This strange key still isnt working... the LED is definitely soldered on correctly and working. I found out a number of funny "states" the key chip can be in. Changing between them is somehow done by cycling power to the PCB, while also pressing the button. Since I have no idea I just did this randomly, and by chance I found these states that the key remains in at least until the batteries are disconnected and the PCB is completely de-energized (capacitors):
Known PLIP states:
- Pressing the button does nothing (no red LED, no IR transmission, batteries are FINE and PCB is energized!!)
- Pressing the button causes red LED to light up for 1.5 seconds, no IR transmission
- Normal state - pressing the button lights up the red LED for a short time, causes an IR transmission, while the third press in a 1.5 sec interval causes a different (longer) IR transmission and the red LED to light up longer (probably this transmission is needed for the resyncing procedure)
- Pressing the button causes red LED to light up short and cause an IR transmission as in normal state (3), but subsequent key presses will not do anything unless the key is left unpressed for at least 5 seconds
When de-energizing the PCB, eg. disconnecting it from the batteries and leaving it to discharge (or discharging the capacitors forcefully), then restoring power, I usually find the key in state 2.
My other (working) key was in this state 2 for a short time with me being shocked "damn I ruined my only working key", but somehow I managed to get it back to state 3 and it worked again with the car immediately without resyncing. This happened because up to now I never *had* to do the resync for the working key - I even had the car sitting in the garden for a month without power, and after reconnecting the battery the good key worked without resyncing - so I wanted to force the good key out of sync by taking out its batteries and discharging the PCB, but still no resync was required
Contrary to that, my bad key mentioned first in this post is totally impossible to resync, in none of the mentioned states. The casing of the key has the same code inscribed as my good key, which leaves the very unlikely possibility that one of the previous owners put in a different PCB from another car, and obviously that wouldnt work.
I bought the car with the two keys, one of them being wrapped with sticky tape labeled "inoperative" - after opening the key the IR led had a broken leg. After fixing this, I arrived at the above
If the PCB in the broken key is still the original one, I tend to go with the following assumption
State 2 is a programming state, from which the key can be programmed to a car by somehow pressing the button/holding it pressed and cycling power to the PCB. Some kind of code is entered this way (perhaps the emergency code, perhaps the code inscribed in the key), either manually or by hooking the key up to some electronic equipment which does the power cycling. After this procedure, the key will go into state 3, and can be (re)synced to the car successfully.
I assume this, because I am able to get the key from state 2 to state 3 by random button presses and power cycling, however I am then unable to resync the key with my car, probably because I entered some random code via my random actions, programming the key for something not my car
So the conclusion is: I wish I knew this secret programming procedure that I'm assuming exists
I might as well go to a dealer with the key in state 2 and ask what the hell that is, maybe they see that it can be programmed again, but probably they will just say its broken, which I refuse to believe - digital electronics can either work or be broken, and this key behaves completely normal with all its in and outputs, just transmitting the wrong IR codes. I even looked at the IR transmissions by using a photodiode on a digital storage oscilloscope, comparing the transmissions with those of my working key - the 1s and 0s of the transmission were similar, and the transmission timing was identical.
Another final remark:
With the bad key in normal state, pressing the button a few times trying to lock/unlock my car and then taking the good key, I have to press the good key about 5 to 10 times until it starts locking/unlocking the car again. So the car does receive the bad key's transmissions, and somehow they make it go slightly out of sync with the good key. Strangely though, after I had the bad key hooked up to triggering electronics so it would transmit once per second, and left it this way for several hours in the car, hoping the car might somehow resync that way, after stopping the bad key's transmissions and taking the good key again, it will again work after 5 to 10 presses, even though the bad key had sent a few thousand transmissions during the hours...