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How to safely get PCB out of old amp/preamp/receiver chassis

Discussion in 'General Audio Discussion' started by EJB14, Jan 12, 2018.

  1. EJB14

    EJB14 Member

    Messages:
    77
    Location:
    WA, USA
    Hi all;

    I am new to the restoration/repair of equipment and one thing I keep running into is - do I de-solder all the wires connecting the PCB to the power supply/chassis/other boads etc so I can work on it or leave 'em soldered and work on the board in place?

    I have found that the way I like to work is to do a little, test, do a little more, test, etc. - but when I remove a PCB it exposes problems with that methodology. Un-solder too many times and the trace/board starts to de-laminate. Work on the board in place and I have touched wires or things I don't want to touch with the iron by accident. Looking for a better method if there is one.

    Recently I've run into a power connection on the NAD 1700 that uses the wires tightly turned on posts in the PCB. I am tempted to just un-solder to remove the board, but perhaps there is some kind of replacement I can use so I don't have to un-solder anything (like replacing the posts with a plug of some kind).

    Any ideas?
    Thanks!!
    -Ed
     

     

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  2. OMGCat!

    OMGCat! AK Subscriber Subscriber

    Messages:
    3,137
    Location:
    El Sereno, CA
    You will pretty much have to pull some boards but you're right that you don't want to keep pulling and then re-soldering to check.
    If you can't access the bottom of a board or something without de-soldering then you have to be meticulous when replacing parts. Lots of good reference photos and replace part for part so you don't get confused. Once done and ready to go back you'll be confident that it should work.

    I try my hardest to work around wires and what not so I don't have to de-solder pins. If you slow down and be very careful you can work close to other wires and such without causing damage.

    It's possible that you'd be able to replace the pins with a header plug or something but then you're adding another failure point where the two connectors meet. Some amps did have boards with wire connectors and others with edge type connectors like game carts so it's not unheard of.

    Welcome to AK BTW!
     
  3. restorer-john

    restorer-john Addicted Member

    Messages:
    6,409
    Location:
    Australia
    Hi Ed and welcome to AK! :)

    De-laminating or lifting of PCB tracks is generally a combination of too much heat and spending too long on the joint. With normal 60/40 solder, around 350 degrees C or 660 farenheit with a dwell time of 1-3 seconds should be fine for the majority of desoldering/resoldering of small components.

    That said, there are some PCBs in vintage gear where lifting of tracks is common, especially around heat producing or heat affected parts. Get yourself a really good solder sucker or desoldering station. Wick is not a good option if you want to keep your traces intact. I haven't used wick since I was 8 years old and bought my first sucker- then moved on to desoldering stations. I don't think I've had a lifted trace (one I did) now for as long as I can remember.

    Until your soldering improves (or you buy a nice temp controlled station) with a decent 60+ watt iron on it, I would continue to use the 'little-test-little more' strategy you are employing.

    Most of the time, unless you have extra wire length to play with and a wire wrap gun, we all tend to leave wire wrap posts alone. That said, sometimes choices have to be made to remove entire wrap posts along with the wrapped wire. We simply resolder the entire pin back in after the work is done. The preference is to use excess loom length to manipulate the PCB into a position where the work can be done and minimise the rotations of the board to prevent wire damage.
     
    Last edited: Jan 12, 2018
  4. mac mini

    mac mini Active Member

    Messages:
    270
    That's a nice answer to a good question. Is there a particular solder sucker or desoldering station that you recommend? Also, how do those Royal Grenadier Speakers by Empire sound?
     
  5. restorer-john

    restorer-john Addicted Member

    Messages:
    6,409
    Location:
    Australia
    For low cost, these two manual ones from the Japanese Engineer brand are great :

    http://www.engineer.jp/en/products/ss01e.html

    Also this one from Goot is excellent. Do not be tempted to buy chinese copies of this- some work, some don't.

    http://www.goot.jp/en/suitori-rework/gs-100/

    For good stations, there are all sorts of low cost ones out there that are ok and some that are crap. I would suggest buying local, where you can get filters and tips easily. A hobbyist just starting out doesn't want to spend $1k on a station.

    PS the Empires are actually packed in their original cartons in storage. I need to rebuild the midranges...
     
  6. EJB14

    EJB14 Member

    Messages:
    77
    Location:
    WA, USA
    Thanks for the welcome and great responses everyone! I will start aiming for a dwell time of 1 to 3 seconds. Sounds about right. So far have only de-laminated one trace, and that prompted this post. Fortunately I caught it in time and was able to still repair it.

