Scavenging parts more 'efficiently' - Page 1
Forum section: electronics / general

author: h4x0r
author_rank: Contributor
timestamp: December 18, 2019, 04:49:25 am
content: Dear Experts & Professionals,I'm not one of you, but I seek your counsel.I am scavenging parts from old gear I own and have obtained, be it through-hole or smd.Everything from old valves to smps bought in job lots.The issue I am facing is the purchase of a new/used hot-air / rework / dedicated desoldering station or combo.I do not know much about what is the current "best bang for buck" gear for this purpose. At the moment I have various manual equipment ( I am not a pro) which achieves the task- slowly... such as heavy duty soldering irons (superscope) and desolder wick, manual suction guns, and a cheapo chinesium rework station (some jaycar branded junk bought years ago) which has an aquarium diaphragm pump in it.. so naturally you'd understand it's been rather "useless" for a lot of smd removal 'attempts'. It's OK for heatshrink tubing and that is about it.I want to step my desoldering game up. I need to be able to pull desirable through-hole and smd components from dozens of boards I have laying around to fill my parts bins.Ive seen this "quick 861dw" hot air station on a bunch of reviews and various YT channels. It looks decent and ok value for money. But I don't know if it's true marketing BS or how they have lasted.I'm not sure that I can afford new Pace or JBC metcal etc. and the australian distribution/sales for a lot of the "decent" brands here leave a lot to be desired in pricing when dealing with small customers. It seems they are only interested in global-corporate bulk purchase orders.Because of this my choice instead has been to look on banggood / aliexpress / ebay / amazon etc and find something that's actually useful which will be of decent quality and last long enough to be worthwhile isn't the easiest task either. I'm hoping someone here will chime in with some advice or recommendation.I would like to get access to Taiyo (goot) equipment here, but I have found there is no distributor for the electronics division (sulzer are distributors for the other Taiyo industries divisions). I have a few of their goot branded soldering workstations and rate them highly. But have no access to their combo svs stations or kits, or vacuum pump desoldering guns.Longterm I'm obviously looking to use the gear to further my own usefulness, but it's not for commercial/business use. This is obviously the primary reason for asking what "works" but is properly decent enough for the professionals out there to use on a daily basis.Obviously what I am doing now is not efficient. It's also cumbersome. So any recommendation on a good hot air rework and vacuum desoldering station (or combo is a ++) would be much appreciated.I'm not opposed to spending money on good quality - but it has to last, and represent some modicum of value for money. I do not see JBC or Pace or Metcal etc as representative of that, based on our local distributors pricing, and will not touch anything made by hakko (multiple bad previous experience).If you know of a good deal on a particular brand of rework/desolder gear or can recommend a brand that has served you for a similar purpose and been reliable please let me know. (NB: I'm 240Vac)Thanks in advance.

author: bob91343
author_rank: Super Contributor
timestamp: December 18, 2019, 07:06:47 am
content: I have owned a desoldering station for years and like it. It's a Chinese model, I think either 878 or 8878 and wasn't expensive. It came with a few tips and I bought more. The temperature and air flow are precisely adjustable.It's amazing how you play the air over a big chip for a few seconds and then the chip falls off the board. It won't overheat the parts if you are careful.I have desoldered switches, pots, capacitors, ICs, connectors, lots more.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 18, 2019, 11:39:17 am
content: Quote from: h4x0r on December 18, 2019, 04:49:25 amNo it isn't. The issue you face is how to store and catalog the scavenged parts, in order to be useful for projects.And this is an issue because THERE IS NO WAY this can be done efficiently, in any reasonable amount of time and space.Speaking as one who has been grappling with this problem for many decades.Look, I _like_ scavenging parts. It's a good way to relax. I use a combination of soldering iron and sucker, hot air gun, and 'big copper bar with gas flame heating.' A few hours scrapping a pile of old power supplies or whatever, results in nice piles of power FETS, diodes, bridge rectifiers, inductors, etc. Then what? You _could_ try stocklisting all the part numbers and searching for data sheets. Which will take longer than the desoldering. But you will only ever use 0.00001% of those parts, so it isn't really worth the effort in any practical sense.Another way is to buy some big plastic storage crates with lids (or just fruit boxes), and just store the original circuit boards. If you have space for a pile of such crates. Then when you need something, hunt through the crates, and only desolder that needed part. Most of my 'random scrap parts stock' is in that form, in boxes in a (sort of) garden shed.Only bought new parts and 'found bulk old stock' parts like ICs and transistors deserve any kind of ordered storage by part numbers.

