Expect the unexpected

[Biggles]

A few years ago I made a nixie tube clock and it has worked perfectly until the other day, when I noticed it was off. I naturally assumed it had been unplugged by mistake but this wasn't the case. As the pcb is visible through the clear plastic cover I had a close look and noticed a large caterpillar was inside lying across the mains bridge rectifier. The fusible protection resistor was fried and the caterpillar had a burn mark on it. The unit is completely sealed apart from a tiny hole where the neon bulb for the flashing colon pokes through. It looked too small for the caterpillar to squeeze through but this was the only possible entry point. I was more than a bit surprised to see the caterpillar and wonder what kind of flash there was when it was electrocuted. Good job the fuse resistor was in circuit. A truly bizarre fault.
Alan.

[turretslug]

A whole new meaning for "creeping failure".

I heard a report the other day about a tropical(?) species of ant that is attracted to electric fields and is becoming established in Britain- the worry being that they will congregate in consumer units, junction boxes, switchgear and so on and lead to malfunction or even fires. I don't think it was a wind-up Perhaps some caterpillars have similar inclination.

[Phil G4SPZ]

'Expect the unexpected' is indeed a good maxim. Whilst not having encountered caterpillars in electronic equipment, I did have to investigate a spate of false alarms from ionization-type smoke detectors in the 1980s and found the cause to be tiny insects called thrips or 'thunderbugs' which seemed keen to crawl inside the ionisation chambers.

More commonly, I have been presented with faults having two simultaneous causes, and this happens far more often than pure chance would suggest. One of the oddest was the loss of both dipped headlights on my car. Having wasted much time checking common factors such as fuses, switches and wiring, I discovered that both bulbs' dipped beam filaments had failed at the same time.

[MrElectronicman]

I had something similar happen a couple of years ago.

I had a DTV converter sitting on my work bench, and I came down the next morning to start work on it, only to find that hundred of ants were running all over it. When I opened the cover they appeared to be congregating in the RF module. The unit was not connected to the mains at the time, but there was something in the RF unit that was attracting them.

[turretslug]

Got it- "electric fire ants"- the "fire" bit being the intensely stinging bite, rather than propensity for heating appliance immolation.

As a trainee, I once made up an computer-to-monitor interface/level shifting box with DC-coupled BCY71s and BC109s (what was in stores). Being a clever-dick, I made it as compact, hence difficult to work on as possible- it couldn't fail to work, could it? Red and green outputs were fine, blue was inverted and clipped. I measured around and quickly came to the firm conclusion that the "BC109" concerned had a PNP chip lurking within- ridiculous, of course, but that was what the circuit voltages pointed to. My supervisor smiled wanly and said, "I don't think so..." Oh, alright, I know what he actually means- I'm incompetent, an idiot and a fantasist to boot.

I was on leave subsequently, someone whose knowledge and competence were beyond dispute got to work on it and sure enough- a PNP BC109!

I still find it hard not to check new, reputable source transistors before I use them...

[Skywave]

Several years ago I had a small PC in the 'garage'/workshop. One day, the computer wouldn't power up. An inspection revealed that its mains lead had been severed - not totally, but the inner brown / live wire had been cut through. I also found that the mouse lead was totally severed. Although at quite a loss to understand all that, I made the necessary repairs, but subsequently discovered - by careful observation - that the cause was our pet rabbit. How it managed to bite through that live brown cable and survive, I'll never understand.
I made sure that the workshop was thoroughly rabbit-proof after that!

Al.

[mole42uk]

I once had to deal with an entire fuseboard that had been made dead by a slug which had shorted L to N and tripped the main breaker. Fried slug isn't a nice thing :-(

Years ago I used to install and repair juke boxes. One pub's pet rabbit had stripped the insulation off many yards of speaker cable, then turned its attention to the mains supply cable. I saw said rabbit, alive and apparently well, after the live and neutral had touched and fused the supply.

[G6Tanuki]

I had a small remote VHF repeater-station go down once after one of the local Red Deer stags got his antlers catastrophically entangled in one of the guy-wires and dragged the mast over at a rather inelegant angle in his attmpts to get free.

The free venison kinda made up for the hassle of the callout.

[richrussell]

Maybe those in insect prone areas need to return to 1950s 'tropicalised' electronics, complete with wax seals and drenched in DDT

[camtechman]

Some years back I popped into my local Indian restaurant to order a take away. I was the only customer at the time, the restaurant having only just opened.