    I am using a Weller WES51 station for the soldering work, and have it set at 650 degrees. It is great for me, but yes, while solder wick does good, a really good solder sucker (or station?) is on the list. I bought a number of cheap plastic ones off Amazon to use with the Weller with mixed results (the conventional cheap tube with a button). I recently bought one that is an iron/conventional sucker that I got for $10 (https://www.amazon.com/gp/product/B00B88FRME/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1), and it works, but it takes *forever* to heat up, and I don't like leaving it on the solder/PCB so long. It takes about 10 seconds to be 'ready' to press the button.

    Thanks restorer-John for the links - so I guess you are suggesting for the cheaper route, using the good solder station and a decent manual sucker instead of the cheap iron/sucker combo unit. I will check those out..
     

     

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  7. OMGCat!

    OMGCat! AK Subscriber Subscriber

    Messages:
    3,137
    Location:
    El Sereno, CA
    I use a Hakko 472D desoldering station and love it. It makes desoldering even easier than regular soldering.
    You can typically find these used for about ~$100 on eBay and they'll likely need the $100 maintenance kit you can buy on the Hakko website. Just make sure it has the iron/gun part. If that's missing it's not a cheap prospect anymore.
    If you're only planning on going into an amp now and then I'm not sure a big, several hundred dollar apparatus is a good investment of your money but if you end up doing more regular work it's worth looking into.

    I used to live in Tacoma, this is definitely a great time of year to be inside doing projects.
     
  8. orsen

    orsen just another old cheapskate that likes audio

    when i saw the title, i thought, wow! stereo with deadly transformer, :crazy: me
     
    merlynski and gtv2000 like this.
  9. EJB14

    EJB14 Member

    Messages:
    77
    Location:
    WA, USA
    Yeah - there is that too (not electrocuting oneself with all that power).
    Searched for the 472D on Ebay - nothing showing up yet, at least not in that $100 price range, but this Hakko looks interesting on Amazon new for $245 - the FR300-05/P.
    This has been very helpful - thanks again!
     
  10. fred soop

    fred soop Super Member

    Messages:
    1,990
    You can replace the difficult to disconnect pins with test point terminals. Here is one from DigiKey and they are available in all the standard colors.

    https://www.digikey.com/products/en/test-and-measurement/test-points/616?k=5001k

    Then the wires attached to the board don't have to be tightly squeezed on pins. They can be loosely looped through the terminal and held by a bit of solder. Very easy to disconnect and reconnect multiple times with minimal damage. Another option if you know that you will be doing a lot of work is to splice extensions to all the leads and have the board wired but physically separated from the rest of the unit.
     
  11. Markoneswift

    Markoneswift Quartz locked n ready to rock

    Messages:
    3,394
    Location:
    Aotearoa New Zealand
    Totally understand where you're coming from @EJB14

    I too am a relative newcomer to the world of audio repair (well to all electroinc repair, actually) and I know your frustrations ! I really do favour the units which have removable bottom covers or such like and often, I will pass on repairing a unit that I know is going to be a pain in the a$$ just to get a resistor out of (which is just about all home theatre receivers ever made in my experience).

    I also leave wire wrapped posts alone - the tool to redo these is not cheap (at least, it isn't here) but they do make handy test points too for checking voltages etc.
     

     

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  12. EJB14

    EJB14 Member

    Messages:
    77
    Location:
    WA, USA
    Thanks Fred! I will definitely check that out..
     
  13. fred soop

    fred soop Super Member

    Messages:
    1,990
    Another solution is to work completely from the top of the board. Cut the leads as close to the part as possible, hopefully leaving enough of a stub sticking up from the board that the new part can be spliced. Not quite as neat, but it does work.
     
  14. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,751
    Location:
    Southern NJ
    Hakko 808 for me, but any vacuum desoldering machine that gets hot should do the trick. If my 808 died tomorrow I'd probably replace it with whatever the current Hakko model is. Not so much married to the brand but I've been satisfied with the things I have purchased from them. If I found a different brand that was as good or better for a comparable price I may go that way.

    I try to not remove boards unless there is no choice. I work from the bottom, or unmount and move things around for access. I've rebuilt boards hanging in space from their leads more than a few times. Disturb as little as you possibly can.
     

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