Keith's Electronics Blog

After repairing the Alesis monitor speakers by replacing overheated electrolytic capacitors, and then having one break again within a couple of minutes the first time I used it, I started to get a little paranoid about electrolytics and heat. In particular, I wondered, am I baking the electrolyte and ruining the capacitors when I bulk-desolder with my heat gun?

Gave it a little test today. The power supply board from the dead Optoma projector had a bunch of nice electrolytics on it, so I tested their ESR with my Capacitor Wizard, desoldered the board with the heat gun, and tested the caps again.

No perceptible increase in ESR, and I’m really glad to know that I haven’t been (directly) ruining capacitors all along. Yes, the extra heat probably speeds them on their way; but at least it’s not immediately fatal.

Friday night, I harvested the components from this board using the heat gun.

Time spent

• straightening leads with a chisel: 10 minutes
• heating and pulling components: 15 minutes
• sorting and putting away components: half an hour

And the sorting time would have been spent anyway if I’d bought the parts in a grab bag.

The take:

• several nice terminal strips, connectors, and a fuse holder
• a handful each of electrolytic and non-electrolytic capacitors
• a handful of resistors
• a handful of diodes, including two Zeners and some 1N4007 rectifiers
• miscellaneous transistors
• miscellaneous ICs, including a speakerphone IC (ah! so this was a dead board from a campus emergency call system), tone generator and detector, low-power audio amplifier, and serial EEPROM
• the inevitable transformer

Not bad, to my way of thinking, for an hour’s free entertainment.

Sorting and Storing

After salvage comes sorting and storing, which are mostly common sense. Here are some things I’ve found to minimize the tedium of sorting and to optimize storage.

My basic principle of sorting is to do so hierarchically. So I first group simmilar components, as shown above. Some components, like connectors and digital logic chips, go straight into bins without further sorting by type or value.

Resistors and capacitors I sort by decade (multiple of 10) immediately and by specific value later.

If I find a batch of several identical capacitors, I like to keep them together in a small bag. If I’m working on a project and want identical caps for aesthetic or technical reasons, it’s easier to grab a bag than to pick through loose caps in a drawer.

Then the capacitors (and bags) go into drawers labeled (approximately) by decade — electrolytics above, others below. Common values of physically larger caps may get split up into their own drawers.

It’s easy to pick out 10X-valued resistors while sorting by decade, so I do that up front (the upper row — 10Ω, 100Ω, 1KΩ, 10KΩ, and 100KΩ). The mixed resistors (lower row) go into a decade drawer

and get put into a row in the parts cabinet for now.

Then sometime later, I’ll go through the decade drawers and sort by individual value.

I’ve seen university EE stockrooms with enough parts bins to have every resistor value in a separate drawer, but most of us don’t have that much money or room for storage. I suggest going to hobby/craft stores and looking for storage solutions designed for beads or for embroidery floss. Bead storage in particular is good about sealing each compartment when the lid is closed, to keep beads resistors from migrating about when the storage is moved or shaken.

I spent several evenings driving all around Wichita a few years ago and came up with these trays, I think for floss, which are perfect for salvaged resistors. (New resistors may need the leads bent a bit to fit in the drawers.) I bought a tray for each decade and have a stack of them sitting beside my workbench.

Most of the resistors I salvage are 5%, which has 24 standard values per decade. I made a spreadsheet of all such values to fit on adhesive return address labels, Avery number 5267, and stuck a label into each spot in the tray. I’d offer the spreadsheet for download, but for some reason I can’t find it any more.

Knowing what kind of equipment to salvage for electronic components isn’t enough; you have to know how to get the parts out, or you’re just stockpiling junk. Through-hole ICs may be best stored on the original circuit boards to salvage when needed; but common components like resistors, capacitors, and diodes are much more economical to salvage in bulk, then sort, store, and have ready on demand.

I desolder with a heat gun and pull the components out with pliers. I destroy a few components on nearly every board I salvage; but it’s incredibly fast compared to any other method I’ve tried. For me, the time savings I discovered when I switched to using a heat gun was what made it really worthwhile to salvage components in bulk and stock up my parts bins.

Here’s a circuit board that one of the electricians at work brought me. I don’t know what it does; but he works a lot with the elevators and it’s probably something out of an elevator control system.

It’s not representative of the resistor- and capacitor-laden boards I particularly advocate salvaging; but I had it on hand and it does serve to demonstrate my method.

