I should have known better. Its not the first time.
I have a power supply. It has one of those switches with a neon lamp inside, to let you know that it is on and has power. Like many of these things, the neon lamp failed long before the switch was ready to quit.
I like the power supply, but with so many places for things to go wrong or get disconnected, switches left in the wrong place and so on, it is really handy to know if there is AC going in and DC coming out of the box. So in a morning’s burst of enthusiasm I decided to take a bit of time out to fix the problem.
Some magazines used to call this sort of thing an evening project. More realistic ones called them “weekenders”. Getting to the switch was no problem, getting it out wasn’t much of a problem.
The optimist in me said “I’ll just open the switch up and replace the neon lamp”. Before the realist in me could object, the switch was moving in 3 different directions, with some bits moving to another dimension somewhere. So much for replacing the neon. Time to look for another switch. After an hour of looking for a similar switch I found one in a piece of junque. Getting it out required a good chunk of plastic surgery. Glad it was a plastic case. Two problems: it didn’t fit, and the neon lamp was ALREADY dead. Problem one was fixable. I have a nibbling tool (and a selection of files) and the new(er) switch was bigger than the old one, so I could make the hole in the case fit the switch. Problem two meant I needed to give up on the idea of a lighted switch and just put a LED on the front panel. (At this point I realized I could have saved hours if I started with this approach). The same piece of junque that donated the switch also donated a green LED. It didn’t donate a resistor. No problem, I figured 12V, a couple of milliamps or so, around 6k ohms should do it*. More rummaging around the heap found a resistor with a red multiplier band. 5.1K, close enough. I had some fancy LED surrounds and knew where they were, so started drilling the front panel. Part way through the drilling, I paused to look for something to stop the drill BEFORE it went into the guts of the supply. Disaster averted. Soldering the wires to the LED would have been easier if I did it BFORE I installed it into the panel, but it was still manageable. The only thing left was to close the box, except that it the switch was wired inside the case, but had to be pushed in from the OUTSIDE. Two steps forward, one step back, again.
Finally, I get a break when putting the case together for what I hope is the last time. Before giving up searching for the missing bits of the original switch, I found a screw that, it turns out, is a good replacement for the one that was missing when I took the case off for the first time. I guess something had to go right. I missed a nice day outside, but with any luck there will be more of them, some day.
73, Smile, it’ll feel better even if you don’t mean it.
mk
*Those of us from the slide rule era don’t worry about whether it should be 12V, or 13.86V, or one of those minus the voltage drop of the lamp, or whether the LED wants 2 or 20mA, since anything between “it lights up a bit” and “it blows up” will do.
Last Updated on 2026-03-05 by Eve