I have previously written on the joys and tribulations associated with creating one's own PCBs. Based on the enthusiastic number of comments, our esteemed editor -- Max Maxfield -- thought it might be of interest for me to write something at the opposite end of the spectrum -- stripping old printed circuit boards (PCBs) for parts.
I first became interested in electronics when I was around 12 or 13 years old. My dad was sales manager for the local branch of Burroughs Machines (of accounting machine and -- later -- computer fame) in Harare, Zimbabwe, which was then known as Salisbury, Rhodesia.
My dad was not technically-minded at all. In, fact he was not much of a DIYer in any respect, but he did encourage my growing obsession with electronics as best he could. He bought me Practical Electronics magazine every month, and also sweet-talked the technicians at Burroughs into giving me their old PCBs, along with anything else electronic or electrical off old accounting machines from which I might obtain something useful. And so it was that I acquired a growing pile of old Burroughs boards, which were populated mainly with resistors and transistors (there were no integrated circuits in those days). The resistors were carbon five percent 1/2 watt types, while the transistors were of a cryptically-marked type with a very strange case. My dad had also bought me a soldering gun (yes, a gun, not an iron) much like the one shown below, except that mine was not a Weller, but it was very similar in appearance.
Now, when they had been assembled, the boards my dad brought to me had all the wires bent over onto the copper side of the board. This meant that in order to get the components off the board, I had to heat up the joint, bend the wire back to the vertical position, and then extract it from the board. I then had to do the same with the other end of the resistor, or the other wires in the case of the transistors. This resulted in misshapen, short-leaded components, but it meant one more thing I did not have to spend my precious pocket money on.
The other problem with these boards was that, being logic circuits, there were only a limited number of resistor values used. Similarly, only a limited number of transistor types were to be found. These were, as I said above, in a very strange case, which had a dimple on the top with a dot of paint -- brown, red, orange, yellow, or green. I also had a multimeter -- a basic analog unit -- and I was able to identify the transistors as NPN types.
About a year after I got the first boards, I chanced to read in Practical Electronics about a transistor whose Hfe value range was identified by a dot of paint on the top. I looked them up further and bingo -- they were definitely the 2N2926. I've personally never seen any other transistors using exactly the same case, but there are a few as per this datasheet.
My limited range of components and lack of financial resources translated into an expertise in substitution and redesigning, which stays with me to this day. Later, I obtained a copy of Towers' International Transistor Selector, which was -- in the pre-Internet days -- a veritable bible for identifying transistors stripped from boards. I see Amazon still has secondhand copies -- not bad for a 1996 electronic components book!
A few of my friends were also into electronics, so swapping boards and components was the order of the day, but I was the one who turned into the "go-to guy" whenever anyone needed anything. I just ended up with more than anyone else. My hobby later turned into a sideline repairing radios and other electronic gear for people, and what I could not fix I bought cheap for spares.
The nice thing about stripping parts from commercial PCBs is that you tend to get high quality components from them. Boards have changed, of course, and so have my methods for stripping them. These days, my financial constraints are not as great as they were, so I don't go out of my way to salvage and use components with bent-over leads unless they are very valuable or special. Fortunately, the manufacturer's practice of bending the leads is not as widespread as it used to be.
A hot air gun is now my tool of choice. I clamp boards vertically in a vice, heat them on the copper side, and pull parts off using a pair of long nosed pliers from the component side.
In the image above we see me pulling components off an old PABX PCB. On the right-hand side is the nozzle of my hot-air gun. The component I am pulling off is a relay. This board had very limited pickings. The resistor packs you see at the edge of the board were VERY strange (mixed values in the one package). The resistors and capacitors mostly had bent-over leads, so I didn't get those off. The ICs were codecs and subscriber line interface ICs that I'm not likely to use, so I didn't remove them either.
The "spoils of war" are as shown below. Clockwise from top left we see 9V DPDT relays (useful); the resistor packs with strange mixed values (not much good); audio transformers; 100Ω 1W resistors (useful); medium power PNP (2SB1330) and NPN (2SD2006) transistors (useful); 18nF capacitors (could be useful); and DIL 1A bridge rectifiers (useful).
For some components, like multi-pin headers, I'll sometimes use a small gas blowtorch. This will quickly melt only the solder, whereas the heat gun will often melt the plastic off the component as well before you can get it off. But you have to be careful; PCBs can emit some pretty vile gases when hot, so I usually do this on windy days when I can get good through ventilation in the garage where I play (the wind blows the vile smells away from my house and long-suffering wife). Some PCBs burn so easily (even with a hot-air gun) that they are just not worth the trouble. I'm much more selective these days, though I'll still remove resistors that are easy to get out and are at the standard 0.5 inch spacing. As a result, I have pretty well any resistor value I need with pre-formed leads, which is handy when I'm building my hobby projects.
Most of the parts I use are through-hole, and most boards nowadays are almost totally populated with surface mount devices (SMDs). I personally don't do a lot with SMD components, although they are usually easy to get off using the hot air gun on the component side of the board (which in this case I place horizontally). There are certainly lots of fairly tasty switched-mode power supply components to be had. Also, I recently purchased a bunch of Adafruit's SMD adapter boards, which make it very easy to use SMD ICs on a standard breadboard or through-hole PCB. SMD components -- especially transistors and diodes -- usually have fairly cryptic markings on them; if I can't identify them as something useful, I tend to leave them alone. A pair of SMD tweezer probes (as shown below) is really handy for quick-sorting SMD parts, and even small through-hole components.
Although my acquisitions from old PCBs (along with my natural hoarding instinct, which drives my wife nuts) mean I have just about anything I need for building up a project without going to the store or mail-order, I have to be careful when using these parts. On occasion they don't work, so a bit of time testing components that are going to be soldered in before I do so is well worth the effort.
I have a transistor tester I built when I was about 16 years old that still works fine. It comprises a 1.5V battery, a tuning meter from an old radio in series, and a 500K potentiometer, which feeds the battery to the base of the transistor. You turn the pot so that the needle of the meter gets to a certain point, corresponding to an IC of 1mA, and then read the Hfe value off the scale of the pot. You can work out the base current Ib from the pot resistance across (Vbatt - Vbe) = (1.5 - 0.6 = 0.9V) and work out the Hfe from Ic/Ib when you calibrate it. This is not real high-tech stuff, but it is incredibly useful. My Fluke 8050 desktop DMM (now around 40 years old and still going strong) had instructions in the manual to build a transistor tester attachment, which I did. I also built a capacitance meter from a couple of 555 ICs, and I have also bought a LCR meter now. What I'd really like is a 74 TTL / 4000 CMOS tester, as I get -- and use -- a lot of those ICs.
Along with my board-mounted bits, I have amassed a lot of other things like meters and switches and relays and connectors and displays and stepper motors and... I use these occasionally and, as I mentioned above, it's really handy to have them to hand if I need them, but I seem to amass more than I can ever use unless I go into production. I work on the theory that if anything is useful, I'll keep it. On the other hand, if someone wants something I've got, I'll happily give it to them if they can find a use for it.
