What's the weirdest fault you ever fixed?

[Enzo]

My junior tech asked for some help once on a Yamaha casette deck. This casette could record on all four tracks, and came in a package with a small patch bay and a little mixer. I am thinking maybe MT-44? Would only record on two tracks. Tracks 1 and 2. Tracks 3 and 4 recorded on the side of the tape normally reserved for the other direction, but wouldn't work for us. You could still use it for regular stereo casettes too.

I decided we would troubleshoot together. 3 and 4 not recording. Nothing coming out the record amps. Traced that to some sort of controlling part not turning on. Traced that to some control signal absent. FOund the thing that worked that, and found my self step-by-stepping back through the system until I found a photosensor on the transport not turning on. The sensor looked out through the front. SHined a light on it, it worked.

It turns out, that this deck worked as a normal stereo deck unless you put a special adhesive sticker on the blank cassette. The sticker was reflective, and it reflected an LED light back into the photosensor. This turned on the tracks 3 and 4. Without the sticker on your casette, you got only two channels.

We had troubleshot the problem all the way through the unit and out the front.

My tech was wailing that we had wasted a lot of time. I told him, "No, we just demonstrated to ourselves that we know how to troubleshoot." We took the long way, but we got there.

And that explained this mysterious sheet of shiny sticker labels in our Yamaha drawer.

[poynton]

Originally posted by G.Kleinschmidt
.....................I bought a stud finder..........................
It just beeps continuously whenever I get within two feet of it.

Are you boasting ?
Some sort of sexual innuendo ?



Andy

[Geek]

Originally posted by poynton

Are you boasting ?
Some sort of sexual innuendo ?

It's a joke as olllld as the dang gadget itself

[GK]

Soooory.

[Netlist]

Years ago, a dead Crown – I believe a Macro-Tech – came in that I was unable to fix.
When it returned from Crown service department, a 1k resistor was replaced and they had included the old, supposedly broken one. I measured the bad resistor but it still measured a perfect 1k.
Later I fixed several other Crowns with the same problem and it was sure not a bad solder joint. Till today I don’t get why replacing a perfectly good resistor did cure that problem.

[SY]

Hugo, a few possibilities:

Tempco
VCR
Resistor going open with heat

I can't think of any weird troubleshooting issues I've had, but I can sure think of quite a few stupid mistakes I've made, followed by hours of wasted work, culminating in a Homer Simpson, "D'oh!" My favorite was the buffer with a gain of two...

[Netlist]

Yes, possibly. Unfortunately, I never tested the old ones other than ohmic out of circuit.

[GK]

Had just finished soldering and wiring up the circuits I designed and layed out for a nuclear bole hole logging tool used for stratigraphy surveys. These consisted of a couple of photomultiplier and neutron tubes along with regulated SMPS HV supplies, pulse amplifiers, threshold detectors and a bank of PIC uC’s for counting/averaging the multiple scintillation channels and serially telemetering the data via the logging line to the surface equipment. I proceeded to power up and test the tool on the workbench with a mild caesium pill to safely raise the background radiation. Everything worked fine except for the baffling occurrence of a huge pulse that would saturate the PMT preamplifiers at seemingly random intervals. Maybe 2 minutes apart or as many as ten. Spent the most part of a day trying to track down the fault, until someone informed me that "those are just cosmic rays".

Another day I fired up a similar tool to start calibrating the threshold detector for the neutron counter, but could not figure out why the counts were so high (should be next to zero with normal background radiation). I suspected oscillation in either the preamplifier or the neutron tubes HV supply, but couldn’t detect any.
After a few wasted hours I suddenly remembered that I had gotten our “neutron bomb” (a paraffin wax filled steel sphere about 1.5 times the diameter of a basket ball, housing/shielding a sealed neutron source in the center) out of the radiation pit the night before, and put it under my bench. I had been resting my feet on it that entire morning.

[Pano]

Originally posted by Enzo
It turns out, that this deck worked as a normal stereo deck unless you put a special adhesive sticker on the blank cassette.

Clever!

Originally posted by G.Kleinschmidt
a couple of photomultiplier and neutron tubes along with regulated SMPS HV supplies, pulse amplifiers, threshold detectors and a bank of PIC uC’s for counting/averaging the multiple scintillation channels and serially telemetering the data via the logging line to the surface equipment.

Say that 3 times fast! (sober doesn't count)

[GK]

Originally posted by panomaniac

Say that 3 times fast! (sober doesn't count)

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.