Microcontroller hobbyist and electronic project enthusiast can stock up on useful parts by scrounging. Before you throw away an electronic device, take it apart. Examine how it was made and what parts were used. Look for reusable power supplies, microcontrollers, connectors, LCD, LEDs, knobs, meters and even the enclosure.
This article describes a recent scrounging project on a 3Com Super Stack II switch. This Ethernet switch was purchased to use in a home network for $10 at a Goodwill computer store. Unfortunately it was discovered later that the device had very loud fans and was actually only a 10MBit switch. Instead of just throwing it away, it was gutted for parts.
WARNING:
Wear eye protection and gloves. Hot air de-soldering is very dangerous. The process should be done by two people, especially on large PCBs like this one. Read the How-To and FAQ for more detailed instructions.
Victim:(click for larger pictures) |
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Guts:A large PCB with interesting parts. Power supply, LEDs, Oscillators, surface mount tantalum capacitors, transistors and some interesting ICs.The fans are noisy but they do blow a great deal of air. Might find some use for them. |
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Close up of the LEDs. Notice the metal oscillator can in the upper left and the yellow tantalum capacitors (yellow bricks). The LEDs can be removed from the black plastic PCB mounts if you need singles. |
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The power supply is the best reusable part. Astec Dual output, 5VDC@15A and 12VDC@1A. It has a nice AC power connector like a PC and the output wiring is labeled making it very easy to reuse.If we don’t use 15A on the 5V the fans will probably not be necessary. |
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Surgery:Here you see the PCB on a metal plate to protect the work bench. A suitable heat gun |
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Heating the PCB to remove the LEDs. The gun easily melts the solder so that the LED modules just fall out. You can pull on them if necessary but watch out, the hot air will burn instantly.You can light a cigarette in the air flow and paper will burst into flames. Be very careful! |
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Heat from the top to remove surface mount parts. Use a pair of tweezers to lift or scrape the parts off the board.Some parts will melt under the heat and others may fail due to excessive heat. Use just enough to do the job. |
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I removed one of the vary large parts to see how it was attached. The large IC on Left is the same as the disordered one, upside down on the right. The pad set is shown center. |
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Many of the salvaged parts shown here just fell off the board. I don’t plan to save all the ICs and resistors shown. |
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can be purchased at AmazonResults:
| Quantity | Description |
|---|---|
| 1 | Astec Dual output, 5VDC@15A and 12VDC@1A |
| 1 | Power Supply connector |
| 3 | Oscillators: 33.33MHz, 40.00MHz, 50MHz |
| 40 | LEDs: 22 Green, 18 Yellow |
| 5 | 64K by 16Bit SRAM, CY7C1021 |
| 1 | PCB Mount DB9 Male. |
| 28 | Tantalum caps: 1 47uF, 11 10uF, 16 1uF |
| 9 | Surface mount transistors |
9 Responses
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yep that seems to work just fine… actually for while i did some smd soldering-on jobs with a (much smaller) hot air de-soldering device… worked fine!!
greetz
Yes, it works. Most of the parts I have right now came from scrounging like this. I need to get some resistor and capacitor assortments but I plan to keep on scrounging.
I have done a bit of etrash scrapping myself. Though I have never tried a hot air gun, I use a 5 pound solder pot myself. I have nicknamed that device “The Volcano”. If truth be told I have actually done a lot of parts harvesting. Another very popular method I have talked to people about is using one of those Bernzomatic propane torches to bulk desolder PCBs. That, and get an empty cardboard box and use what we in the industry refer to as the, “heat it and beat it” technique. Where you heat a section of the board then quickly flip it over and beat it on the edge of the cardboard box, letting the parts fall into the box. There are variants to this technique, the good old slap it on the desktop method is popular too. It takes less forethought, and maybe a bit more running around to retrieve all the parts, but it is another widely used technique none the less.
Though this technique only works with boards where component leads have not been formed, and there is enough loose play clearance. When it does work well, the parts come out like rain. I should add one tip though, with any of the beating, or slapping techniques beads of molten solder are released from the board too, if you don’t pick up your parts, or sweep them to the side or something, you will end up with some parts getting beaded in the next cycle of the process.
Also, some strategy comes into play with bulk desoldering. Heat is destructive to all components in great enough quantities, or duration. So, plan your attack to liberate the most heat sensitive, or desirable parts off a board first. Typically I will go after semis first, then capacitors, then resistors. As their name would imply, resistors can really resist some heat usually.
Many scrounged parts are of a higher quality than an experimenter can typically buy. Professionals assembling PCBs often have better sources for parts than amatuers. Some of the obsolete tech from the 80s that cost tens of thousands of dollars when it was new was put together with some pretty nice stuff! I have scrapped a couple of ancient mini computers, unreal the components in those. Junk boxing as it is called is a time honored tradition in the electronics hobby community. You’ll always have to buy some parts, but the more you can dredge up out of your junk box the greater the pride of accomplishment, for me at anyrate. Any idiot can spend money I always say.
I’m glad to see that you folks aren’t wasting your time trying to use soldering irons to bulk desolder PCBs. I did, I suppose we all have, it doesn’t really work. Desoldering rework stations are for when the PCB is still the most valuable component in an assembly, when it comes time to scrap something for parts, I say throw another PCB on the barbie!
Thanks for the comment Paul, lots of good information and advice.
One idea I wanted to try was using a skillet and some sand. I have seen this done before for single sided through hole PCB scrounging. Basically you just put some clean sand in an electric skillet and heat it up. Put the PCB in the sand and use a broom handle to push the PCB down into the heated sand. Use long nose pliers to pull out the parts.
This should also work for surface mount parts but the parts on the sand side of the board might get lost in the sand.
Another interesting idea would be to somehow attach the whole pcb board to some kind a dual clamp that vibrats enough that if you heated the pcb from the bottomside with the heat gun, that everything would eventually fall right off. Would be a great way to entirely strip a pcb board.
Yes.. Might be simple to make a fixture that the board could hang from on one corner. The fixture would rotate so the board sweeps around in front of the hot air gun. It could also bump into a peg or something on one of it’s corners as it goes around on the fixture. Just put a box under the rig to catch the parts.
On problem I have experienced with the shake or bump method to remove the parts is that you end up with big splashes of solder across the pins on the salvaged parts. It is easy to clean up but you will end up wanting to clean them all before you sort them into your collection.
I tend to keep the boards I want to scrounge from intact and just go after the parts I need. The come off cleaner and I don’t spend much time cleaning and sorting. Of course, I don’t always know what parts I have this way.
hi i need help please send me the colour of each cable of power supply of this 3com switch, thanks..
Giovanni,
I assume you have one of these supplies which is why you want to know the voltages. Each of the supply voltages is marked on the PCB where the wires connect. It would be better for you to get the information that way as they could have changed the wire colors.
David
I always take apart anything electronic that breaks or is no longer needed at my house. I have built up a great collection of parts that have cost me nothing but a little time to get. I like how parts scrounging has become more popular with the advent of BEAM and Makers. Thanks for the great article.