author: bob91343
author_rank: Super Contributor
timestamp: December 19, 2019, 05:35:46 am
content: Terra, you hit the nail on the head. I am swimming in scavenged parts. Now and then, albeit rarely, I have something I need for a repair or project.Still, it's good therapy for me to disassemble stuff, and when I look over my stock of parts I am reminded of how much good stuff I have. Just in case.When someone on Craigslist offered a box of components I grabbed it. In it were not only lots of resistors and capacitors but thousands of 1N4148 diodes. I give them in sacks of 50 or 100 as gifts to friends. They make good temperature sensors or rectifiers and I clip off leads if I need a short piece of wire. I still have perhaps 5000 diodes. They aren't worth much, maybe a penny or two, but at least I won't ever have to buy one again.

author: Berni
author_rank: Super Contributor
timestamp: December 19, 2019, 06:36:05 am
content: Yeah scavenging parts is mostly fun in the sense of going "Woho free parts"But much of the stuff is never reused and just becomes a hard to sort trough pile. I tended to just pull off parts that have reasonable value and are easy to get off. So i never went for desoldering chips or anything (Unless i had something in mind for the chip).Some of the things i did like to pull out are power semiconductors on heatsinks (having heatsinks with already threaded holes including screws, nylon washers and silpads included is really useful), rectifiers, relays, ferrite ring cores, IEC mains plugs (Especially ones with filters), large film caps, switches, motors... Another thing i liked to keep are PC ATX power supply cables since i could easily clip them off and throw them in a box for when i need some short colorful wire to wire some things together.These days cheap chinese electronics targeted at makers are feeding my parts hoarding. You can get a little board that does one thing (Like a DC/DC, battery charger, protection, USB to uart etc...) for from a few cents to a few dollars each with free shipping. These little modules are much more useful when actually trying to make something because it has the chip and all the required components already on it. Just give the little module power and it works. Really quick for throwing together a project over an afternoon, but you need to have the modules on hand due to the 3 to 5 week free shipping(but sometimes more like 10 weeks), so you need to stockpile all of the modules you think you might need in the future.