Whilst waiting for my food to be prepaired, one of the staff offered me a free soft drink and then he attended to the double jug coffee maker. He switched it on and disappeared into the kitchen, leaving me alone to consume my drink.

A few minutes later, there was a load bang & a blue flash from the base of the coffee maker at which point the waiter came running back into the restaurant and was quite puzzled as to why it was longer working.

As they staff knew me well, not only as a regular but also someone who was skilled at "electrickery", they asked if I could help. Having seen the event and where the blue flash came from, I guesed something had happened in the base of the unit and so, the staff produced a screw driver and I removed the base plate.

Guess what I saw?........a small brown mouse straddled across the mains switch and with it's teeth burried into the live wire running from it....poor thing looked as stiff as a board !

I cancelled my order for my take away and left.

[G4XWDJim]

Some time ago I was brought a French domestic radio a, 'Pont Bleu" I think it was, to repair by some friends who purchased it from the owner of a French B&B where they had spent a week each year for the last few years. Each year this radio had become quieter and more tinny sounding until on their last year there they were able to persuade the B&B owners to sell it to them.

When I opened it up there was virtually no speaker cone. Just a half inch strip where the wires fed the voice coil. It had been completely eaten away by mice who left plenty of droppings behind, together with a very rusty chassis.

Jim

[cmjones01]

I've just been repairing and adjusting a lovely old oak-cased Sifam ammeter for use in the workshop. I had to add a shunt to it, since the original had gone missing, and was checking it against a digital meter. I couldn't work out why every time I adjusted something, or even put screws back in the case, the reading became a bit low. Eliminating everything else, I checked it against a second digital meter and found it was under-reading by a factor of 2! I then checked it against an Avo 8 and another indirect means of measuring the current and found that both digital meters were reading wildly wrongly, and the first one gradually drifted, hence the variation in my measurements.

Just goes to show, I shouldn't trust rarely-used ranges on multimeters...the two meters in question are in daily use for measuring voltage and resistance, and have never missed a beat, but the current ranges are very sick!

Chris

[Refugee]

The one I had was slugs on the PCB in a pair of electric gates.

[McMurdo]

slugs on the PCB in a pair of electric gates

In the day job I often repair electric gate boards and slug ingress (and a big bang) is the most common problem. They can get in through seemingly hermetically-sealed enclosures! They rarely leave!

On the subject of unwanted creepy crawlies, I once had an electric motor sent for repair from Morocco. It was snowy weather and the motor was frozen having been in the courier's van for so long. Inside the motor was a strange frozen spider..which appeared dead and I ignored it. Imagine my horror when it thawed out and came alive in the warm workshop. Probably harmless but I didn't let it prove me wrong!!

[G6Tanuki]

We think we've got it bad: I can only offer these couple of pics from the USA utility-industry:

http://www.mtfca.com/discus/messages/50893/76324.jpg

http://www.mtfca.com/discus/messages/50893/76325.jpg

[mole42uk]

That's what you get for only 110V.
If they'd had real voltage it would have been fried snake. Suppose someone would have eaten it.

[plaka78]

I can remember doing a call out to look at a Hitachi Video Recorder in the 80s, The probem was the Head speed going out lock in 3 seconds intervals. I took the bottom cover off (Bearing in mind the gap between the bottom cover and the circuit board was approx 10mm) There was a dead mouse in the process of decaying.
Remove mouse and clean the print and all was well. The customer was amazed how the mouse got there

[russell_w_b]

This is what you tended to find when ratching in the lower parts of the Harris HF transmitters on the BBC British Eastern Relay Station, Masirah Island (as was). This and snakes...

You should've seen its mother!

[Refugee]

I have just spotted a spider trying to get into my computer and it appeared to have given up and was hanging on a dusty ledge and doodling with dust on the front panel
I got a plastic box and held it below and lightly touched it.
This made it curl up like a hedgehog or armadillo and drop into the tray so making it easy to evict it to the garden where it can get on with eating pests as it should be doing.

[Sideband]

Originally Posted by Phil G4SPZ

I discovered that both bulbs' dipped beam filaments had failed at the same time.

Not dipped beam but a few months ago whilst waiting at a roundabout, another car drew alongside me and the driver said through the open window, 'Your brakelights aren't working mate!' Startled, I politely thanked him and drove home cautiously (fortunately only a mile away and on fairly quiet roads). He was right! BOTH brake lights had failed and I'd only checked them a week previously.....