How to DEsolder transistor

[Welchs101]

I am having a lot of trouble desoldering the transistors shown in the picture.

I think they need replacing since there are "burn" marks around the 4 transistors. I have already replaced the bad-caps on this board and i could just try and hook everything up and see if it works but i was thinking i should go ahead and remove/replace these transistors. what doyou think?

Definitely need help to identify a way to de-solder these transistors.

[i4004]

Re: How to DEsolder transistor

decent wattage iron, first do the big contact(lifting gently that area (with something pointy underneath, or tweezers from above, etc.) while heating it), then 2 remaining small contacts shouldn't be a problem.

or you can cut the 2 small contacts first, and then do the big one.
that way you have good spot for lifting it while heating big contact.

[Welchs101]

Re: How to DEsolder transistor

Thanks! I was wondering if i should cut the small leads. But i will try not cutting them first to see if that works.

thanks.

[i4004]

Re: How to DEsolder transistor

be carefull when doing it, you don't want solder splatter in your eye if you're pulling it up too hard!

[Krankshaft]

Re: How to DEsolder transistor

There is nothing wrong with clipping the components leads with side cutters to aid in removal.

As long as you don't intend to reinstall the part.

If you don't want to clip. Place a sewing needle under the tab just make sure it stays in position don't press it in yet melt the solder now press it in. Next grab the needle and gently lift up. Just high enough to clear any solder you don't want to rip the other 2 traces.

If you clip the other 2 leads there is no need to use a needle just push it off with the iron.

I see darkening like that all the time it's just a result of transistor heat. The tab of the transistor dissipates it's heat through that trace on the PCB. The designers usually make that trace bigger to give more surface area for dissipation.

It's the price we pay due to the miniaturization of technology with heatsink space at a premium.

Did you test them with a DMM for shorts?

No need to replace them if they aren't faulty.

[stj]

Re: How to DEsolder transistor

that's poor advice,
if you lift the package first then you risk lifting the tracks under the pins.

start by cutting the pins, or put the iron on the side of a pin where it touches the board, when the solder melts you bend up the pin with a small screwdriver or something like a mutimeter probe.

once the pins are up, you put the iron on the tab of the device till the solder melts and then quickly lift it off with tweezers or longnose plyers.


personally i just use a hot-air system.

[Krankshaft]

Re: How to DEsolder transistor

I use that process on 4-8 pin SOIC packages blob one side with solder melt and lift with needle. Repeat for other side.

Never tore a trace yet.

Anyhow as I said before this is ONLY if you want to save the component. Or if you really want to make the process easy get some Chipquik. If not clip the leads.

[i4004]

Re: How to DEsolder transistor

>if you lift the package first then you risk lifting the tracks under the pins.

i doubt it...those traces are a bit tougher than that...and pins will bend.
it would need to be a willful exertion of great force(once the big contact is lifted) to actually do that...
and i don't think anybody would be doing that, unless crazy.

either way, he can pick a way he prefers.
any advice given here will work.

[stj]

Re: How to DEsolder transistor

probably worth saying for those who never lifted that type of package, that the entire package is soldered down.
the tab is just the end sticking out.

[Krankshaft]

Re: How to DEsolder transistor

I have actually removed TO252 packages (a few LCD inverters I worked on used these packages as driver transistors) I remember mentioning a few posts back something about thermal transfer. Which caused the board darkening.

The only way to make thermal contact without a fastener like a screw or thermal epoxy is with solder please read before you post.

No need to get snippy either.

[Welchs101]

Re: How to DEsolder transistor

I decided to go ahead and leave the old ones in place and try it out. I did measure the devices as best i could with a multimeter and from what i could tell the devices seemed ok. At least comparable to the "new" devices i had ordered from digikey.

I put it all back together and IT WORKED. I burned it in (since my last post here) and it all seems to work well.

Having said all this i do really appreaciate the inputs on how to remove this device. I have routinely had trouble removing such devices and i knew there had to be a better way than what i was doing. Thanks for ALL the inputs.

[Jerry Hall]

Re: How to DEsolder transistor

For the Dell/beng 2172/3fpb I clamp on a medical forcips to the heat sink and let gravity work for me. It usually results in clean holes