I purchased a video disk player after they had been replaced by VCRs because I found one for $20 with a bunch of disks. These were analog recordings on a disk about one inch more in diameter than a 33 RPM record -- assuming you're old enough to remember the “vinyl” records. The player worked well for a year, then about 20% of the way through the record it would start to lose sync. This progressed for a while, and then, about halfway through the disk, it would stop playing.
I asked a repairman, and he told me it would be $200 to fix, as the foam rubber that the laser was potted in had become brittle. Really? A laser optics system potted in foam rubber? Years of ham radio and four years of Navy electronics told me this guy was lying. I took it apart and found a helium/neon laser in a machined cradle, and the precision movable mirrors that I expected, but no obvious problems. I visually checked the fuse and they looked good, so I tore the player apart, saving the laser and parts.
With a pile of salvaged parts, the last thing I took apart was the fuse holder to use on another project. When I had checked the fuse before, I had not removed it from the twist pull cap. I did so now, to put the fuse in the fuse drawer and the fuse holder in the fuse holder drawer. When I tried to pull the fuse from the fuse holder cap it came apart, showing a corroded end of the fuse element. The fuse element had been kissing the end cap, and as time went on, it heated up and started turning into a resistor.
If I had tested the fuse with a meter I would have probably seen some resistance. I tried putting the fuse back together in the holder and connected it to a load, and saw a small voltage drop across the fuse that slowly indicated more and more voltage as time went on. I was happy I had not paid the $300 for the player.
Years later in the Navy reserves I was asked to troubleshoot a rack of crypto equipment. This was the reserve fleet, so the crypto equipment was electromechanical. The whole six-foot rack sat there chattering at 60 Hz, and since this ship used two hot wires, no neutral, I suspected a blown fuse on one of the two fuses. The crypto tech discounted this, saying he had checked the fuses visually. I asked him to show me, and he removed one fuse (no change in noise from the rack) and then the other fuse (the rack went silent). I went back in the ET shop and got a fuse, installed it, and when the rack came back up I was pronounced a genius. I inspected the fuse, and it had blown up in the end cap just as in my video disk player.
— Paul H. Dolton has served as a communications technician for SCE for 30 years and served as an electronics tech for the US Coast Guard for 21 years before retiring. He has installed and maintained analog and digital microwave and multiplex equipment, as well as mobile radio, telephone, and EPBX systems.
Tell us your experience in solving a knotty engineering problem. Send stories to Lauren Muskett for Sherlock Ohms.