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Standard User camieabz
(sensei) Mon 31-Dec-12 01:26:09
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That acrid electrical burning smell


[link to this post]
 
The one that catches in your throat and sticks in your sinuses for a day or so.

It started last night, and I immediately put the PC into sleep mode, so it and the monitor power down. The top of the monitor was quite hot, and easy to reach out and touch, so that was the first suspect. I never pay attention to monitor heat though.

I also have a new router, and it's the only piece of kit that's new here, so it too is a suspect. It sits on top/front of the tower.

So I switch off the monitor completely, and power up the PC. And there's that burning smell again. Not the monitor and probably not the router. Power off quick, as the smell is burning metal and plastic now, and it's getting quite thick and worrying.

Open up the case, and unfortunately the mosfets on my mobo are covered with a heatsink (joined to the Northbridge heatsink by a heatpipe). I can't see the mosfets without popping the spring-loaded gromets on both.

[censored]

Is it the PSU? The mosfets are two inches below the PSU, so I can't tell. OK...assume it's the PSU, pull it and inspect it. No obvious damage, leakage or anything that looks untoward, but it and every other piece of kit in the tower is reeking of the burning smell.

[censored] (it's probably the mosfets)

So given the choices of:

1. Probably the mosfets and any more power to them will blow the mobo and lose the system

2. Probably not the PSU, but it might be, so replace it and see

[censored] Option 2 it is.

Thank God! New PSU and no smell. phew! smile

So that's an OCZ Stealthxstream 700w been running since March 2009. Probably on 90% of the time, and not in sleep mode or off. So at 3.5 years of say 24/7 times 90%, that maybe amounts to 2-4 times the usage of business or some home users. Can we estimate 7-14 years equivalent?

Also bear in mind that it's a 20% overclock system, I'm not too down-hearted, especially as it's not the mobo. Bought a 750w OCZ today from PC World, or would have to wait until the 3rd or 4th to find out if it was the PSU. I had an old 480w one, but didn't dare.

So that's my little bit of panic/excitement for 2012 over. grin (I hope...)

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.
Standard User Alex1M6
(regular) Mon 31-Dec-12 07:35:56
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
We had a similar issue not too long ago with a burning/fish smell coming from the landing area of upstairs. It turned out to be an electrolytic capacitor inside of a CFL light-bulb that had gone bad and was giving off the smell.

Looking at the inside of that power supply the main filter capacitor for the rectified mains appears to be located right next to two large heatsinks, so it could have been slowly cooked over those years of heavy use ( :
Standard User eckiedoo
(regular) Mon 31-Dec-12 08:18:36
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Re: That acrid electrical burning smell


[re: Alex1M6] [link to this post]
 
I often wonder how many realise that in the bases of the CFLs, there are those HF Oscillator circuits, to drive the actual Compact Fluorescent Tubes.

Much has been said about the trace of Mercury that is required to produce the UV light, which is converted to the Visible Spectrum by the Rare Earth white powders coating the interior surface of all Fluorescent Tubes, both CFLs and traditional, whether straight or curved as seen in signs.

The CFL HF circuits contain the mix of components needed to form an Oscillator circuit, eg Capacitors as mentioned (both Electrolytic and others), Toroids and Transformers on Ferrite Cores, Semi-Conductors, PCB etc.

The Electrolytic Capacitors in turn contain Alkalis, which can cause chemical burns.

Yes, most of those hazards apply to Electronic Equipment generally; but CFLs are frequently in locations where children can readily access them.

In most CFL, HF Oscillators, there is a total of 26 discrete components, as well as the hefty plastic moulding forming the Base.

I wonder how much of that circuitry is recyclable?


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Standard User Alex1M6
(regular) Mon 31-Dec-12 08:49:32
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
In reply to a post by eckiedoo:
I often wonder how many realise that in the bases of the CFLs, there are those HF Oscillator circuits, to drive the actual Compact Fluorescent Tubes.

Much has been said about the trace of Mercury that is required to produce the UV light, which is converted to the Visible Spectrum by the Rare Earth white powders coating the interior surface of all Fluorescent Tubes, both CFLs and traditional, whether straight or curved as seen in signs.

The CFL HF circuits contain the mix of components needed to form an Oscillator circuit, eg Capacitors as mentioned (both Electrolytic and others), Toroids and Transformers on Ferrite Cores, Semi-Conductors, PCB etc.

