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Old 5th Aug 2022, 5:19 pm   #61
avocollector
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Mine was a real classic - the mains plug on a radio clock lead needed replacing so I cut the plug off and wired a nice new mains plug onto it. But then it still did not work However then I noticed my Variac had the nice new plug on it's now shorter lead - the 2 leads looked identical!! Duh!!!
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Old 5th Aug 2022, 6:59 pm   #62
SiriusHardware
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Ever made the most beautiful, meticulous job ever of putting a DIN plug or sub-D plug on the end of a cable, only to realise that you should have slid the plug cover onto the cable first?

Me too.
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Old 5th Aug 2022, 7:12 pm   #63
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All too often!

... and it's never quite as neat the second time round.
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Old 5th Aug 2022, 7:58 pm   #64
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Originally Posted by SiriusHardware View Post
Ever made the most beautiful, meticulous job ever of putting a DIN plug or sub-D plug on the end of a cable, only to realise that you should have slid the plug cover onto the cable first?

Me too.
And you can't simply snip the cover as you could with the old rubber mains plugs!
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Old 5th Aug 2022, 8:55 pm   #65
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Quote:
However then I noticed my Variac had the nice new plug on it's now shorter lead - the 2 leads looked identical!! Duh!!!
Oh, yes! Cockpit windscreen heat switch on one of our aircraft faulty, 4 pole, 3 way switch, off, low, full - easy. New switch from stores, take all the screws out of the new switch, transfer one lead at a time from the old switch - done. Button up the panel - test - still faulty.
What's that nice bright shiny switch doing in my toolbox......
That's what happens when tea breaks interfere with work......
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Old 5th Aug 2022, 9:37 pm   #66
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Originally Posted by SiriusHardware View Post
Ever made the most beautiful, meticulous job ever of putting a DIN plug or sub-D plug on the end of a cable, only to realise that you should have slid the plug cover onto the cable first?

Me too.

WORSE !!! It was a 25 way D connector!!!!

Joe
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Old 5th Aug 2022, 10:39 pm   #67
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And you can't simply snip the cover as you could with the old rubber mains plugs!
Don't get spotted by the boss.
I did once and ended up having to fit a new non snipped plug.
Plugs never forget that they have been snipped even when fossilized.
The weed roots will find out well after the appliance is long gone
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Old 6th Aug 2022, 3:38 am   #68
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Ever made the most beautiful, meticulous job ever of putting a DIN plug or sub-D plug on the end of a cable, only to realise that you should have slid the plug cover onto the cable first?

Me too.
Err, yes.... Fortunately for D series connectors (and those nice EDAC516 things) there are back shells that come apart and which can therefore be fitted round the cable afterwards.

I have also learnt to tie a loose knot in the cable before sliding the connector shell on. Otherwise it will generally fall off the other end of the cable and roll/bounce into some dark corner of the workshop.

As an aside, if you have a cat never try to make a cable that's about the same length as the height of your workbench. If you do, when wiring one end, the other end will jiggle about near the floor and will become an instant cat toy....
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Old 6th Aug 2022, 7:47 am   #69
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WORSE !!! It was a 25 way D connector!!!!
Joe
I knew someone who managed it with a 50-way connector!
Which reminds me of another story. We used quite a lot of the 50-way connectors. They seemed quite expensive but we always accepted that if we wanted them we had to pay the price. Then one day one of the group noticed that they were much cheaper from another supplier. So he phoned the expensive supplier to complain about being ripped off. The supplier informed him politely that he had been ordering mil spec components and that if he wanted normal spec they could do them much more cheaply as well. Turned out that whoever made the original order had mistakenly ordered mil spec and for years afterwards we had just been repeating the original order.
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Old 6th Aug 2022, 5:08 pm   #70
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I used to work on X-ray machines, these went up to 150kV. The cables between the transformer and tube were about 2 inches thick and the plugs and sockets were oil filled.
The oil would start to break down after a while, the best check for this was to sniff the end of the plug. Problem was that the cable had significant capacitance and would hold a charge for a very long time. Standard procedure was to discharge the cable by holding the plug against ground.
Most engineers I worked with had a small scar on the end of their nose where they had forgotten and drew a large spark between the cable and nose.

Peter
I did something similar whilst experimenting with an old valve radio chassis. I was always careful to disconnect mains power before carrying out adjustments, but I was not so mindful of charged HT capacitors.

Leaning gradually forwards to inspect the circuitry whilst holding the chassis, my nose came closer to an exposed connection...zap! I sat up straight, smartly!
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Old 6th Aug 2022, 5:16 pm   #71
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Charge storage was always an issue with high voltage capacitors - they could have been discharged when removed from a system but unless you wired a short across the terminals the embedded charge would creep back to bite you!!!
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Old 6th Aug 2022, 5:24 pm   #72
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Not really an idiot thing to do but I recently bought a seized “John Bull” dial indicator from a steam fair that looked a nice little repair project.

It took less than 5 minutes to dismantle to component parts. Sorting out the damage only a few minutes though reassembly took nearly 2 rather frustrating days as the various parts and springs needed pre tensioning during assembly to actually work. This would have originally been assembled using quite a few jigs and fixtures which I didn’t have!!

