Reflow with hot air gun or kitchen oven?

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I have a Toyota key fob that seems to have a dry joint or similar. It only works if I twist the PCB slightly.

Since these things cost hundreds to replace, is there any mileage in attacking it with a hot-air gun? I am reluctant to try putting it in the oven, as there are components on both sides.

 

Four legs good, two legs bad, three legs stable.

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John_A_Brown wrote:
Since these things cost hundreds to replace, ...
May be less.

https://www.autozone.com/electrical-and-lighting/remote-keyless-entry?filters=4294945239 (brand is 'Remotes Unlimited')

first page has two Toyota keyfobs at max of 100USD (didn't search the many other pages)

At the local automobile parts store, am able to acquire the complete, precise, and correct keyfob case for much less (iow, keyfob minus the PCBA)

John_A_Brown wrote:
... is there any mileage in attacking it with a hot-air gun?
No as most automotive parts are SMT packages with leads (so, soldering iron)

If there's QFN then a hardware store hot air gun though some QFN can be contact soldered.

Once the PCBA is removed from the keyfob case then can inspect the PCBA (cold solder joints, cracked traces, dirty, flux, etc)

 

"Dare to be naïve." - Buckminster Fuller

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I've found with a couple of fobs over the years that the battery and/or terminals can get dry joints or break.

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You probably don't want to eat anything that has been cooked in the same oven as SMT soldered parts.  Once or twice might be okay.  But there's very good reasons why people who use toaster ovens to reflow SMT parts make it darn clean that those ovens are NOT FOR FOOD anymore.

 

More helpfully, if you're going to have a go with a hot air gun, throw down lots of flux as well.  Flux is your friend.

 

I've had some success with hot air guns and reflowing parts.  You might consider wrapping aluminum foil around the rest of the board so you only heat the relevant joints.

 

S.

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gchapman wrote:

John_A_Brown wrote:
Since these things cost hundreds to replace, ...
May be less.

https://www.autozone.com/electrical-and-lighting/remote-keyless-entry?filters=4294945239 (brand is 'Remotes Unlimited')

first page has two Toyota keyfobs at max of 100USD (didn't search the many other pages)

At the local automobile parts store, am able to acquire the complete, precise, and correct keyfob case for much less (iow, keyfob minus the PCBA)

John_A_Brown wrote:
... is there any mileage in attacking it with a hot-air gun?
No as most automotive parts are SMT packages with leads (so, soldering iron)

If there's QFN then a hardware store hot air gun though some QFN can be contact soldered.

Once the PCBA is removed from the keyfob case then can inspect the PCBA (cold solder joints, cracked traces, dirty, flux, etc)

 

This is a keyless go thing(bloody stupid idea if you ask me, where do you put your keys when you're driving?). I'll try to find the microscope and have a better look.

 

Four legs good, two legs bad, three legs stable.

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gchapman wrote:

May be less.

In my experience it's not the keyfobs themselves that cost astronomical amounts of money it's the service charge you pay to the car maker (in my case it was Porsche) to get them reprogrammed with the correct security key to match the security system actually installed in the car. As it's the basis of the entire security system then they can charge what they like - you are a hostage to fortune.

 

If reflow prevents the need to replace and reporgram it has to be worth a go.

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Scroungre wrote:

 

More helpfully, if you're going to have a go with a hot air gun, throw down lots of flux as well.  Flux is your friend.

+1

 

Jim

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clawson wrote:

they can charge what they like

Yep. Modern day hostage taking. We were charged A$199 for my wife's Nissan Tiida a couple of years ago. A major fraction of the whole car's value. cheeky Well I might be biased.

Ross McKenzie ValuSoft Melbourne Australia

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Clean the battery contacts & rubber buttons/switches first. 

 

Also apply a soldering iron to any through hole joints 

 

If you hot gun it, bring it up "slowly" ....don't just suddenly blast it & give a big 600 degree thermal shock....but don't be too slow about it & burn up your parts.

 

Unlock your car first, in case you fail & have no spare key

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Tue. Jul 30, 2019 - 04:11 PM
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avrcandies wrote:
Unlock your car first, in case you fail & have no spare key
This has to be the winner of the "2019 Best Piece of Advice" award.

Ross McKenzie ValuSoft Melbourne Australia

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What have you got to lose?

 

You might try putting the PCB in a vise to hold it by its edges, and then gently press on components or parts of the PCB to see if you can narrow down the problem.

 

Know that I consider these devices to be rather fragile.  I recall taking one apart, many years ago, and ended up breaking more than I fixed...

 

Although my key fobs are "well sealed", with nice gaskets, etc., it always amazes me how much grime gets inside the case when I do take it apart to replace a battery.

 

JC

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Do not use the oven or the hot-air gun! They are both too hot and will float all the surface mount items on one side and make them all fall off on the other side.

 

Use a low-wattage soldering iron with flux and re-melt each and every solder joint on each side.  Feel free to use extra flux, but don't put off the procedure if you don't have any.

 

Got a scanner?  Put your keyfob PCB directly on the glass scanner surface and do a 800 dot-per-inch scan of just the area of the PCB board.  Do both sides.

Last Edited: Tue. Jul 30, 2019 - 05:18 PM
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John_A_Brown wrote:

I have a Toyota key fob that seems to have a dry joint or similar. It only works if I twist the PCB slightly.

I had the same thought for my Honda fob.  Turns out is just a poor design.  The battery doesn't sit properly.

 

I found I had to squeeze or twist the fob while pressing the button for it to work, so naturally I though dry joint.  Turns out all I needed to do was pop the battery out and put it back in.  This happens every few weeks to months.  I've tried shimming the battery with a bit of tape, in order to ensure good pressure between the battery and the contacts.  That does help, but does not fix.

 

Hopefully you trouble is similar...?

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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I ran a soldering iron over some of the doubtful looking joints, and it seems to be OK(for the time being).

Thanks for all the responses.

This is my wife's car, but I'd like my next car to be a 1953 Morris Minor, like my first car was. You could fix pretty much anything yourself, and the ignition and door locks could be opened with a nail file. We pay a high price for progress...

Four legs good, two legs bad, three legs stable.

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John_A_Brown wrote:

This is my wife's car, but I'd like my next car to be a 1953 Morris Minor, like my first car was. You could fix pretty much anything yourself, and the ignition and door locks could be opened with a nail file. We pay a high price for progress...

 

Of course, this means that anyone could open your locks and ignition with a nail file...  Beware what you wish for.  indecision  S.

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Of course, this means that anyone could open your locks and ignition with a nail file... 

I believe TSA confiscates those at the airport; you can thank them for reducing auto thefts!

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Scroungre wrote:

John_A_Brown wrote:

This is my wife's car, but I'd like my next car to be a 1953 Morris Minor, like my first car was. You could fix pretty much anything yourself, and the ignition and door locks could be opened with a nail file. We pay a high price for progress...

 

Of course, this means that anyone could open your locks and ignition with a nail file...  Beware what you wish for.  indecision  S.


Apparently it's not that hard to steal the keyless start cars of today either.

Four legs good, two legs bad, three legs stable.

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... and of course all military vehicles are keyless... or else we would have someone yelling out on the battlefield "Who's got the f'n keys?"

Ross McKenzie ValuSoft Melbourne Australia

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Related image

 

of course all military vehicles are keyless...

 

And don't confuse the Push-to-Start button with the Fire Active Targeting Weapon button!

 

JC