The Electrolytic Capacitors in turn contain Alkalis, which can cause chemical burns.

Yes, most of those hazards apply to Electronic Equipment generally; but CFLs are frequently in locations where children can readily access them.

In most CFL, HF Oscillators, there is a total of 26 discrete components, as well as the hefty plastic moulding forming the Base.

I wonder how much of that circuitry is recyclable?


Personally if I come across an electrical device that has a problem I like to reverse engineer the thing and see if I can fix it. Its always a treat if I need to use my oscilloscope to track down a fault on a misbehaving circuit.

If it turns out the device is not economical to fix then I usually strip the board for the various components (capacitors I will check with an ESR meter first).

I once was designing a switched mode power supply for the education of it and made the silly mistake of connecting the rectified mains filter capacitor in reverse. I observed it puffing out before the top blow off in a vicious spark filled explosion.

Luckily I was not looking directly at it as I had my eyes fixed on the oscilloscope to check the waveforms of the MOSFET (it was using flyback topology so controlling the turn off spike from the leakage inductance of the primary coil was important).
Standard User eckiedoo
(regular) Mon 31-Dec-12 11:05:28
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Re: That acrid electrical burning smell


[re: Alex1M6] [link to this post]
 
A colleague many years back, also reversed the connections to an electrolytic capacitor of the period, probably 16 to 32 MFds, 300V DC.

Probably bout 1.5 inches diameter by six inches tall, say 37.5 mm diameter by 150 mm tall.

Large enough to be potentially lethal.

It exploded directly in front of him, as he switched mains power on.

The contents, rolled aluminium foil, separators, corrosive alkaline electrolyte etc, headed upwards at high speed to splatter on the laboratory roof, about 25 feet (8 metres) above


The resulting damage, splatter etc was there for many years, being pointed out as a salutary warning, "tae mak siccer, afore switching on".


By sheer coincidence, his name was highly appropriate to the event!
Standard User camieabz
(sensei) Mon 31-Dec-12 12:52:20
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
Well I've been over the old PSU with several toothcombs and can't see an obvious issue.

There's a little wire melting in pic 4 (black wire behind the top coil), but said wire has been against the copper coil for 3.5 years, so that's pretty likely I would say. The whole thing was pretty dusty inside. Maybe the heat built up beyond the dissipation efficiency (or whatever the correct terminology is).

Pic 1
Pic 2
Pic 3
Pic 4
Pic 5
Pic 6
Pic 7
Pic 8

I would rather see a big blackened mess, so I could be sure.

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.
Standard User Alex1M6
(regular) Mon 31-Dec-12 13:34:11
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
That inductors core looks like it has been getting very hot as it looks pretty discoloured.

Edit I just googled "OCZ Stealthxstream 700w smell" and there are lots of forum posts relating to this issue. I will keep digging ( :

Just a thought but perhaps it could well be related to some other electronics, as inductors just don't start to saturate and get hot after running fine. But then again if was related to the primary drive circuitry then the main switching transformer would exhibit problems too.

Its a coupled choke that carrys the high current +12, +5 and +3.3v rails and is normally used to help smooth out the supply.


Hmm...Perhaps its related to the mixture the inductor was made out of.

Another Edit: Please be careful when poking around inside of the PSU. Its unlikely but there is a small chance that there is still a charge stored inside of capacitors on the rectified mains side, and those heatsinks can be electronically connected to various points in the circuit.

Plus the metal case is referenced to earth internally so try and keep it to using only one hand unless you are sure that everything is discharged. Take it from me, 325v across your chest really sucks.

Edited by Alex1M6 (Mon 31-Dec-12 14:28:48)

Standard User JimmyBoy
(committed) Mon 31-Dec-12 13:41:08
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
In reply to a post by camieabz:
There's a little wire melting in pic 4 (black wire behind the top coil)...

Nice pictures!

That coil appears to have received a good 'burning'. It's probably in the 3V3, 5V or 12V output (whichever output has the highest current rating).
If you move the output cabling from the PSU chassis, you may find the culprit underneath the cabling - look for the smoke trail/two legs (with charcoal or an air gap between them) or a damaged electrolytic capacitor. Also check the underside of the circuit board.

