Trouble replacing TR4 and TR5

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daniel_dlds
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Trouble replacing TR4 and TR5

Post by daniel_dlds »

Hi,

I am kind of new to this stuff. I am in the process of de-soldering TR4 to replace it with a newer model.
Problem is the f$%@ing transistor won't come off the board. I have a soldering iron and some wick, and also a de-soldering pump.
looking at the back of the board I see no solder anymore.
Any tips on removing this ?

Thanks,
Regards
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1024MAK
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Re: Trouble replacing TR4 and TR5

Post by 1024MAK »

Cut the transistor off it’s legs, then heat up the pad/joint with your iron. Make sure the iron tip is clean, then ‘tin’ it. Apply some new solder to the joint if there is not much solder left. Then VERY GENTLY, pull the leg out with fine pointed long nose pliers.

DO NOT use any force. The leg should come out as if you are pulling out of hot butter. If you use force, you will rip the plated through hole out along with the PCB pad.

When hot, solder turns to a liquid.

Then after all three legs have been removed, use a solder sucker/ solder pump or desolder braid/wick to remove the remaining solder. Again, you need the iron to heat up the pad and the solder. It may be easier if the board is held vertically so that you can heat up the pad on one side and use the solder sucker/ solder pump on the other side.

Also, press the tip of the solder sucker/ solder pump onto the joint/pad so that not much air can get in.

Mark
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popeymon
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Joined: Fri Aug 27, 2021 1:24 pm

Re: Trouble replacing TR4 and TR5

Post by popeymon »

I second Mark's advice.

I would add though that patience and practise is key.

Patience now will lead to you learning how to do it reliably, and avoid damaging your board.

Damaging a transistor is not so bad - you can buy replacements. But damaging a solder pad or the board itself, is more serious and needs a lot more work to fix or workaround.

If your solder pump is not doing the business, invest in a better one. A hot air gun can also be useful and not as expensive as a desoldering pump.

A decent magnifying glass can also be useful.

Good luck and let us know how it goes!
daniel_dlds
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Joined: Tue Dec 10, 2019 12:17 am
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Re: Trouble replacing TR4 and TR5

Post by daniel_dlds »

Hi,

Thank you for your advice and directions.
I cut the transistors off the board, and then used the solering iron to remove the rest of the wires and the solder.
Then I soldered the new transistors on the board, and now the computer is working.
Thanks
popeymon
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Re: Trouble replacing TR4 and TR5

Post by popeymon »

Excellent! :D
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