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PostPosted: Sun Dec 17, 2017 6:07 am 
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Hi all

I recently was fixing a broken electrical component for a relative's lazy boy recliner and it got me thinking, what would I do to repair stuff of an electrical nature when I couldn't duck down to the shop. I can build basic circuitry but this got me thinking.

What do people stock up on, resistors, capacitors, duct tape?

interested to hear, currently building up my stock of bits for future projects

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PostPosted: Sun Dec 17, 2017 11:09 am 
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taipan821 wrote:
Hi all

I recently was fixing a broken electrical component for a relative's lazy boy recliner and it got me thinking, what would I do to repair stuff of an electrical nature when I couldn't duck down to the shop. I can build basic circuitry but this got me thinking.

What do people stock up on, resistors, capacitors, duct tape?

interested to hear, currently building up my stock of bits for future projects

If you have access to a dump/landfill then you have access to the majority of the parts you'll ever need. The issue then becomes one of having the correct gear to harvest those parts and make use of them. Gone are the days of hand wired TV and radio chassis that you could easily scavenge parts from. (I joke that I put myself through high school just walking my neighborhood on trash day and either bringing things home to repair and resell for pocket money or just harvesting parts from discarded electronics.) Nowadays everything is SMD and, often, multi-layer PCBs. While we can harvest SMDs with a good rework station it's difficult and time consuming. It also requires good reference materials to be certain of what you have. With multi-level boards though, any failure of a component on the board is going to kill the board, unless it's a surface mounted component that you can replace or bypass without killing anything in the sandwich of layers beneath it. So, for many things, spare boards are going to be the best way to go and therein lies the rub, you can't stock replacement boards for everything you have or might come across in a ZPAW. For that reason, I generally keep two (or more) of the things I'm really going to need in a ZPAW. This includes about half a dozen old smartphones filled with handy apps, ebooks and PDF files of important information that would be needed. Several of those apps have to do with electronics and ham radio and a couple are an absolute requirement for anyone wanting to do repairs ina ZPA(no internet)W. Electrodroid Pro is one such that I highly recommend. I have it on every smartphone and tablet I own, and I keep it updated. I also recommend grabbing a few of the many apps that provide databases of pinouts and component lists. I don't worry too much about some of the free apps having ads. Without a data connection of some type the ads do nothing, but the databases the apps provide are part of the app itself, so no connection needed.

For tools, I keep my trailer stocked with a couple of gate mouth tool bags stuffed with various hand tools and things like tape (electrical/friction/silicone), zip ties, etc. I also have several of those Harbor Freight medium and large plastic portable parts storage bins. They are filled with things like heat shrink, connectors (and the proper hand crimper jaws needed for them), jumpers and test leads, common parts (like LEDs, resistors, some caps, etc.), and various fasteners. There's also two large Pelican cases I have that contain a complete rework station, solder and solder tools, DMMs, a small battery operated scope, two different sizes of heat guns, frequency counter, frequency generator and a 30amp variable DC power supply. While the scope isn't a great one (built it from a kit) it does work and can be used for simple things. Of course, a lot of this requires AC power to use, so the trailer is equipped with roof-mounted solar panels, a small (200ah total) AGM battery bank, a 2kw pure sine inverter, and a 7kw gasoline generator. (Trailer also has LED lights, workbench, propane heat, a portable A/C unit, portable toilet, 70cm ham repeater, portable broadcast TV receiver, dual band ham radio with APRS, and an IC-706 MKIIG ham radio - working on getting some more roof insulation installed and a folding bunk in it.)

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PostPosted: Sun Dec 17, 2017 12:55 pm 
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While some repairs of modern equipment would be immensely impractical, even with access to a fully-stocked workbench, a good fraction of the things that let the smoke out in electronics are actually things you can fix. It might not be pretty, or resemble the original design, but you might still be able to hack it with a handful of tools and a good stock of supplies. Obviously, a multimeter and soldering iron are bare necessities, but with those two you can find and fix a lot of these problems.

In my experience, capacitors are by far the most common thing to die. Usually by overvoltage or just heat stress, and they typically are one of the lowest quality components on a board. A good stock of electrolytic, tantalum, etc. caps can get you running again when one of those explodes. The ceramic caps are usually less likely to die than their larger electrolytic counterparts.

Second to capacitors are actual physical switches and buttons, which usually serve as interface devices for us humans. People are not often kind to these things, and they get a lot of physical stress during normal use. Thankfully, these are also usually the easiest to "fix" - using this term loosely, since you usually have the most flexibility about what kind of fix is acceptable in this arena. I've replaced small switches with much larger ones (with wires strung back to the original switch contacts), in cases when that is all that I had on-hand. Other times, two bare wires you touch together by hand (low voltage only, of course) would be considered acceptable to at least get you running again, and I've also just hard-wired selector switches into an acceptable position for a temporary fix.

Thirdly, transistors, MOSFETs, relays, and their ilk. These usually die from exceeding their power capacity or just inadequate cooling again. A handful of common power transistors, and maybe some solid-state relays could be useful in a pinch. Usually the power transistors are more likely to die than their low-power signal cousins, based on the kinds of electrical stress they see, but maybe a few signal transistors as well.

And finally, diodes are the only other thing that I'd expect to be able to diagnose and repair on short notice. They are usually pretty durable, but on rare occasion they get blown out, and are usually pretty simple to swap.

A lot of the expedient repairs I've done resemble the "dead bug" style, which would cause nightmares to any PCB designer (and myself sometimes), but if it works for getting you out of a sticky situation, then it's fine by me. If you have the time and resources, at least try to fix it properly later. :)

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