EDIT: Picture 6 appears to have captured the damage - zoom in to the base of the coil/inductor - the windings appear to be scorched. The damage should be visible on the underside of the PCB.

__________________________________________
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Edited by JimmyBoy (Mon 31-Dec-12 14:12:29)

Standard User Alex1M6
(regular) Mon 31-Dec-12 14:25:51
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
Read this, it pretty much sums it up LINK

According to this the inductor gets very hot and slowly cooks/begins to melt everything close to it.

Edited by Alex1M6 (Mon 31-Dec-12 14:30:26)

Standard User eckiedoo
(regular) Mon 31-Dec-12 14:37:59
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
More than half-a-century back, I was asked to repair a neighbour's radio.

Typical 1930's model, valves/tubes, mains dropper etc, in a relatively large cabinet to allow cooling air to circulate.

On taking the fretted back off, I was confronted by a mass of loose felt or fragments of thread that had gathered inside, rather like the contents of a vacuum cleaner bag, used mainly on carpets, apart from where it had been singed by the mains dropper.

Several handfuls of felt later, I started to expose the valves etc, rather like an archaeological dig.

Yes, I did manage to repair the radio.
Standard User towdgeezer
(newbie) Mon 31-Dec-12 16:08:08
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
In reply to a post by eckiedoo:
A colleague many years back, also reversed the connections to an electrolytic capacitor of the period, probably 16 to 32 MFds, 300V DC.

Probably bout 1.5 inches diameter by six inches tall, say 37.5 mm diameter by 150 mm tall.

Large enough to be potentially lethal.

It exploded directly in front of him, as he switched mains power on.

The contents, rolled aluminium foil, separators, corrosive alkaline electrolyte etc, headed upwards at high speed to splatter on the laboratory roof, about 25 feet (8 metres) above


The resulting damage, splatter etc was there for many years, being pointed out as a salutary warning, "tae mak siccer, afore switching on".


By sheer coincidence, his name was highly appropriate to the event!

I well remember an incident that happened to a pal and myself when we were attempting to grind away the rear forks of a cycle frame for some reason that escapes me fifty years later.
We were using his fathers home made grinding machine which comprised an unguarded 9" wheel mounted on a 3/4 HP single phase electric motor.
Mounted on the top of the motor in a sealed steel cylinder was a bi-polar electrolytic capacitor used for stating the motor. It was cut out of circuit by a centrifugal switch when the motor reached full revs.
I should mention that the grinder was located in a damp poorly lit cellar.
Unfortunately my mate applied a bit too much pressure to the wheel and the motor stalled.
Immediately there was a terrific flash and bang, followed milliseconds later by something whistling around the cellar bouncing off all the walls.
Somewhere along the way it took out the single light bulb and we were left in darkness terrified to move in case what seemed like miles of aluminium foil that we saw for a moment before the light went out, were still alive. Examination afterwards showed that the foils had disconnected when the thing blew up.
His father was not amused.
Standard User camieabz
(sensei) Mon 31-Dec-12 16:22:16
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Re: That acrid electrical burning smell


[re: Alex1M6] [link to this post]
 
In reply to a post by Alex1M6:
That inductors core looks like it has been getting very hot as it looks pretty discoloured.


I noticed the discolouring, but guessed it might be normal wear and tear, given the heat that builds up in these things. Up close, it looks a little like a tiny amount of liquid has touched it and dried it. Paint melted off maybe? (I notice the others are green)

In reply to a post by Alex1M6:
Its a coupled choke that carrys the high current +12, +5 and +3.3v rails and is normally used to help smooth out the supply.


Yep, they reduce 'noise' or jitter on the rails. Or that was my interpretation. Frankly, I've never been inclined to poke around inside PSUs for the simple reason that you state later on

In reply to a post by Alex1M6:
Another Edit: Please be careful when poking around inside of the PSU. Its unlikely but there is a small chance that there is still a charge stored inside of capacitors on the rectified mains side, and those heatsinks can be electronically connected to various points in the circuit.


Yep, I know. Once switched off, I flicked the off switch on the PSU, left it for an hour or so then popped the mains cable.

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.
Standard User camieabz
(sensei) Mon 31-Dec-12 16:46:41
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Re: That acrid electrical burning smell


[re: JimmyBoy] [link to this post]
 
In reply to a post by JimmyBoy:
Nice pictures!


