Tear Downs - Salvaging Electronic Parts

Salvaging old electronic parts is second nature to the DIY'er and gives the opportunity for learning. Also when the 'magic smoke' is released from an electronic component as is often the case when testing a DIY designed circuit (and not really knowing what you are doing, especially when you are starting out in learning electronics), it doesn't seem so bad when the bespoke electronic component was 'salvaged' in the first place (it was going to the garbage tip in the first place anyway! Right?).

Product teardown is actually a formal "thing" having a Wikepedia page which defines the process as "the act of disassembling a product, such as a television set, to identify its component parts, chip & system functionality, and component costing information". This "formal" process appears to be very close to "reverse engineering", and similar to the adage of "one man's poison is another man's wine", one company's "reverse engineering" is another company's "pirating our design". Anyway, for the DIY'er tearing down disused or junked electronic consumer products is an excellent source of components and potential learning how professional engineer's design and produce final products.

It is becoming increasingly difficult to identify components (due to "black blob components", repacking parts, parts with proprietary and or inhouse markings, etc) and SMD's are difficult to remove and reuse. However, if nothing else, wiring, crimped connector wires and the associated plugs/housings, and even the enclosure or housing of the chassis (which can be cut to remake a custom sized enclosure) can be useful.

In the lists below I have recorded pictorially some of my tear-down efforts, which may or may not be enlighting to interested readers.

There are also sections below giving tips on salvaging electronic parts and some information about component identification.

There are a number of basic tools that are required:

• Range of screwdrivers (flat head, phillips head, torx)
• Range of pliers (long-nose, flat)
• Wire cutters, metal shear (also to cut plastics)
• Soldering iron - desoldering pump and solder wick
• Multimeter - preferrably with L,C,R and transistor tester

Get a "system" for storing and labelling salvaged parts. The typical "junk box" approach (i.e., everything just thrown into a conveniently large container) is pretty limiting, as you will spend a lot of time "hunting through" this junk box and not really know what you may or may not have for a particular project. It is much better to have a series of containers that are labelled appropriately (e.g., capacitors, connectors, sockets, switches, motors, etc).

The actual containers in turn can be "salvaged" (or recycled) by just using food containers (e.g. plastic 2L ice-cream containers are my favourite, and not just because they use to store ice-cream which I was "forced" to consume in order to get the container!), cardboard boxes from various products, etc.

Have an old cloths iron that can be mounted hot side facing up onto which PCB's containing SMD's can be placed. The PCB is heated from underneath and from the component side (when hot enough) the SMD's can then be picked off with tweezers.

For those particularly fussed about working out "black blob components" and or with a penchant for "de-capping" and really finding out the internal secrets of IC's, the following link gives details about a decapping procedure (requires acids, so at your own risk) http://travisgoodspeed.blogspot.com.au/2009/06/cold-labless-hno3-decapping-procedure.html.

Again for those that are particularly interested, a "black blob component" is more correctly termed Chip-on-board (COB) apparently. From http://electronics.stackexchange.com/questions/9137/what-kind-of-components-are-black-blobs-on-a-pcb:

"the techniques is called Chip-on-board (COB). You do exactly the same to bond the die directly to the PCB as you would to bond the pins in an IC package. Savings: no package needed. (You could say no soldering also, but that has to be done anyway, so that's not really something you save on). COB is not cost-effective for small series, and with a few exceptions you will only see it on mass-produced products (100k~1M/year). The blob is an epoxy resin to protect the IC with the bonding mechanically; the bonding wires are very thin (as thin as 10μm for gold wire) and therefore extremely fragile. Another form of protection it offers is reverse engineering protection. This is not fool-proof (the resin can be removed), but it's a lot harder to reverse-engineer than simply desolder an IC.

Search for the datasheet if there is a part number listed on the IC package. I find the best site (which has lots of datasheets but little advertising) is http://www.datasheetcatalog.com/

Resistors

Resistors are generally not that useful to salvage as the 1/4W variety are readily available in multi-value packs at economical prices. Also, the wire leads have been trimmed and when salvaged generally do not fit DIY PCB's. However, large ceramic and high wattage resistors can be useful.

There are many sites online that give the colour coding scheme for resistors, so I will not reproduce this here. In any case, I find it generally quicker just to use a multimeter to determine the resistor value when removing, sorting and storing salvaged resistors.

Capacitors

Similar to resistors, capacitors are generally not worth salvaging (costs more in terms of your own time, electricity and solder wick) except for high value electrolytics. Problem is that the wire leads are trimmed, so difficult to refit and solder onto custom DIY PCB's. However, large value capacitance with high voltage rating capacitors are relatively expensive and worth salvaging.

Inductors

Transformers

Transformers are always worth salvaging, and are useful in DIY power supplies.

BJT Transistors

Small signal BJT transistors are generally easier just to buy (can get packets of 100 PNP/NPN BJT's for a few dollars from ebay suppliers). However, the large "power" transistors are always worth salvaging. Even if the transistors cannot be salvaged, the heat sinks are often worth saving.

MOSFET, JFET etc

IC's

The first stop for IC's is search for the datasheet if there is a part number listed on the IC package. I find the best site (which has lots of datasheets but little advertising) is http://www.datasheetcatalog.com/

If there is a datasheet, then the IC is potentially worth salvaging as at least you will know the function, pin assignments etc. If now datasheet, then basically not worth the time.

WARNING: No power should be applied while dismantling the consumer product, appliance, machine, etc and be particularly careful of any big capacitors (e.g., especially in microwave ovens) which could still have a charge (using a insulated handle screwdriver, short out capacitor terminals).

SAFETY FIRST: If you are going to dismantle a consumer product, best to wear gloves, eye protection etc.

Click on the following links to view individual tear-downs:

• Brother Inkjet Printer/Scanner DCP-J715W
• PIXMA Printer/Scanner MP780
• Simpson Front Loading Clothes Dryer