Uncrimping Component Leads

Through-hole components on commercially-produced boards tend to have their pins crimped on the solder side, to hold the components in place during the time between stuffing and soldering. Even with the solder melted, you can’t pull out a crimped component with pliers, so the first step is uncrimping the leads.

I use an cheap 1/4″-tip wood chisel from a dump bin at my local Ace Hardware store. (This is “my best $3 chisel” that I’ve referred to before — my real wood chisels never come anywhere near metal.) It doesn’t need to be sharp, but the edge should be fairly straight. I use a similarly cheap diamond honing board to clean up the nicked edge from time to time.

I push the chisel into the solder under the lead and lever up to straighten it. It’s important to get the chisel edge all the way to where the lead comes out of the hole, or you won’t be straightening the lead; you’ll be putting another zig in its zag.

Keep your other hand out of the path of the chisel. I’ve slipped the chisel off of leads, cut leads clean off, and tried to pry up solder pools that didn’t have leads in them. All of these result in a narrow, sharp object moving forward at high speed with a fair bit of pressure behind it. Again, think about where the chisel is going to go when it slips and keep your fingers out of the way.

It took only a couple of minutes to uncrimp the few leads on this board. Larger boards may take five to ten minutes; CRT motherboards can take half an hour, and I tend to do them in sections because uncrimping leads is really tedious and boring.

Heating and Removing Components

Once the leads are uncrimped, I clamp an edge of the board into my bench vise and get ready to heat it up. You need a bench vise that’s heavy or bolted down — you’re going to be prying and wiggling on the components quite a bit to get them out.

Now is a good time to remove fuses from holders, and optionally remove any socketed components from their sockets as well.

I use a cheap heat gun that I got for $15 at Harbor Freight. I regard it as a disposable item — I go through one in about a year (during which time I’ve salvaged far more than $15 of components) and go buy another.

Starting at the bottom edge of the board, I heat the solder side with the gun 1-2″ away until the solder melts, then pull out the components with a needlenose pliers and drop them in a cup. It’s faster and easier for me to put them in a container and sort them later than to place them carefully on my workbench and have them get brushed around, but your mileage may vary.

Some notes about the actual desoldering and component removal process:

• The first component is going to take a long time to heat up. Be patient; pulling before the solder is fully melted will just break the part.
• You can see the solder melt. Watch for it.
• Start at the bottom and work up a column, angling the heat gun in the direction you want to go. It’ll start melting the next component’s solder while you’re removing the previous one. You can go quite fast on a stack of properly uncrimped resistors.
• Get out the regular pliers for larger items, and particularly for DIP components. Rock them back and forth very gently until you can see that all the pins are loose, then slip them free.
• Don’t hang onto a resistor lead with the pliers while you’re heating it — you’re just making a heatsink and preventing the solder from melting. Heat the solder, then grab quickly with the pliers and pull. You may get both leads in one pull; or you may get one end loose, readjust your grip, and get the other end.
• TO-220 parts may fit tightly enough that they don’t want to come loose even after the solder melts. This can mean pulling the plating out of the through-holes, which then means cleaning the tubes off the leads later. A giant 3/8″ chisel-tip soldering iron laid across all three leads will pop a TO-220 free in an instant.
• PC boards are flexible, especially when hot. Long strip connectors may require freeing one end and bending both connector and board as you work along the connector to free the remaining pins.
• Larger heatsinks (PC power supplies and CRT motherboards) may have tabs that need to be untwisted, and their tabs or posts may fit tightly through barely large enough holes in the circuit board. If necessary, save them for last and force them out with large pliers.

This sounds obvious, but when you’re done desoldering, the circuit board is still hot. I hold it with pliers while loosening the vise, then lay it on the concrete floor to suck the heat out.

Make no mistake, this is a destructive process. The circuit board will be ruined, and the fumes from scorched fiberglass are probably not good for your health nor for your relationship with your significant other or housemates. It’s best to do this as close to the outdoors as you can get and with windows open and forced air ventilation, if you have the option.

Finally, recycle the board if you can. We have a very thorough curbside recycling program here, and I’ve set out a large box of stripped circuit boards (with an appropriate note) for copper reclamation.

Sorting the Spoils

Here’s the cup into which I dropped the parts as I was pulling them:

And the parts sorted on my workbench:

I got a couple of terminal strips, several DIP sockets (one irreparably damaged), four TTL ICs and two resistor packs, eight NPN transistors, diodes, LEDs, one capacitor, and fuses and fuse holders. Not great, but not bad for fifteen minutes’ work.