replacing transistor on multi layer boad

Discussion in 'Technical Repair' started by xtal_01, Jan 3, 2019.

  1. xtal_01

    Thread Starter Member

    May 1, 2016
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    The farmer next door has a telescopic man lift that stopped working. He asked me to take a look.

    He pointed out the main control board on the basket ...hmmmm micro processor ... discrete components ... looking at the dates probably 40 years old. When I asked what happened he said .... the red light (LED) on the board would go out and the unit would stop working, I would push on a black part and it would start working. The black part did get warm. Then the black part broke off and now it does not run.

    WOW .... why no call me when it started to give you problem!

    OK, so I pulled the board. I found the "black part" in the bottom of the enclosure.

    The part is a MPSA06 transistor.

    I think it may have just broken off the board as he pushed on it so many times.

    It may have had a loose connection ... or a broken lead .... or ????

    So, I do not have a rework station. I was about to just put my iron to the board and try some solder wick or my spring loaded sucker.

    Then I started thinking will I do more damage then good? I have never made a repair on anything but a double sided board. This is a multi layer board. I am already hoping he has not broken one of the traces inside the board.

    Do I take a shot at repairing this or is there places that specialize in repairing these boards?

    The manufacturer said they will not touch it (tried them first). The original board is obsolete. The replacement board is over $2K ... he paid less then that for the machine so he does not want to put that kind of money into a board ..... he is a typical rural farmer, run your equipment into the ground.

    I am not an electronics guy. I build control panels ... literally just wire plc's, switches, lights, etc. into a package .... no board level repairs. I "play" with electronics as a hobby only.

    Any advice would be greatly appreciated.

    Thanks .... Mike
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
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    I've removed through hole components from boards with as many as 8 layers and it's not unlike working on a board with 2 layers. Having ground/power planes on internal layers could require a higher wattage iron.

    He has nothing to lose with a repair attempt, but you should make sure you're up to the task. If you doubt your abilities, find someone with experience to remove the part.

    A technique that some find helpful is to cut the leads to remove the component body and then remove the leads. Then you can try to melt the solder and pull the lead out with pliers. If you do this, don't use excessive force because you could pull out the plated through hole. On a multi-layer board, that could be game over unless you have a schematic that would let you find and repair broken inner layer traces. You could use solder wick or your spring loaded solder sucker to remove any solder remaining after removing the leads. Or you could use the wet toothpick trick to clear the hole.

    Don't use too much heat because the adhesive will release and pads/traces will be easy to lift.

    One other thing you could try after removing the component body (make sure you note the orientation - maybe with a picture), but before removing the leads is to tack a replacement to the leads and see if the board functions. If it works, that probably eliminates the possibility of broken inner layer traces.

    To reiterate. Temperatures high enough to melt solder could be enough to allow pads/traces to be lifted by friction from solder wick (particularly if the solder solidifies before you get the wick removed) or suction from the spring loaded remover.

    If you post pictures of the repair area, members might be able to give you tips on where to position the iron and the remover. Personally, I'd use a vacuum solder remover because it's easier to suction the solder. With a spring loaded remover, the time required to remove the iron and position the sucker could be long enough for the solder to cool down. With a vacuum tool, you activate suction when you see that the solder is sufficiently melted; I make sure I can move the lead easily in the molten solder before I pull the trigger to activate the vacuum.

    Personally, I'd avoid solder wick. You can't see the state of things under the wick and it's easy to lift a pad/trace when you can't see that it's loose.
     
    Last edited: Jan 4, 2019
  3. DickCappels

    Moderator

    Aug 21, 2008
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    Go with the solderwick. I have had very poor luck with a solder sucker, even tearing a trace off because of the kick-back. An added advantage of the solder sucker is that you can keep the soldering iron on the board so it doesn't have a chance to cool down as it would when switching from soldering iron to the sucker.

    Remember to flux and prime the solderwick for best results.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    If the broken leads on the board from the transistor are long enough, you might be able to just solder the new transistor to the old leads.
    That would minimize the chance of damaging the board.
     
    AlbertHall likes this.
  5. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Yes, I like this idea for this circumstance.

    BTW, the original intermittent contact may not have been the 'black part' itself but could have been (could still be) somewhere else on the board. Pressing the 'black part' flexes the board and could 'fix' a bad joint elsewhere on the board.
     
  6. xtal_01

    Thread Starter Member

    May 1, 2016
    50
    8
    Thanks for the advice!

    I will have to give this a little thought this weekend. I did find a shop that said they would fix the board for $300 ... seems a bit steep but then I am sure they have a vacuum pump rework station and you are really paying for their knowledge.