Ta! Just got the camera for my crimbo. First use...PC parts. wink

In reply to a post by JimmyBoy:
That coil appears to have received a good 'burning'. It's probably in the 3V3, 5V or 12V output (whichever output has the highest current rating).
If you move the output cabling from the PSU chassis, you may find the culprit underneath the cabling - look for the smoke trail/two legs (with charcoal or an air gap between them) or a damaged electrolytic capacitor. Also check the underside of the circuit board.


I'll probably get round to it in a week or so. Want to let the new PSU get a few days of use, juts to make sure. Assuming it is the PSU, and I'm 99% sure it is now, I'll cut off all the good wiring and tie-wraps to see what we can see. More pics to follow!

In reply to a post by JimmyBoy:
EDIT: Picture 6 appears to have captured the damage - zoom in to the base of the coil/inductor - the windings appear to be scorched. The damage should be visible on the underside of the PCB.


You had me going for a second when I revisited that pic, but alas it is not what you think. See:

Pic 9
Pic 10
Pic 11

See the thinner wrap of copper around the coil? It appears that once said wire exits the coil it gets black sheathing. The black thing in the background is a sheathed capacitor. At this level of detail my zoom/flash/focus/handshake issues are getting noticeable. Not to mention the dust. smile

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.
Standard User camieabz
(sensei) Mon 31-Dec-12 17:03:04
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Re: That acrid electrical burning smell


[re: towdgeezer] [link to this post]
 
Good stories.

Was Googling for 'PSU electric shock' and came across a few funnies:

http://www.tomshardware.co.uk/forum/329620-10-shocke...

Got shocked by a PSU heatsink. Will I explode?


No you won't explode but 2 things can happen:
->the electric current will force cell division which can lead to some extra limbs OR
->your body will become one with the PSU and you will become....the chosen one


Due to the increased electrons in your body because of the shock you will most likely notice your head increasing in size. This is known as Bloaty Head syndrome. You will need to go to the hospital were the doctors can literally pop your swollen head and then pump it back up to the correct PSI.


So you were actually dumb enough to open a plugged in power supply and touch the inside?

Wow, there's one born every minute.


death by electrocution is instant (or near instant), so you are fine.


laugh


However, none of these tell me how long a PSU can retain a charge. I assumed an hour with the PSU switch off to be able to open the casing without serous risk, and as long as I didn't poke around inside with a wet finger I should be ok. ooo

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.
Standard User eckiedoo
(regular) Mon 31-Dec-12 17:36:15
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
If The charged capacitor is completely isolated and has a very high inter-electrode resistance approaching infinity, then the charge could remain for years, rather like the aircraft crashed during WW2 in Greenland, when found relatively recently, with tyre pressures close to normal.

However in typical circuitry, the load such as the (rest of the) computer will tend to discharge those supply capacitors to a safe level quite quickly.

When dealing with EHT capacitors (25 KV typically), we generally used a "Brinkley stick" to discharge them.

This was a metal hook, mounted on an insulating handle, with a wire to chassis or earth.

Brinkley was the one-armed boatman who ferried early radar developers over the river short-cut to one of the early radar stations. His missing arm was replaced by a hook, "Long John Silver" style.
Standard User towdgeezer
(newbie) Tue 01-Jan-13 15:14:38
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
In reply to a post by eckiedoo:
If The charged capacitor is completely isolated and has a very high inter-electrode resistance approaching infinity, then the charge could remain for years, rather like the aircraft crashed during WW2 in Greenland, when found relatively recently, with tyre pressures close to normal.

However in typical circuitry, the load such as the (rest of the) computer will tend to discharge those supply capacitors to a safe level quite quickly.

When dealing with EHT capacitors (25 KV typically), we generally used a "Brinkley stick" to discharge them.

This was a metal hook, mounted on an insulating handle, with a wire to chassis or earth.

Brinkley was the one-armed boatman who ferried early radar developers over the river short-cut to one of the early radar stations. His missing arm was replaced by a hook, "Long John Silver" style.

