what's your thought about used components?

Discussion in 'General Electronics Chat' started by acdc100, Sep 29, 2011.

  1. acdc100

    Thread Starter New Member

    Sep 29, 2011
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    Hello I'm building my audio power amplifier. Probably use TDA7294 or LM3886. Audio capacitors must be used to improve the sound quality. I searched web and found there're many used components (audio transistor pairs, audio capacitors and ICs) which are disassembly from old boards. The prices are much much cheaper than brand new stuffs. I'm thinking of buy these parts for my project since my budget is very limited. Does any one has experiences in using disassembly parts? are they reliable?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    When I was a teen and learning electronics I depended on them. I still have no problems using old parts. Some, like electrolytic capacitors, are more likely than others to have problems.

    So (to me) what it comes down to is the project. Are you willing to develop troubleshooting skills when something doesn't work as planned. How humiliating will it be if the said project drops dead when showing it to, say, your girlfriend?
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    My thoughts are that many times you spend just as much messing with/troubleshooting/verifying used parts as you would to just buy new stuff.
    This is the same logic that prevents me from ever buying a used car.
     
  4. BMorse

    Senior Member

    Sep 26, 2009
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    I use salvaged components in a lot of my hobby projects since I usually have a very limited budget for them, so I usually salvage any components I may need from other devices and appliances, etc...
     
  5. tgotwalt1158

    Member

    Feb 28, 2011
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    There is no harm in that! In fact, these components are more reliable than new ones in some instances since most of them are salvaged either from high quality industrial or military products both of which have high reliability and MTBF. But, you should have some fascilty to check the vital components before soldering them on the PCB specially for important like graduate projects. For hobby projects, you could go directly without checking.
     
  6. saturation

    Member

    Dec 21, 2008
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    I use used parts all the time, one caveat, I rarely buy, often get for free, the whole boards or take apart the old device and do the salvaging myself. Folks who do it for cash don't care how they take the parts out, and overheating them can cause subtle damage to them that won't be noticed on cursory testing; you have to test those parts to their rated extremes. Many venerable used parts places like Apex Electronics in CA, often sell the whole boards, for just this reason.

    Many of the ICs from the 1980-2000 are also made better: they spent more time insuring the labels are very readable and the workmanship of the cases are impeccable so you can imagine what its like inside; compare say a 555 timer from the 1980s to one made today. Analogs are desirable, digital less so, but all well made. Resistors, inductors all nice, caps less so.
     
  7. tgotwalt1158

    Member

    Feb 28, 2011
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    Quite right! Just would like to add one thought which may be wrong, that military products are usually far ahead in time from their commercial counterparts both in quality and reliability. Once, a general told me that we disclose our technology for commercial use way too after it is already obsolete, that is decades after its advent, perhaps a good example would be wicky Leaks, just to emphasize my point.
     
  8. #12

    Expert

    Nov 30, 2010
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    I have hundreds of used components, and they are fine for doing a bench experiment, but I always buy new parts when I build a finished product. Might be peculiar to me, but I build 'em to last and have never had to repair anything I made from scratch.

    Incredible, but I have a thermostat that is still on its first electrolytic capacitor after 33 years.
     
  9. steveb

    Senior Member

    Jul 3, 2008
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    It all depends on where the parts come from.

    Were they taken out from a piece of working, but obsolete, equipment of reasonable age?

    Or from a circuit board that was plugged in with reverse polarity DC power, and scrapped as unrepairable?

    Or, from an ancient device that was operating long beyond its rated Mean Time Before Failure (MTBF)?

    Or, do you not know?

    I think it is ok to strip out parts that you know are from working devices of reasonable age and operating time. When you buy used parts from an outside source, do they certify anything that can help you determine how good the part is?

    There is more at stake than cost, time or embarassment. There is also the issue of safety, especially with electrolytic caps. Explosion and fires can require more than a little troubleshooting and resoldering to fix the damage, and the damage may not be limited to circuits and other property.

    On the issue of better audio quality with used parts, I wasn't aware of this issue, but if it's true, you can burn in your new parts in a controlled environment.
     
    Last edited: Sep 30, 2011
  10. saturation

    Member

    Dec 21, 2008
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    Yes, I would add that for myself too, I don't use the used parts for making devices for sale or for other people, or critical functions. They are all for prototyping or for myself.