author: james_s
author_rank: Super Contributor
timestamp: December 19, 2019, 07:12:48 am
content: I scavenged lots of parts when I was a kid, it was the only way I could get a lot of stuff back then. Now I'm more selective, I scavenge stuff that's easily reused. LEDs are always handy, power transistors, rectifiers, ferrite and powdered iron toroids, nice heatsinks, that sort of stuff. I've sometimes used a heat gun like the sort used for thawing pipes.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 19, 2019, 07:46:00 am
content: Quote from: bob91343 on December 19, 2019, 05:35:46 amSounds like a nice hand-made diode ROM is in your future.Quote from: Berni on December 19, 2019, 06:36:05 amSpeaking of ferrites and other magnetics -- try to note where they came from, or what they were doing:- Common mode chokes are typically at the mains input, are 1:1 ratio, and have high permeability and low saturation. They make okay transformers, though the leakage inductance can be difficult.- Small power transformers are likely flyback supplies, often with a single-transistor (blocking oscillator) circuit, or a TNYxxx or other off-line regulator. The ratio and inductance will be suitable for whatever it was: the frequency is typically fixed and modestly low (~100kHz), the primary will be suitable for 120 and/or 240V operation, and the secondary will be suitable for whatever the output was. There's usually an aux winding on the primary side as well, which will be good for say 6-15V.- Alternately, they might be driver transformers, the tall ones from ATX supplies being a classic example. These are mostly used with BJT based inverters. These have complex windings (a feedback winding is included, which was coupling load current into the transformer -- positive feedback drives the BJTs), and aren't good for much besides what they did; you could maybe use them for small (< 10W?) flyback or forward converters, especially in push-pull primary and/or secondary configuration. The tapped windings give some opportunities for ratios (1:1, 2:1, 1:2, 1:+/-1, and a few oddball ratios when including the short feedback winding). The one isolated secondary (it's for the low side BJT by itself) also allows dual isolated outputs (with more limited options on ratios).Also kind of in this category, the triple winding toroid in CFLs. Same idea, BJT drive with current feedback. Probably high mu core.-Bigger power transformers follow the same scheme, but expect even more custom pinouts and windups, and pay attention to the configuration. You'll see 1-switch and 2-switch flyback and forward, half bridge forward and resonant, and sometimes odd things like self-resonant (usually half bridge) with saturable control (Sony used a ton of these in the 80s-00s, particularly with Trinitrons?). Expect oddball combo secondaries, like the ATX's +/- 5 and 12V windings. Or a whole bunch of outputs for monitors (typically something like 5V, +/-20V, 100V, and probably a few more).- Filter chokes, toroids, ferrite, the works: usually identifiable by being on the primary side (active PFC) or secondary side (choke-input rectifier, forward converter), in addition to a power transformer in the middle. If ferrite, these will be gapped to give usefully low inductance and high saturation current. If powdered iron, these will be... well, usually they're the ugly yellow-white or green-blue (#26 or #52) types, very lossy and suitable for low ripple fractions (and hence, average current mode control, or even more ugh, voltage mode control) at low frequencies (< 50kHz say). Other colors, and solid colors, are usually okay, but solid colors you can't really tell without taking measurements, there's no consistency on it. (Ferrites come in painted/coated styles, too!)That's what they were, by the way -- typical ATX supply with a TL494 or KA7500 or whatever in it, voltage mode control. Depends upon output capacitor ESR for compensation. This is why you don't want to repair them with super-low ESR caps, and why they go nuts as their caps dry out and ESR rises.You'll also see toroids in car power amps, usually a ferrite toroid for the charge pump. (It's mostly wired like a forward converter, but almost always lacks the output choke -- it's more of a charge pump, with the primary side switches dumping charge directly into the output caps, limited only by transformer leakage inductance, which is relatively generous at least. It's no wonder they are so prone to blowing up!)Ferrite beads, chips -- pretty generic. You'd have to measure Z @ F to see what they're good for. May be high or low frequency material; beads of course you can count turns (usually just one, the wire straight through), chips are multilayer so who knows. Multi-hole beads are usually good for quite some current, and high impedance (the complex magnetic path between all the holes allows it to saturate much more gently than an ordinary bead, which often saturates at less than an ampere).(Not that beads and chips are worth anything, and you can buy a sack of a hundred, or a thousand, of known type, for the labor cost of sorting them.)Although I take that back, there is this somewhat oddity:https://www.hitachimetals.com/materials-products/amorphous-nanocrystalline/surge-absorbers.phpparticularly the last couple pages. Saturable cores in ferrite-bead styles; hard to identify though, needs a pulse test pretty much.Saturable cores in general aren't that uncommon, despite how boutique they may seem -- it depends, but millions upon millions have been used, in ATX power supplies. Usually a stripwound core in a plastic box, with a few turns of heavy wire around it. This was used to regulate the 3.3V supply (using the power of only a TL431, and the property of the saturable reactor / magamp), which is constructed as halfway between a "2.5V" supply and a "5V" supply -- it was derived from the 5V taps on the power transformer, with one always on, and the other conditionally on, gated by the magamp. This way it could be varied between 2.5-5V (give or take), 3.3V being the set point.Other stuff; you'll find lots of neat but obscure power electronics in plasma TVs, mostly obscure because they were either: house marked, or poorly documented or custom-run parts (transistors, diodes, arrays), or custom arrays/drivers (ASICs, or probably hybrids/multi-die devices too). I've seen some transistors that were completely glued to heatsinks, no screw or clamp, no way to service them separately.The beefiest PDP parts are a few IGBTs for sustain current, typically rated 300-360V, and anywhere from 30A continuous to 600A+ pulsed. As far as reuse, these aren't quite as efficient as MOSFETs of comparable ratings, but you might make a cromulent power supply with them, or a modest sized Tesla coil, say.LCD TVs, monitors -- if the backlight is CCFL, can always take that out, separate it from the LCD panel itself, and use it as a light box or lamp. The supply is usually a push-pull BJT oscillator (somewhere between Royer and Baxandall, depending on how much supply inductance they provided, and exactly how the magnetics are designed). The output is high voltage and high impedance, suitable for igniting and operating, well, CCFL lamps, and maybe some other shorter discharge tubes (don't expect them to ignite regular length neon lights, but short ones, or stacks of regular fluorescent bulbs, sure). If LED, same idea, probably with a constant current buck driver, using a regulator or controller. If saving for illumination purposes, consider tracing for enable and brightness signals; hopefully it's analog and you can just slap on a switch and pot. Worst case, it's digital (SPI or I2C?), which may be documented in the datasheet, or if you can't find a datasheet (or it's all in Chinese or whatever), who cares, it was junk anyway!Tim

