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Can I re-use old components?

Discussion in 'General Electronics Discussion' started by TTL, Feb 18, 2017.

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  1. TTL

    TTL

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    Oct 24, 2013
    I've had several projects which I've put away for a while and decided to complete now and am wondering which components I can continue to use and which ones I need to re-purchase. The components are probably 10-30 years old (from purchase date).
    Some components have been desoldered from poor PCBs (I'm re-etching the boards) and some are still in my component boxes, not soldered into anything since purchase.

    I've heard that electrolytic capacitors dry up, so I assume none of these should be re-used (desoldered or completely unused) because of their age), but how about these?:

    - resistors
    - potmeters and trimpots
    - ICs
    - transistors
    - diodes
    - ceramic capacitors
    - polyester capacitors
    - LEDs

    That's what comes to mind.
    I assume switches, connectors, IC sockets and such are fine as long as they're physically OK.
     
  2. Audioguru

    Audioguru

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    Sep 24, 2016
    I have many old electronic products that I take parts from. I do not re-use an electrolytic capacitor that has a bulged top and I do not re-use high power switches that have tarnished silver contacts that do not conduct low currents.

    I always bought switches and IC sockets with gold plated contacts for low power electronic circuits. The gold is thin so the cost is the same as high power silver contacts that do not work at low currents. Gold does not tarnish.
     
    Arouse1973 and hevans1944 like this.
  3. duke37

    duke37

    5,364
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    Jan 9, 2011
    I have repaired old valve radios 50 or more years old. Many of the components are OK.
    High voltage electrolytic capacitors will need reforming before use. Their working life is temperature dependent and modern ones are labelled with a maximum temperature. if run at a lower temperature, do not dry out so fast and they last much longer.

    Resistors can drift upwards in value.

    All components will have some corrosion on their leads and may be difficult to solder.

    AF117 transistors and their relatives have trouble with internal tin whiskers. I would not use these.
     
    Arouse1973 likes this.
  4. TTL

    TTL

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    Oct 24, 2013
    I had to look up the AF117 and it appears to be a "vintage" component, right?
    Nothing like that here. Only components from the 80s or perhaps earlier (2N3904, 2N3906, BF233C, BC212L etc).

    So it appears I should replace the resistors if I want to ensure they have the right values, and if I stay away from reusing electrolytic capacitors in general I won't have to do any guesswork. I assume, since noone has mentioned it, that other capacitors are OK to reuse?

    Talking about capacitors, I'm working on an audio project published in a 1980 magazine and it lists a variety of capacitors in its parts list: tantalum, polyester, ceramic, polycarbonate. When ordering, should I get those exact types, or has production evolved since 1980, making some of them obsolete or bettered by another type?
    And what about the capacitors in the parts list which have no comments about the type (along the values of 15nF, 47nF, 3.3nF, 220nF and so on)?

    The project mentions "2% metal oxide" for some resistors which I assume are more critical than others. Should I be looking at "metal film" instead these days?
    In other parts of the same project the resistors were listed as "1/4W 5%" -which types should I go for here?
     
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    The silicon transistors should be fine.
    Polyester, ceramic and polycarbonate capacitors should last forever. Tantalum and electrolytic capacitors should be replaced with the same types as the originals.
    15nF, 47nF, 3.3nF and 220nF are probably polyester type capacitors.
    Use 2% metal film for the metal oxide resistors and use the same power rating.
    1/4W 5% resistors are usually carbon film today.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
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    Jan 21, 2010
    It is unlikely that any of the resistors will have changed value significantly unless they are discoloured, however they're so cheap that it's probably not worth removing them for reuse.

    Electrolytic caps (certainly those of low value) are likely to be fine). Tantalum caps can go short circuit, so test them.

    Again, consider the cost of new components unless you're really good at desoldering and you're certain that the remaining lead length will be sufficient.
     
  7. TTL

    TTL

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    Oct 24, 2013
    Thanks (*steve*) and Audioguru. Useful advice!
    Actually I've desoldered just about all the components from the old boards for this particular project, but I think I'm going to take your advice and replace many of them except for the ICs, transistors, IC sockets, potmeters and other large/more expensive components.

    As for the "1/4W 5%" resistors which would be carbon film today -can I just as well replace them with metal film resistors at a higher tolerance (i.e. 2% as those other metal film resistors)? From what I've heard, carbon resistors are noisier than metal film, and this could be of significance in an audio related project I would think.
     
  8. Audioguru

    Audioguru

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    Sep 24, 2016
    If the input signal level is very low from a microphone, phono cartridge or tape head then use metal film resistors for reduced noise. For line level the tiny noise from carbon film resistors will not be heard.
    EDIT: Don't buy the parts from ebay.
     
  9. TTL

    TTL

    187
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    Oct 24, 2013
    Good to know about the low noise as I noticed the metal film ones cost quite a bit more.

    I knew you shouldn't buy semiconductors and capacitors on eBay because of fake/low quality components and such, but does the same apply to resistors as well?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If a part is critical, yes.
     
  11. Audioguru

    Audioguru

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    Sep 24, 2016
    I have a set or 480 carbon film 1/4W 5% resistors from Velleman (Belgian)?). The resistors have colors where blue and green, orange and red and yellow and brown are almost the same. The leads are thin and flimsy. Most have accurate values but some do not. They are made in China and have too much rice in them. I have seen much worse resistors in products.
     
  12. TTL

    TTL

    187
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    Oct 24, 2013
    Too much rice?
    Reminds me of the news a short while back where fake rice was revealed, which consisted of plastic!

    Where did you buy that resistor set?
     
  13. Audioguru

    Audioguru

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    Sep 24, 2016
    Did you see what this guy found inside a Chinese 18650 Lithium battery cell? Rice flour and a tiny little Li-Po battery cell.
     
    Harald Kapp likes this.
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