Eventually after dozens of attempted reassembling tries, I managed to get it back together in a working state!!


Christopher Capener
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Old 6th Aug 2022, 5:28 pm   #73
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I remember when I worked in transformer testing we had some HV transformers which were coated with a special varnish a sort of red color not the normal brown anyhow it turned the HV secondary into little capacitors and I found out the hard way they held a nasty little charge I presume if the AC was tuned off near the crest of the wave it would hold the peak AC volts
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Old 6th Aug 2022, 10:09 pm   #74
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Default Re: I知 an idiot!

Quote:
Originally Posted by joebog1 View Post
Quote:
Originally Posted by SiriusHardware View Post
Ever made the most beautiful, meticulous job ever of putting a DIN plug or sub-D plug on the end of a cable, only to realise that you should have slid the plug cover onto the cable first?

Me too.

WORSE !!! It was a 25 way D connector!!!!

Joe
Been there, done that. No matter how hard you try you never seem to make as good a job of resoldering all the connections as you did the first time.

Keith
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Old 7th Aug 2022, 11:08 am   #75
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Out of interest I connected an AVO in series with the fuse to see what current it was drawing.

Surprised that it is as low as 25mA and no obvious sign of a surge at switch on, it is maybe too fast to register on the AVO.

David
In times-past one of my clients had people in over the weekend to do PAT on all their gear, which included a bunch of what were then top-end 21-inch Sun Microsystems monitors. The PAT-people looked at the stickers on the back of these monitors and, seeing that they were rated for 600 Watts, replaced the 13A fuses in the kettle-leads wiuth 3A ones.

After a few days the client was unpleased - monitors were failing at switch-on. The PAT-people had failed to account for the combined effect of a SMPS PSU capaacitor-charging current-inrush *and* the degauss-circuit activating at switch-on. I sent a couple of guys out to the local DiY sheds to buy up every 13A fuse they could find, and paid them triple-time to fit these fuses in every plug.

The PAT-testing company did _not_ get paid for their work!
Admitedly I have failed/replaced 13A fuses with 3/5A in TV's at work, although these were in line PSU's on 22" LED backlit units, so about 12V 3A, so a 13A fuse wasn't correct at all.

I've certainly done the "lead in amps to measure voltage" on mains, luckily it was in a fused 3 way adaptor and turned in remotely.
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Old 9th Aug 2022, 2:12 am   #76
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Greetings all.

I have been using this topic as a check list.
Yep! Been there. Done that!

My own contribution. Working on a HF "brick". A small self contained RF amplifier for increasing the output power of my FT817 low powered transceiver from 5 Watts to about 25 Watts.
It was working quite well into a dummy load (maybe I am the dummy) but I needed to clean up a bit of solder.
Removed the drive from the FT817 but did not remove the 12 Volt power.
OOPS!!
Used the soldering iron to make the necessary adjustment not thinking that the tip of the iron is earthed.
Exit 2 unobtanium RF power transistors.
GRRRRRRR!

Fortunately we do live and learn.

Cheers, Robert.
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Old 9th Aug 2022, 9:27 am   #77
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Don't be too embarassed guys, it's not only the EE's - even us poor chemists slip up now and again....

Mine, I spent most of my working life with air & moisture sensitive materials, so was used to vacuum systems, Nitrogen or Argon padding, dried reactants, etc., until one day I was in charge of a new Acrylate modified Polyurethane product, and specifically the production scale-up after R&D.

Anyway, I wrote all the relevant production protocols, and sent one of the guys over to Germany for the first developmental production run, thinking no more of it. A day or so later when the first run started, I suddenly had an urgent call from Germany.... "the torque on the reactor agitator's going up... and the circulation pump keeps tripping out... what do we do ?" - Errr... shut it all down, full cooling, etc. etc... and cross your fingers ?! Net result, within minutes, one reactor of solid gelled polymer. Fortunately, it was a development scale reactor, so there was only about 6MT in a 10MT vessel at that point.

My mistake - being so used to air sensitive materials, I'd simply forgotten to add an air (Oxygen) feed & purge of the reactor, to stabilise the acrylate. Without it, the reactor contents had gone into free-radical polymerisation, and effectively set solid. In the end, it took 3 contractors several days, working with water-jet cutters & breathing gear inside the reactor, to cut the polymer out.

What do they say ? **** happens
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Old 9th Aug 2022, 10:26 am   #78
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That's a more extreme example, in the 'day job' though!

And for something large and upscaling, I'd have expected an independent check and sign-off of the process before it goes 'live.'

So who's the idiot, you for a slip of memory, or the person in charge of the process for new-process implementation?
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Old 9th Aug 2022, 11:37 am   #79
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In the past I had to replace the diodes in a SMPS, but failed to remember that these diodes came in stud-anode and stud-cathode variations.

I mistakenly fitted one of each. Which doesn't work at all well in the classic bi phase full wave circuit. Hell, that power supply screamed!!!
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Old 9th Aug 2022, 11:45 am   #80
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No, that won't work. You can never blame process people. They are always quick to point out that there is no written process for doing so, therefore you can't. Neither is there a written process for writing a written process about it and so on, ad inf.

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