Hi.
One of my car's keys (2014 skoda octavia 3) has stopped working some months ago, Don't know what happened exactly, but the lock/unlock didn't work anymore, led wouldn't blink, obviously a fresh battery didn't work.
However the key can still turn on the ignition, the car doesn't complain, so the transponder is fine, it's just an issue with the unlock mechanism.
So i opened (destroyed**) the enclosure to see if the issue was something i could fix easily like a cold joint, or a broken button / trace, i have repaired many keys with similar issues and in fact something was off.
The crystal was exposed! Che cap was somewhere around the remains of the enclosure. A broken crystal could very well be the problem.
So now i have to identify the crystal. What i've gathered so far:
First, it's a crystal and not a mems and that's obvious from the circuit/pinout (no power, only two opposite terminals are soldered to something.
Second, it's package its 3.2x2.5mm
Third, The top had "3M" printed over it
Fourth, my key carrier frequency should be 434 MHz
What could be the frequency? 3MHz? 433 MHz? I'm going to look at datasheets, hoping for the best
** This bastard enclosure is not really made to be opened, so in the end i applied a bit of brute force but in the process i damaged a capacitor. It's between a pin of the silicon and battery V-, i suspect it's some sort of VCAP (internal regulator bypass) and its value should not be critical, i'll put 100n and see how it goes, or remove it altogether, put battery, look at the signal and replace again. Worst case i can only use the key manually, as i was doing before, i have already ordered a replacement enclosure anyway