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September 30, 2020, 08:37:30 PM

Author Topic: Bonehead Mistake  (Read 665 times)

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Offline phigits

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Bonehead Mistake
« on: May 02, 2019, 05:13:55 PM »
Apparently reading all the instructions before starting wasn’t good enough to keep me from making a careless mistake. I have inserted and soldered (very well) the MJE5731A transistors facing the wrong way. The instructions clearly state to orient the metal tabs to the center of the board. I did exactly the opposite on one of the boards. De soldering a three pin transistor is proving challenging. Does anyone have any advice on how to loosen the transistors so I can flip them?

Offline HiFi Builder Guy

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Re: Bonehead Mistake
« Reply #1 on: May 02, 2019, 05:38:26 PM »
A solder sucker will to the trick: https://www.amazon.com/WEmake-WM-SP4-Solder-Sucker-desoldering/dp/B0002KRAAG << Just posting this one as an example not promoting  :D.

Alternately, if you have a good hot iron you could heat all three legs at once and gently wiggle it out. You have to be careful with this method though as you risk pulling traces from the board.
Shawn
HiFi Builder Guy

Offline phigits

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Re: Bonehead Mistake
« Reply #2 on: May 02, 2019, 05:48:09 PM »
Thanks - I have the same solder sucker as the link but it's not sucking all the solder out.  I'll try again to but it seems like the hole is so small, I can't get the sucker close enough to get all the solder.

Offline Tom-s

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Re: Bonehead Mistake
« Reply #3 on: May 02, 2019, 08:40:21 PM »
Desoldering wick will work.

Offline Raymond P.

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Re: Bonehead Mistake
« Reply #4 on: May 02, 2019, 09:12:44 PM »
I've never tried this myself, but it seem quickest if you could find another pair of hands and two more soldering irons.
Raymond P.

Offline Bonzo

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Re: Bonehead Mistake
« Reply #5 on: May 03, 2019, 01:47:54 AM »
Not so tricky.
I've used the wick lots of time. Be patient and take care not to overheat the board. It could take a lot, but it works.
Ciao
Bisogna avere orecchio!

Offline Deluk

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Re: Bonehead Mistake
« Reply #6 on: May 03, 2019, 02:39:55 AM »
Concentrate on getting the centre one loose. If you can get the majority of the solder removed you can use some pointed tweezers to wiggle the leg when the iron is applied to stop it sticking again. This might take some patience. When that one is loose you can work side to side to pull the other two out a bit at a time. Good luck.
It may sound counter-intuitive but it's often easier to remove fresh solder, so resoldering and starting over can often help when with a solder sucker or braid. A dab of flux can also be useful if you are able to do that.

Offline Paul Birkeland

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Re: Bonehead Mistake
« Reply #7 on: May 03, 2019, 05:10:34 AM »
Cut the MJE5731s off the board completely.  Heat each of the remaining pieces of MJE5731 lead in each hole one at a time and push it through with a toothpick.  Replace with fresh transistors.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Re: Bonehead Mistake
« Reply #8 on: May 03, 2019, 05:19:23 AM »
The way PB describes is how I do it too. It's less traumatic to the board traces to get each lead out of a pad one at a time.
Dan "Doc B." Schmalle
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Offline phigits

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Re: Bonehead Mistake
« Reply #9 on: May 03, 2019, 09:35:39 AM »
I did as PB and Doc recommended and just clipped the transistors and extracted the posts.  New transistors are on order.  Plenty of other things to work on while waiting.

Thanks to everyone who responded.

Offline EricS

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Re: Bonehead Mistake
« Reply #10 on: September 30, 2019, 05:31:01 AM »
I know that I'm late to this party, but I have a suggestion that might be useful to others as well.  I've done something similar a few times myself and I've always struggled with removing 3-legged parts.  The approach that I use now is to leave the original leads as long as possible, which leaves the transistor standing tall above the board.   If something goes wrong, the legs are plenty long enough to clip a probe to for measuring.  If I need to replace / reorient the part, I can snip off the legs down close to the PCB and have plenty of lead length left over to remount the device.  Maybe not a big deal with readily obtainable transistors, but some of the stuff that I use is no longer manufactured and getting difficult/expensive to source, especially if it is part of a matched set for a complimentary pair.
Eric

Haven't electrocuted myself yet...   
There are ALWAYS User Serviceable Parts Inside!

Offline adydula

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Re: Bonehead Mistake
« Reply #11 on: October 01, 2019, 06:21:16 AM »
Using solder wick can work well but if your not confident or have done this before the results can be less than you need.

When I use solderwick I slightly open up the braid AND apply some flux to the area I am gong to remove the solder from.

Using a flux pen or syringe you can easily apply flux to the area.

Then you need to apply enough heat quickly without damaging the part.

I watch for the solder to fill up the braid, if you use the correct heat it happens fast.

Getting the tip of the iron orientated the most efficient way is critical IMO...and to clean the tip right before dong this.

But with bigger parts the snip, and remove and replace is the way to go.

I remove pots by carefully destroying them or destructing them and then removing the pins one at a time...

Alex