I understand that most of the German WW2 bombs dropped on the UK were electrically detonated.
Paper capacitors within the fuse cartridges were charged immediately before release from the aircraft via a button on the fuse assembly.
Bomb disposal officers had to drill into the fuse and inject a liquid of a high specific resistivity to discharge the capacitors slowly but not low enough to cause the things to detonate.
Allied bombs used a chemical time delay utilising the action of acetone on acetate sheets holding back a striker pin.
I too used a "Brinkley Stick" although we didn't call it that, to discharge the high voltage capacitors within induction heating machines used to anneal the ends of small springs for clockwork timing mechanisms.
Many of these machines were built locally from surplus WW2 radar set componants.
They were potentially lethal with no safety interlocks on doors etc. They operated in the low Mhz region with powers of around 5kW (R.F.) and HT supplies of around 5kV.
One much more modern machine was found to be wiping out UHF television reception over a wide area when BBC2 started on UHF.
We were puzzled because the thing ran at 3.5 Mhz and we couldn't see how it could produce harmonics at a high enough frequency.
The machines either used a single large-water cooled or air-cooled triode valve or two valves in push-pull.
It turned out that the valve type was prone to producing spurious UHF radiation by the action of stray electrons going into very fast circular orbits within the internally finned valve anode. Rather like a klyston or magnatron.
The solution was to fasten a dirty great magnet to the outside of the valve anode to attract and keep the stray electrons, this meant extensive metal bashing to provide the necessary HV clearances.
Funny stuff RF (except when you got a burn from a work-coil).
Standard User systemx
(experienced) Tue 01-Jan-13 16:14:07
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
I'd replace all the electrolytics as a matter of course.

A new year and the central heating was on the blink, fired up on hot water but not on heating, problem is actuator motor. Thank heavens for ScrewFix Direct.

http://www.screwfix.com/p/drayton-synchronous-motor/...
Standard User camieabz
(sensei) Tue 01-Jan-13 17:12:46
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
I decided to reduce the amount of clutter in the PSU case. Just a tad mind. grin

Pic 12


This is definitely the offending component. The coil in Pic 13 next to the bad coil was half an inch from it and has no acrid smell, while the big coil still does. Note also the discolouring of the big coil, as if some liquid has dried on it.

Also notice in Pic 14 the colour of the copper [1] on the coils versus the copper on the big one. Not the 'red' copper, but the orange copper. Also the red copper at the bottom of the big coil is slightly brighter than that of the red copper higher up. Heat difference I imagine.

I thought all that black gunk inside was an obvious sign, but it seems to be there on most of the coils, albeit to a lesser degree.

Lastly, a quick peek at the underside of the PCB in Pic 15. There's little obvious burning or melting, other than normal heat marks. Any damage seen is due to my determined use of pliers and cutters.

[1] - The 'copper' in all the coils and indeed in all of the wiring I removed is not copper. It is (probably) aluminium with a copper jacket. You can see the cut off ends in Pic 14. A nice, cheap way to avoid copper costs, but is the aluminium as conductive as copper? Certainly, the ,melting point of aluminium is far less than copper, but I'm pretty sure 600+ Celcius is way above what we would see in a PSU anyway. smile

I assume the copper jacket prevents corrosion. Is it a copper jacket, or just copper coloured (or copper based) paint? See the cut end on the yellow coil in pic 13. Looks like paint.

Btw, the coil wire is solid core, while the plastic jacketed wiring within the PSU was stranded (most likely for flexibility in the PSU cables).

So that's that! I hope my PSU saga been slightly interesting.smile

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.
Moderator billford
(moderator) Tue 01-Jan-13 17:22:44
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
In reply to a post by camieabz:
A nice, cheap way to avoid copper costs, but is the aluminium as conductive as copper?
At high frequencies something called "skin effect" (Wiki) comes into play- most of the current flows in the outer layer of the conductor. So it's not too important what the "core" is made of, 'cos most of the current isn't flowing in it!

Even at mains frequencies it's enough to allow the high voltage cables on pylons to use a steel core for strength, with the current flowing in the outer layer of aluminium.

Bill
bill@thinkbroadband.com __________________Planes and Boats and ... __________________BQMs: IPv4 IPv6
The author of the above post is a thinkbroadband moderator but it does not constitute an official statement on behalf of thinkbroadband.
Standard User MHC
(sensei) Tue 01-Jan-13 21:55:24
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
In reply to a post by eckiedoo:
A colleague many years back, also reversed the connections to an electrolytic capacitor of the period, probably 16 to 32 MFds, 300V DC.

