What's the weirdest fault you ever fixed?

[gaetan8888]

Hello

Ten months ago, I was working on my last amp, simulations was good, so I decide to made a prototype.

After powering on the prototype the bias was to high, the sine on the scope was top-off ... the sound was horrible, I did check every connections, every transistors, and even emailing to Hugh for help, I was not sleeping and I was still working on that little monster amp...

So in last resources I decide to test all the parts on the pcb, one by ones, wen I tested the 10 ohm base resistors of the output transistors, I discovered that those resistors did have an erronous color code, checking again with a strong ligh and a magnifier, the resistors have 10 ohm color code but it have 1200 ohm for the real value on my digital multimeter, so I pickup another digital meter, same 1200 ohm reading !!!

All my 10 ohm resistors batch did have a wrong color code, but I did buy them at a reliable electronic store !!

Sighh... I did take near two days and quite no sleep to discover that problem.

Bye

Gaetan

[Eva]

When I was 11 one of the customers of my father gave me a ZX Spectrum +2A computer that he was not using. It came with 6 games, from which one didn't work. As I got more games I discovered that roughly 40% of them didn't work either. They would crash after loading or after a few seconds working, but it was not a tape load problem.

I discovered that the problem was temperature dependent, as some games only worked briefly when loaded just after powering up the computer, and I ended up using a pack of ice on top of the Z80 (the microprocessor) to be able to play for a few minutes. Cooling the other chips didn't work.

As I learned Z80 assembler in the following years, I traced the problem to a fault in interrupt mode 2 (IM 2) in that particular Z80 unit. Memory corruption resulted (something wrong with refresh probably) when the "I" register was loaded with something equal or greater than 80h, IM 2 is activated and the Z80 is made to execute code in shared RAM (pages 4,5,6,7). Interestingly, loading a value below 80h in "I" didn't cause problems.

I learned to hack and fix some of the games that way to be able to use them when I was 13 to 15 (then I got a PC).20 years later I still keep that computer.

Conclussion: I ended up learning assembler programming and computer electronics at a very early age just to find out why the games that I liked would work on the computers of all my friends but not on mine!!!

BTW: By that time, my parents hated computers and thought they were a nasty thing. My interest in computers resulted in many problems with them. Now both can't live without a computer and internet!!!

[Pano]

Originally posted by G.Kleinschmidt
..a photon-emitting thallium-activated sodium iodide crystal.

Didn't I see Scotty fix one of those on Star Trek? Not his weirdest fix, tho. Crikey, that guy had some stories.

[GK]

Originally posted by panomaniac


Didn't I see Scotty fix one of those on Star Trek? Not his weirdest fix, tho. Crikey, that guy had some stories.

Probably not. Once the crystal goes cloudy after being subjected to too much mechanical shock, they're useless and irrepairable, like this one:

EDIT - I should give Scotty a ring, he might be able to do something with it.

[Enzo]

This one probably doesn't even qualify as weird any longer.

I had a tech working on a guitar amp for some other problem, but when he was done the amp made a steady ticking sound. He spent a lot of time looking at the power supply, and fussing around trying to find what was breaking down.


SOmeone then said, "Hey Scott, turn off your cell phone."

The phone had been sitting next to the unit.

Problem solved.

[brig001]

Not audio related, but weird. Got a call from a customer in India with intermittent problem with a motor stopping on a machine. Talked them through checking the DC drive, decided it was probably the relay that switched the speed input to the drive. Customer said it wasn't and asked me to come and fix it. Long flight from UK to India, got to machine, tapped relay with finger and the drive stopped. Removed the relay, gave it to the customer and told them the relay was broken. Replaced it and it ran fine.

Why don't people listen...

[Netlist]

Originally posted by brig001
Why don't people listen...

You have no idea how many times I tell people to check their batteries when they call me that the remote stopped working. Either they are persistent that they replaced them with new ones lying five years on their shelves or they are absolutely certain that the polarity is correct.
I change the batteries or flip them on arrival but in 90% of the cases, I'm making easy money.

[jackinnj]

Originally posted by G.Kleinschmidt



I forgot to mention that the photomultiplier tubes detect gamma radiation by means of each being coupled to a photon-emitting thallium-activated sodium iodide crystal. I’ve heard that these have medicinal properties and have been licking one for a while now.

When I took Quantitative Organic Chemistry the tech said to one of the guys "Don't put that in your pocket if you want to have kids."

[Circlotron]

The pesky boards that started this thread, well another one of them had this problem where it is supposed to turn on a relay for 20 seonds and then turn it off again but it would turn on for only about 5 seconds. The 4MHz crystal on the micro has a 10M resistor across it (brown black black green) but was in actual fact 5k1 (green brown black brown) and it made the crystal run at about 4 time it's rated frequency. I would have thought that was impossible.

The real tragedy is that the board has a bunch of these 5k1 pullup resistors and I made them 5k1 instead of 4k7 because they are right next to an equal amount of 470k resistors and I didn't want the board assemblers to get them mixed up, but they found a different way.

Murphy's Law strikes again.

[woody]

I had a dead computer that wouldn't turn on because the
hard drive had a bad power supply bypass cap. The computer
power supply was detecting this short on the power bus and
refused to power on. I connected the hard drive to an older
power supply that didn't detect the bad cap it did hovever blow
the bad cap up in a small puff of smoke! Put the hard drive back
in the computer and it worked fine without that bypass cap!