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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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PostPosted: Thu Jan 04, 2018 12:10 am 
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JayceSlayn wrote:
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. :)


I got a chuckle out of this. I'm an embedded systems designer, and I've been designing circuits and PCBs since the 90's. On some complicated designs (and even some simple ones!), it's unlikely that the initial prototypes will be 100% correct. That often leads to some ugly and interesting rework.

Back to the OP, first, you need a place to work with decent lighting and maybe a static mat. For repairs, you need to be able to determine what's wrong. This typically requires tools like meters, scopes, and logic analyzers. If you travel or are just starting out, something like this http://store.digilentinc.com/analog-discovery-2-pro-bundle/ is good. I'd also get a small multimeter.

It's also very helpful to have schematics and PCB layout details for the thing you're repairing.

Other tools: I need a microscope these days. With good magnification, you can often find the source of a problem (poor soldering, cracked solder joints, bad etching on PCB traces, etc.)

Another very useful tool is a thermal camera. These can be used to find a bad component in some cases.

Also helpful is a lab power supply where you can adjust the output voltage and the current limit.

A good selection of spare wires: bare wire of all sizes on spools, various USB cables, test leads with alligator clips and hooks, power cords, etc.

A software defined radio can be used to "sniff" for signals on a PCB with a small, handheld loop antenna.

A signal generator is useful for injecting signals at various stages.

Resistor and capacitor decade boxes can be helpful too.

A good soldering iron, solder, solder wick, flux, picks, tweezers, wire, epoxy, prototyping board, and a good selection of spare parts help, too. The spare parts will depend on your skill level.

Finally, I think that development boards like Arduinos can be helpful. If you lose some logic chips, you can easily program logic functions into something like that.

These things take years to accumulate, so start with the basics and build from that. Ebay is your friend here!


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PostPosted: Thu Jan 04, 2018 12:32 am 
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I used to repair all my electronics when they were expensive to replace. But I stopped in 2009, when one of the lights went out behind my (at the time) very expensive monitor. I took it apart diagnosed it, found the part, and realized that the part, controller for that florescent tube cost more than a new monitor. That was the say I said eff it and stopped. I still like to build circuits but only for a hobby. I'm currently building a very large battery pack that can hopefully be used at the property once I get it finished as a supplemental power source during peak hours until I get some solar/wind up and running.

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PostPosted: Thu Jan 04, 2018 6:05 am 
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Halfapint wrote:
I used to repair all my electronics when they were expensive to replace. But I stopped in 2009, when one of the lights went out behind my (at the time) very expensive monitor. I took it apart diagnosed it, found the part, and realized that the part, controller for that florescent tube cost more than a new monitor. That was the say I said eff it and stopped. I still like to build circuits but only for a hobby. I'm currently building a very large battery pack that can hopefully be used at the property once I get it finished as a supplemental power source during peak hours until I get some solar/wind up and running.

Second on this, unfortunately. That is part of the impracticality of fixing some things lately. We have the almighty power of "economy of scale" to thank for how it is possible to create a PCB out of parts sources all over the planet, manufactured in one country, integrated with an aggregation of other components in another country, and finally shipped to your doorstep for $29.99. It amazes me still, that there are so few things that I could fix on a typical appliance by myself, that would cost me less than the same appliance new. I think that the scale efficiency of modern manufacturing is greatly responsible for a "disposable/consumerist culture", based largely on that fact that for each individual, it is just cheaper to buy a new thing than to fix it. The fact that each year's latest smartphones cost only $800 should be astounding as well.

Generally, I'm only into the "expedient" fixes now, where the thing that is broken needs to be brought back into service before a replacement can arrive. E.g.: the thermostat in my house broke the other day, and stopped sending the control signal to the furnace to turn on the heat. In an already cool (of course I wouldn't notice until something seemed amiss) and rapidly-cooling house, I wanted to troubleshoot the problem before I go out to get a new thermostat anyway. But once I found the problem, I just decided to "fix" it, as it would be cheaper and quicker than even going down to the home improvement store for another one. Problem was that the contacts had somehow "disappeared" from behind the "Auto/Off/On" fan selector switch. How a switch disintegrates like that I don't know, but the fix was to solder two pieces of wire across each set of contacts to permanently enable the "Auto" setting - as that is all I can think I've ever used anyway. This is a fix that I'm pretty happy leaving put for now, but eventually the replacement will only be about $20-30 for the whole thermostat, or about $1 + shipping for a new switch (though I've yet to find one with the exact correct post type on DigiKey, to fit the cosmetic switch cover).

Still, the skills of being able to troubleshoot and fix minor things by yourself will save you a lot of time and money from paying someone else to come and replace your whole thermostat for you. I think the vanishing art of simple repairs is something that should be kept dear. Not just limited to electronics, of course.

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PostPosted: Thu Jan 04, 2018 9:46 pm 
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Great topic.

Assuming you can not quickly and inexpensively replace the failed electronic device, its nice being able to repair the most common failure modes.

Having had repaired high end consumer audio and video equipment for 7 years in the way back when:

number one failure mode for majority of the older stuff was 'cold' solder joints. Another tech in this thread referred to these as cracked solder joints
These failed or intermittent joints were usually observed at the solder pads for high heat generating components. These components would cause expansion and contraction at the component lead solder pad interface, resulting in intermittent circuit continuity. Components prone to do this would be current limiting resistors, B+/- power regulators and or power transistors and shunt devices such as Zener diodes. Usually located in the power supply section of a PC Board. ALWAYS remember to depower equipment when removing/solder components. Also if there are large capacitors, drain them using a beefy 5 or 10 watt 10 ohm resistor.. Clean up the old solder with wick and resolder with rosin core electronics solder. If possible add a larger heatsink to the power regulator so it operates at cooler temp in future. If you have a replacement component that's caused a cold solder join, it's usually wise the replace the component while you at it.

So a good basic repair kit should have tools to open and access the electronics within. A good multimeter, high quality solder and iron, solder wick, and a patient eye.

Second common failure mode, blown fast acting glass fuses. Most of todays electronics have them, usually on posts inside the unit, close to line voltage input or the power regulator section. So add a common selection of fast acting glass fuses. 1/2 through 5 amp should cover ya.

Third common failure mode oxidized/intermittent switches, relay contacts, molex and/or similar connectors. Pencil erasers, emery cloth, spray contact cleaner are a must for a basic electronics repair. Disconnecting and reconnecting oxidized connectors often help restore continuity.

As also mentioned schematics for the piece you are trying to fix really helps. It's dependent on skill level and the ability to diagnose to component level.

That's my 3 cents.

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