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.
gchapman 
Since these things cost hundreds to replace, ...
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)
... is there any mileage in attacking it with a hot-air gun?
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)
I've found with a couple of fobs over the years that the battery and/or terminals can get dry joints or break.
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.
John_A_Brown wrote:May be less.Since these things cost hundreds to replace, ...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:No as most automotive parts are SMT packages with leads (so, soldering iron)... is there any mileage in attacking it with a hot-air gun?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.
clawson 
May be less.
If reflow prevents the need to replace and reporgram it has to be worth a go.
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
valusoft 
they can charge what they like
Well I might be biased.
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
valusoft Unlock your car first, in case you fail & have no spare key
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
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.
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 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...?
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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...
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. 
S.
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!
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.
valusoft ... 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?"
of course all military vehicles are keyless...
And don't confuse the Push-to-Start button with the Fire Active Targeting Weapon button!
JC