author: Terry01
author_rank: Frequent Contributor
timestamp: December 19, 2019, 08:45:42 am
content: I love stripping parts from boards! It's one of my favourite pass times and I've also learned a lot soldering wise along the way. Spare boards are great for practicing on too. I have one of the de-soldering guns similar to the one the OP mentions. It's not one of the higher end ones but it gets the job done nicely. I find cleaning it regularly helps keep it in good steed and you can also buy spare filters and nozzles cheap from Ebay or wherever.I use plastic tote boxes for keeping the spare parts in. They are about the size of juice or fruit crates and you can stack them to the roof

author: lowimpedance
author_rank: Super Contributor
timestamp: December 20, 2019, 02:12:13 am
content: @T3sl4co1l Tim that was a very handy post. Thanks for the effort.As for my scavenging habits I tend to stick to the hardware components such as connectors, pots, heat sinks, cases mains transformers etc etc and leave circuit boards intact until some part maybe needed, usually !.As stated though keeping piles of old 'junk' requires the storage space or highly developed tessellation skills.

author: aargee
author_rank: Frequent Contributor
timestamp: December 20, 2019, 05:54:43 am
content: Great reply Tim, but I have to ask - what is a "cromulent power supply"?

author: oPossum
author_rank: Super Contributor
timestamp: December 20, 2019, 06:18:17 am
content: Quote from: aargee on December 20, 2019, 05:54:43 amA power supply that has been embiggened to make it perfectly cromulent.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 20, 2019, 07:10:12 am
content: Cromulent: adj. mediocre yet adequate; average(It's a Simpsons reference)Tim

author: Shock
author_rank: Super Contributor
timestamp: December 20, 2019, 08:00:46 am
content: The most efficient way is not to spend hours on scrapping boards. If I have a board that has top quality capacitors I might remove them and perhaps some diodes, fuses, precision components, regulators what ever looks interesting.If the board is densely populated with usable components instead I'll add it to large box of boards that I have, otherwise it goes into the rubbish pile for recycling.The cheapest hot air going is a Chinese 858D station, these can be brought under $50.

author: bob91343
author_rank: Super Contributor
timestamp: December 21, 2019, 07:26:52 pm
content: I like my Chinese hot air station. It has earned its cost several times over. There is some learning to do but the hardware is great. Never had a failure, although the tips don't seem too secure. It can get dangerous if one falls off during an operation. I see that replacement heating elements are available but one needs to make sure to get the correct voltage rating.

author: andy3055
author_rank: Super Contributor
timestamp: December 21, 2019, 10:19:01 pm
content: It is fun to pull parts out of surplus gear. The problem is that very often what you need for a project is not in that lot you have harvested and you end up buying something new. At least, that is what happens to me most of the time