    I "think" I can do the repair but am just afraid of killing the board (if it not already dead).

    Thanks .... Mike
     
  7. dl324

    AAC Fanatic!

    Mar 30, 2015
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    You can try tacking the replacement part to the original leads. That wouldn't risk additional damage. Just make sure the replacement is installed in the correct orientation and that the joints are appropriate for the current.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Are you sure that the 40-year old PCB is multilayered? I would think at in those days they had not moved beyond double sided boards.

    A photo of the PCB and the area under discussion would be helpful.
     
  9. xtal_01

    Thread Starter Member

    May 1, 2016
    50
    8
    The transistor sat right on top of the LED at the lower right corner.

    I have removed the board and the potting material around the area (some kind of soft waxy plastic ... not epoxy).

    I will try to post a better picture of the area when I get my camera back (lent it to the neighbor).

    I know the board is multi layer (or at least I think it is0 as there are components with no traces going tho them on the top or bottom of the board (so I assume the traces are within the board).

    The board is very thick.

    The manufacturer would not help me at all with the schematics ... obviously wanted me to spend $2K on the new board. They said it is their policy not to work on boards older then 5 years.

    Thanks .... Mike
     
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  10. Duane P Wetick

    Senior Member

    Apr 23, 2009
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    You may be able to effect a repair...but I doubt it. The newer Electronic controls are basically un-repairable by pcb repairers...however an underground re-programming service industry exists for many med to high volume controls. Its up to you to do some gumshoeing and find out where and who they are.

    Cheers, DPW, Spent years turning op-amps into heaters.
     
  11. xtal_01

    Thread Starter Member

    May 1, 2016
    50
    8
    Had another one come it today ... bad HDIM port on a laptop computer. The guy said he watched a you tube video ... all I needed to do is to unsolder a surface mounted connector and put on a new one.

    Never have I touched a surface mounted part. I sent him to a computer repair shop ... they will send it away and fix it for $300 ... probably more then the computer is worth.

    Mike
     
  12. dl324

    AAC Fanatic!

    Mar 30, 2015
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    If it wasn't under warranty, you're right - probably not worth repairing. You can buy a decent new laptop for $300-400. You can buy a decent used laptop for a couple hundred.

    We've become a throwaway society because labor costs are often a significant portion of the cost of a new replacement.
     
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  13. absf

    AAC Fanatic!

    Dec 29, 2010
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    You mean this transistor?

    SMD MPSA06 resize.PNG
    Shouldn't be too tough to remove and replace with in a new one.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    I think it's more that the labor cost to repair a part is now much more than the automated mass-production cost of a new part.
    The reason you repaired an old standard-def 25" CRT color TV was that the hundreds of discrete parts in it were all wired by hand, so it cost perhaps $5000 or more in today's money, thus generally making it much cheaper to repair than replace, even if it required something as expensive as a new picture tube.
    Now they can manufacture a flat-panel 55" HD color TV that sells for $400, so it's not economic to fix it for any but the most simple of failures.
     
  15. xtal_01

    Thread Starter Member

    May 1, 2016
    50
    8
    Yes, that is it.

    I guess the thing is, if it was mine I would repair it. I am always afraid of touching something that belongs to someone else.

    If I kill that board (even just getting it too warm and pulling the trace off the board) then I would feel responsible. If it was a few hundred dollars I would say take a chance .... at $5K .... let an expert do it.
     
    absf likes this.
  16. dl324

    AAC Fanatic!

    Mar 30, 2015
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    It was suggested that you tack the new device to the existing leads. Is that not being considered now?
     
  17. xtal_01

    Thread Starter Member

    May 1, 2016
    50
    8
    I was going to but the one of the leads broke off right at the board.

    I might have gotten away with it but again, just didn't want to take the chance of messing up the board ... this I had him send it to a repair facility who does this stuff all the time.

    fore $300 ... a lot better then me killing his board.
     
  18. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Removing solder from the one that broke off shouldn't have been difficult. There's always the backside part of the lead.

    But, better to be safe than sorry. If you didn't think you could do it without causing more damage, having him pay someone else to do it was the right thing to do.
     
    absf likes this.
  19. MrChips

    Moderator

    Oct 2, 2009
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    btw, that is called conformal coating.
     
  20. xtal_01

    Thread Starter Member

    May 1, 2016
    50
    8
    Interesting ... till now, I have seen 1) nothing 2) epoxy 3) silicon ... never saw anything like this before.

    Thanks!
     
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