Car remote (key fob) repair

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Car remote (key fob) repair

Postby Fry-kun » January 11th, 2016, 2:10 pm

My car alarm key fobs haven't been working well for a long time now (years). For the past few months the max distance went down so much that I had to literally hold the fob on top of the windshield to get the car to sense it.
Of course I've changed the battery (27A) several times, tried a different fob (one had slightly longer range than another), done a visual inspection of the insides & even resoldered all the contacts to be sure they don't have microscopic cracks.

Working theory: transmit frequency had shifted over time for some reason, so the car is not picking it up anymore
I just got a new toy -- RF Explorer (via Massdrop, thanks for the discount :) -- let's check it out

Hmm, 440.7 MHz...

Oh look, there's an FCC ID! Wonder what it says, if anything.. 433.5 - 434.5 MHz, you don't say... ... m#Function 433.92 MHz

Well, no wonder the fob doesn't work so well anymore! The transmit power at 433.9 is a lot lower than at the peak

But wait, there's something adjustable here...

It's sealed with some clear plastic, let's pull that off...

And start fiddling...

A few minutes later, success -- 433.7 MHz
Fob range is now back to expected; didn't test exactly how far it goes yet, but easily works through a couple walls and from across the street.

Note: I examined 3 fobs, they all had their frequency too high. That's why I set the frequency a little lower - if it shifts up again, it'll be in the target range a bit longer.
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Joined: January 27th, 2011, 1:05 pm

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