"Old" electronic components

[jetsam]

I enjoy disassembly for its own sake as well.  I used to hate difficult salvage of multi-legged components, but I got a cheap Velleman soldering iron/sucker which works better than I was expecting it to...  now I quite like the challenge of a USB connector or a 6 terminal transformer.

On the list for Xmas wishes: hot air and surface mount salvage gear.  Do you have any recommendations in the cheap-as-can-be range?  I'm thinking a cheap-*** Chinese clone rework station, maybe a hot plate, some thermal protection for me (full ski mask style eye protection and oven gloves(??)), and a second fire extinguisher for the area...

Have you been able to salvage and reuse surface mount chips of modest size?  I'd like to be able to use the 6 to say 32 pin jobbies in other projects with breakout boards at first, maybe pcb's later...

cheers,
jetsam

[SilverSolder]

There is definitely something pleasant about recycling electronic junk...   sadly, you end up with an even larger collection of parts that you then end up using <5% of!  :-)

It is indeed good practice to measure components on junk boards (both in and out of circuit) to develop your "feel" for how things are supposed to work.

[GlennSprigg]

Having a special value resistor in the sensor seems a bit silly, a 50 cent pot can be any value resistor you want and a multi-turn trimmer can be set quite accurately.

Yes, but you need to know the value first!! 

Measure the voltage across the sensor? I don't know a lot about alarm systems but even if they used ordinary off the shelf resistors you'd still have to know the value.

Hi James....  I think you missed the original point, so I'll explain 
For those more elementary alarm systems, the equipment manufacturers tell you, and 'give' you, the custom
special value EOL resistors, and values. This simplistic 'method' was only a basic deterrent to stop people
from 'trying' off-the-shelf resistors, to bypass the circuit. We only had to make our own, if we didn't have one
handy, and we 'know' what the expected value is for that particular alarm panel. They had quite a small
margin for error!! Slightly too high resistance signals an alarm. Slightly too low causes a Tamper alarm.
(The circuits are normally-closed (with resistor in series) for a no-alarm condition).
Have a great day. Glenn

[james_s]

I enjoy disassembly for its own sake as well.  I used to hate difficult salvage of multi-legged components, but I got a cheap Velleman soldering iron/sucker which works better than I was expecting it to...  now I quite like the challenge of a USB connector or a 6 terminal transformer.

On the list for Xmas wishes: hot air and surface mount salvage gear.  Do you have any recommendations in the cheap-as-can-be range?  I'm thinking a cheap-*** Chinese clone rework station, maybe a hot plate, some thermal protection for me (full ski mask style eye protection and oven gloves(??)), and a second fire extinguisher for the area...

Have you been able to salvage and reuse surface mount chips of modest size?  I'd like to be able to use the 6 to say 32 pin jobbies in other projects with breakout boards at first, maybe pcb's later...

cheers,
jetsam

With hot air it's trivial to remove surface mount ICs with hundreds of pins, I've salvaged 208 pin QFPs with a heat gun but a proper temperature controlled hot air station is better. I usually do the removal with hot air and solder them with an iron and flux.

A vacuum desoldering gun makes through-hole parts easy, I can remove 40 pin DIP ICs from a double sided board on a whim in a couple of minutes.

For salvaging parts from a scrap board I've often used a heat gun, the sort used for stripping paint and thawing pipes. Set the scrap board upside down over the bench suspended between a couple scraps of wood, heat an area of the bottom with the heat gun and then whack it with a stick and parts will rain out of it onto the bench. It's brutal and smelly but fast and efficient. Make sure you have good ventilation and try not to cook the board so much that it burns and stinks.

[Dacke]

On the list for Xmas wishes: hot air and surface mount salvage gear.  Do you have any recommendations in the cheap-as-can-be range?  I'm thinking a cheap-*** Chinese clone rework station...

If you're talking about the cheap hot air stations in the $35-$65 range that all have the same design but dozens of different brand names on them,  those things scare me.  I've probably seen half a dozen videos over the past year of those things just sitting on the bench not being used and randomly having a complete meltdown,  over heating and catching fire.  Some people may have great experiences with them,  but I just don't want to risk something like that happening in my home especially if I step away from the bench for a bit.  I can't afford a professional rework station either,  so I compromised and bought a Quick 957DW+ rework station about a year ago,  I think I paid maybe $110 for it new from Digikey but I still consider it a cheapo station.  But even with this one,  I still think about it spontaneously just going up in flames so I always keep an eye on it if I'm using it.  This all could be just my paranoia though.