Probably bout 1.5 inches diameter by six inches tall, say 37.5 mm diameter by 150 mm tall.



I doubt it ... 1F at 300V is diffucult, 16 MF - probably impossible.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User MHC
(sensei) Tue 01-Jan-13 22:04:22
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Re: That acrid electrical burning smell


[re: camieabz] [link to this post]
 
A few years back DEC (Digital Equipment Corp) who produced the PDP and VAX ranges had a problem with their monitors.

You could turn off and unplug a monitor then four hours later touch the live and neutral pins on the mains plug and get a shock of over 400v from stored charge.


An old trick in the electronics industry was to take a small high voltage capacitor and tape the legs down on each side. Charge it up and then drop it into someone's jacket pocket ... some time later there would be the "What the ... Which one of you people with an unknown father, did that ?" scream!


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User eckiedoo
(regular) Tue 01-Jan-13 22:32:42
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Re: That acrid electrical burning smell


[re: MHC] [link to this post]
 
Agreed, I should have used the long-hand, 16 to 32 micro-Farads.

Thanks.
Standard User MHC
(sensei) Tue 01-Jan-13 22:33:51
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
or even uF ...


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User eckiedoo
(regular) Tue 01-Jan-13 23:02:04
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Re: That acrid electrical burning smell


[re: MHC] [link to this post]
 
That was around the late 1980s, as "Dumb Terminals" spread rapidly in large quantities around particularly electronics factories, for remote access to central computers such as the VAX - Virtual Architecture Extended (and its basic Timing Unit of 1 Clunk).

It applied to more than the PDP/VAX range; being mainly the VT100 and VT102 CRT Monitors - BUT it also applied to various others such as the WYSE.

The charge was from the Filter Capacitor across and built into the Mains Input Socket, which became isolated from the discharge effect of the internal circuitry when the Monitor was switched OFF using its own Mains Switch, before switching off and/or unplugging from the wall socket.

We received a Safety Warning from our Central Safety Laboratory, which in fact gave the WRONG procedure for Safe Disconnection.

Myself and a former colleague (of about 20 years previously) at another location both spotted the error, resulting in a revised version version of the Safety Warning being issued very quickly.

Later, a small suitably shaped and punched PCB with a Discharge Resistor became available to push into the fixed male receptacle on the Monitors.

The PCB had rectangular, through-plated holes which made contact with the Live and Neutral Pins in the male receptacle.

The hole for the Earth/Ground pin was not plated etc.

t was "hidden" when the cable connector was plugged in.

In fact, to our consternation, we realised that it was a problem with virtually all the similar connectors used on the equipment we designed and manufactured in substantial quantities.

Thanks for reviving the memory!
Standard User MHC
(sensei) Tue 01-Jan-13 23:29:37
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
We picked it up in late 1982 ...


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User eckiedoo
(regular) Wed 02-Jan-13 07:56:20
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Re: That acrid electrical burning smell


[re: MHC] [link to this post]
 
And it was generally when the monitors were being "picked up" to be moved, that the effect might become apparent, although I do not recollect anyone reporting such "pin-[censored]" shocks to us.

The capacitors were very small in the pica-farad range, for dealing with RF Interference.

=====================

Regarding the various smells associated with faulty, overheating equipment, how many remember the "Burnt Cabbage" smell emanating from Selenium Rectifiers?

Rotten Eggs from Ebonite insulation material, both when overheated and when being machined.

It was surprising when teaching in the RAF, how many trainees asked-
"What does burnt cabbage smell like?"

Reconstituted Dried Cabbage and Dried Potato Powder, both from Government Emergency stocks, featured regularly in the main meals of the day.
Standard User camieabz
(sensei) Thu 03-Jan-13 23:28:36
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Re: That acrid electrical burning smell


[re: eckiedoo] [link to this post]
 
The viewing of those pics maxed out my webspace allowance (first time ever).

Have deleted them, and they can now be downloaded in a .zip file via:

http://www.freefilehosting.net/psupics

~ Camieabz ~

All Connection Data ~ Some plusnet links

mod'er·a'tion n.
Synonyms: temperance, restraint, modesty.

Edited by camieabz (Thu 03-Jan-13 23:31:25)

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