the rule never to close the case immediately after installing something, because cockily closing the case straight away means it's guaranteed not to work, and saw a large spark emanate from said modem, followed by a definite conflagration, I would say your confidence in equipment and power supplies of 30 years ago is somewhat misplaced.
I did discover that it is possible to leap from under a desk straight to the wall-mounted fire extinguisher and back under the desk in two easy bounds. But after this episode, I never used internal modems again.
How about you explain me how short circuit inside 5V powered chip caused "power surge".
Simple.
Switching PSUs take their reference feedback from their most relevant output voltage, in most cases the +5V rail. Load that rail heavily and you'll see the other output voltages go up. Do something silly with the +5V rail, like that chip blowing, and you could well have the PSU go nuts. And given the crap which even today is sold as computer power supplies, never mind 30 years back, I wouldn't bet on some random PSU shutting down in a decent manner without any malodorous and/or acoustic side effects in case of a sudden overload.
And saying "that's not supposed to happen" will just show that you know shit about designing and building electronics, especially where shaving the last microrenminbi off the BoM is concerned
Putting voltage on the Ground plane does.... interesting things to computers.
I trashed my old Commodore 128 by putting 9VAC on the ground plane for the CMOS and TTL logic chips, and blew most of them. How did I do this? By putting a RS232 converter on the expansion port upside down....
And then there's the time that one of the clients for a company I was working for had an electrician who managed to put 208 on the neutral line and blew up (flames and everything!) two brand new computers. Fortunately for the client, the server was on a UPS which merely went into isolation when it saw voltage where voltage ought not to be...
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"There's nothing in PC, modern or 30 years old, that could have caused this".
You obviously haven't encountered DIY PC's built by the institution itself, or dodgy kit that was foisted on it by a senior academic with a mate who builds computers, and who somehow managed to get himself appointed as exclusive supplier.
In a previous job, I encountered both - cruddy machines supplied by a nearby university's "Microcomputer Unit" and death-traps built on the cheap by a friend of an academic.
Think of "Deadly Binders Inc." and you get the general idea. Flames shooting out of power supplies, cables overheating, and the old, old favourite, razor-sharp edges on cases. If you timed it right, the fire would cauterise your wounds.
Everything's funnier with flames. Even the word "flames" is funny.
From my own Grand Prix Des Idiots Blithering:
In the pursuit of Science I attached a lit cigar to the hose of a working Electrolux cylinder vacuum cleaner. The glowing core of the cigar burned down the wrapper in a fraction of a second, disappeared up the hose and set fire to the dust in the bag. Flames shot out of the exhaust and singed the carpet and wallpaper, earning me a damn good thrashing when dad got home.
Now tell me that you didn't start laughing at the "flames shot out" part. Without the flames it isn't funny.
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I attached a lit cigar to the hose of a working Electrolux cylinder vacuum cleaner.
I know someone who tried to de-odourize a vacuum cleaner by spraying air freshner into the hose while it was running. When the butane propellant reached the motor brushes there was a load 'pop', flames, and a spontaneous diassembly of the dust bug & contents.
Having had to deal with a SCSI ribbon cable catching fire when plugged in to the motherboard, and having seen motherboards fry because someone plugged a dodgy card in to them (even a perfectly healthy card plugged in incorrectly can blow a motherboard), I would tend to disagrree. Regarding the hard drive, it's also entire possibly that a faulty motherboard could take that out. All it would take is for the drive interface (be it SCSI, SATA or IDE) to wack a voltage up the wrong wire, and it could easily fry the drive electronics..
It has been a long time since I dabbled with (very simple) breadboard designs, so I won't comment on that aspect.
However, about 15 years ago, there was a loud "pop" (or maybe "bang") from my computer that was standing on my desk, with black smoke emanating from its floppy drive. I unplugged it and we evacuated the room. After only a few hours of venting out the room, the smell of burning electronics was nearly gone and we felt reasonably safe to resume operation. My little 3.5" floppy drive however was clearly pining for the fjords. IIRC we replaced the PSU and ditched the floppy drive, and my PC was operational again (I do not remember exactly what we had to replace, but we were operating on a tight budget and I do not think we would have forked out for a brand new computer)
My point is that if the standard components found in PCs at the time, could do all that relatively unprovoked, then I have no problems believing things could turn really ugly if you poke the monster's eye with a sharp stick.
Besides, computers are scary. There are tons of documentaries on this subject: "War games", "Terminator" (1 through 4) and The Fly.
came about because, although the W2000 installation CD had a visible hairline crack, it hadn't, hitherto, inhibited successful installation.
However, this day, the cd span at ever higher speed, with a juddering overtone. The volume of speeding cd drive and juddering rose until there was a shockingly loud noise like a gunshot, and suddenly the room was filled with pungent dust. The installation CD was history, and so was the drive. PC perfectly happy.
It being far in the past, I can now confess that, in a Nuffield A-Level Physics lesson using a bunch of plastic encased electronics modules, I connected the largest electrolytic I could find across the bench supply as a smoothing capacitor, with the polarity 'accidentally' reversed. It was quite spectacular.
Sorry Mr. Leggett...
There was the student on the lab bench opposite mine, who wasn't aware of what the ridge and the '+' markings on an electrolytic cap were meant to convey. With the working voltage for the circuit being 150VDC, for reasons I can't remember any more (no, it didn't involve vacuum tubes). So, a couple of seconds after powering on, there was an almighty bang, a rather pungent, acrid smell and a very pale student.
ectel Sorry Mr. Leggett...
Was that Headingham School?
Those who remember a certain Mr Fisher teaching Physics at the Kings School Chester circa 1990 will be chuckling at this point.
1) Teachers shouldn't fiddle absent-mindedly with large capacitors while teaching,
2) certainly not ones that have been charged from the bench 12v supply,
3) and when the inevitable happens and the fly leads make (loud, sparky, shocky) contact, said teacher should have the presence of mind not to say "FUCK" very loudly in front of 25 wide-eyed, innocent and hitherto uncorrupted boys who had of course NEVER heard such naughty words before or used them.
"Tiny diodes, when connected straight across mains, tend to disintegrate with nice light effects. Who knew?"
Works best with glass encapsulated germanium ones. At least that's what "a friend" told me.
Apparently, a pencil lead from those propelling pencils that use full standard pencil sized leads rather than the short skinny ones, when layed across the terminals of a Scalextric transformer soon start to glow and emit the most horrendous smelling fumes. Again, as told by "a friend".
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