Finding components from PCBs

[boic]

Hi Guys

Well I've spent the summer learning a topic I felt I needed to do for a long time.. programming and the use of microcontrollers and electronics. I feel inspired every time I see the potential and the future role in these things.. feels very liberating.

Well.. I've begun by buying a little arduino uno board and some components, but I had tons of old scraps of electronics laying around from older PC's we've had here and remote controls etc etc.. and I was wondering if I could rescue the components from these devices to use in my future projects I intend to make.

This raises the question I'm wondering of.. how do I know what values and types of components each SMD component is? I try reading and googling for answers with no results.. perhaps Im doing it wrong? I also take a magnifying glass to each component and try to read the little code on each thing.. they look like resistors and some I know are IC's.. perhaps some are also diodes too.. not sure. How do I go about finding out:

a) what these components are
b) the values that they hold
c) disasembling them from the PCB's they are soldered to

thank you 

[mariush]

It's hard.

Capacitors and resistors, diodes, you can measure with a multimeter.  Zener diodes are a pain in the ass, as it's hard to determine their voltage.

Some ICs... you can search the code written on top on Google and you get the datasheet. 

Small smt chips with just a few letters and numbers you may have some luck using sites like these:

http://www.marsport.org.uk/smd/mainframe.htm
http://alltransistors.com/smd-search.php?search=ab

The only other way I can think of is by searching for the service manual for that particular device (tv, radio, etc) and that service manual may say what each surface mounted chip is, or may say it's another chip than the one installed but at least you get an idea about what that IC is supposed to do (transistor, diode etc)

[Stonent]

Well here's an example video by Afrotechmods about regulators and he talks about how you can pull them off old circuit boards.



Basically if you're new to it, you'll want to get a soldering iron and a desoldering pump so you can melt the solder and suck it up quickly.  Braided desoldering wick also works.

For identifying parts it's something you learn over time but googling the part numbers helps.  Also Octopart.com is good for identifying things.

Here's an example of some kinds of capacitors:



There are a few other things that look like capacitors like:

Thermistors which are heat sensing resistors.
Metal Oxide Varistors (MOVs) these are used in power supplies to protect the circuit from too much electricity.

Transistors (Binary Junction and MOSFET):



Transistors can also look like temperature sensors and voltage regulators. So best to google the part number.

Resistors: Most have colored stripes on them. That can help calculate the value.



Diodes: (Usually have just 2 pins. Most will be black with white or grey stripe)



LEDs:  These are easy



Integrated Circuits: (You'll have to google the part numbers)



Voltage Regulators: Many begin with LM78 or 78 followed by the voltage (not always)

[Stonent]

If you really want a lot of scrap parts, check electronics parts stores for old circuit boards. I got one for $5 that came from some radio equipment that is loaded with all sorts of neat parts.  Also if you live in an area with a shared dumpster (like an apartment) look for people who throw away old stereos, vcrs and dvd players.

Fortunately there's a naming standard among most non-vendor specific parts so that makes it easier to identify.

A 7805 from Fairchild should be a drop in replacement for a 7805 from ST Micro.

ICs with 74, 74HC, 74LS are 74 series logic chips and are named in a standard way. There are also 4000 series logic chips which are also named in a standard way.

Chips with a dash and a number are usually indicating speed. Which would indicate the chip is a kind of memory or processor.
In newer chips a -10 or -15 is nanoseconds in much older chips -10 and -15 is tens of nanoseconds. In processors the number will usually be megahertz.  An 80386-33 would be a 33MHz chip.

Many chips that begin with 27, 28, or 29 are types of programmable roms. (PROMS, EPROMS, EEPROMS and flash)
Chips with endings of 32,128,512,1024 are a lot of times types of memory.

[juani_c]

A while back I made a post about identifying components, I used a motherboard. Perhaps you'll find something useful:
http://ssihla.wordpress.com/2013/03/04/recycling-electronics-component/

[tszaboo]

Also remember the component usefulness inverse law by me:
The more pins a component has the least likely you will be able to use it after you desoldered...
So don't waste your time on 20 pin ICs and stuff.

[mcotis]

Also remember the component usefulness inverse law by me:
The more pins a component has the least likely you will be able to use it after you desoldered...
So don't waste your time on 20 pin ICs and stuff.

I definitely agree with this statement!
I also find that a lot of the cheap components do not survive the desoldering process unless you really take your time; especially the older the components get.
Only use if you are really desperate.

[MirXas]

Old CRT TV's and PC monitors contain a good amount of re-usable parts, like voltage regulators, high power resistors, LEDs, chokes, cooling radiators and so on..

[nemo000111]

You can usually get some good parts out of power supplies as well.  As a rule, don't reuse the caps though.