    Yes, MILSPEC, and aerospace parts are the best! But finding the spec sheets on non-commercial parts can be a challenge.

     
  11. CraigHB

    Member

    Aug 12, 2011
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    I used to slavage almost all of my parts when I was a youth back in the days of discrete through-hole components. It was worth it then. I would have to make a trip to the local electronics shop and pay considerably for new parts.

    Things have changed 180 degrees. I can order parts online at very low prices from places like Mouser and Digikey. For example, years ago I used to pay like 50¢ for a single through-hole resistor at the local shop. Now I can get a strip of SMD ones for 2¢ each in quantities of 100 without leaving my house.

    Another consideration is that things are all SMD now so it's not as easy to salvage stuff. Though, there are some things that are still worth salvaging. I wouldn't say I never salvage anything.
     
  12. Adjuster

    Well-Known Member

    Dec 26, 2010
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    For a project which is going to be used for a long time and needs to be reliable, then scrap components may not be a good idea unless economics dictate that this is the only way to go. As already mentioned, certain classes of parts are not really worth considering, especially if they have had hard use: user-variable resistors and switches are a doubtful area as they may be physically worn out.

    One area where scavenged parts does come into its own is the repair of obsolete equipment, where new parts may simply not be available. Again, be discriminating: there is no point replacing bad with bad.
     
  13. monster_catfish

    Active Member

    Mar 17, 2011
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    Having purchased a couple of "Grab Bags", containing hundreds of linear and logic integrated circuit chips from Jameco Electronics, I got to wondering whether all those chips are used and pried off old boards, or, preferably, excess production runs of un-used parts that may have piled up in stockrooms for a few years.

    Anyone have any idea where Jameco Electronics sources the parts in those bags of miscellaneous ICs ?
     
  14. oldtech33709

    New Member

    Sep 24, 2011
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    You can look at the part leads to tell if they've been salvaged. Remove a part from aboard and compare those leads to an unused part. I think salvaging parts from boards is a great way to work on your soldering skills,
     
  15. Adjuster

    Well-Known Member

    Dec 26, 2010
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    As a youngster, I used to get parts from panels taken out of discrete transistor computers which were just beginning to come out of service at that time. Some of my elders gravely informed me that transistors removed and re-soldered were unlikely to work. They were mostly germanium, after all.

    In those days however, I few tools but good eyesight and fingers that worked properly. My methods (best not described in detail in case any of today's youngsters read this) would make a modern Health and Safety expert blanch, but the yield of working OC42s etc. was really quite good.

    One thing I learned early on is that it is no good to be too tentative about soldering. An iron tip needs to be small enough for the job, but not so small that it takes an excessive time to melt the solder, during which period the heat spreads and does mischief.
     
  16. steveb

    Senior Member

    Jul 3, 2008
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    Here is another thing that bothers me on principle. Yes, the prices of used parts are cheaper, but it seems to me that if you are going to put up with all the negative issues above, you would want to get those used parts for free. Paying for subpar stuff just rubs me the wrong way, especially when you can pick up obsolete equipment for free.

    As a comparison, I have a room full of brand new parts that I got for free. Literally millions of brand new parts, worth hundreds of thousands of dollars are in my lab, in my garage, right now, and I didn't pay a dime for them. I have friends that work at various companies and when they throw their obsolete parts away (yes, it happens more often than you realize!) I make arrangements to take them off their hands. The only condition is that I'm not allowed to resell them.

    Maybe you don't have those opportunities to pick up new parts, but old equipment gets thrown away all the time. Grab that stuff, get proficient at desoldering the parts (an art in itself) and then you have your free parts, as well as new and improved skills.
     
  17. Smoke_Maker

    Active Member

    Sep 24, 2007
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    Returned items, NOS, discontinued by that manufacture, etc. it's all good parts.

    There is nothing wrong with experienced parts, they already know how to do there job. :D
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    Electrolytic caps are the exception. Over time they stabilize to the voltage they are working at, and can't handle higher voltages well that was within their ratings. Many of the posts you read here will recommend changing these caps with new as a first step to reconditioning the board.

    Having said that, I would use them anyhow.
     
  19. monster_catfish

    Active Member

    Mar 17, 2011
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    Thanks for the good news, Smoke Maker.

    I did peer at the IC leads with a magnifying glass, and saw no signs of pervious use.
     
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