Hyundai key fob

When I bought my old(ish) Hyundai the remote lock was completely non-functional. I expected it to be nothing but synchronization issue (car and the fob can lose synchronization and thus become non-functional; if this is possible, your car's manual should describe how you can to synchronize them again) so I kept my mouth shut at that point and accepted marginally lower buying price.

Sometimes you win, and then you lose. Assholes at the shop had used pressure washer to clean the engine - something that in my opinion should never, ever be done, for any reason. Unfortunately they did and water (unsurprisingly) got in a place where it shouldn't be - block heater connector.

For those unfamiliar with these devices, a block heater is simple electric heater that is used to warm up engine (typically its cooling water, although newer aluminium engine blocks require less efficient methods) which is used at high latitudes to, well, warm the engine slightly before turning it on. When it's -30 degrees outside this will definitely make the engine wear less and start easier. So when it got cold (few months after I bought the car) I plugged it in - and shortly saw smoke coming out from the engine compartment. Connector of the heater had melted and shorted itself. D'oh. And of course dealership refused to accept any responsibility. Nothing I could do, can't prove they were guilty of reckless washing. So that cost me about 150€ to fix.

But once again I got carried away on marginally related topic, back to the key.

Like I expected, synchronization fixed the remote locking, but the range was pretty bad - few meters. That was fixed with a new key fob battery and all was good for some time again.

Until now, when it started working only occasionally. I had to press buttons multiple times to unlock (or lock) the car, and eventually lock button stopped working completely (indicated by LED no longer flashing at all when pressing it)

So, open the key fob again to see if I could find out what's wrong. Inside was this PCB (minus leads you can see at bottom.) To me it seems that the fob (and very likely its counterpart in the car) are both manufactured by Omron and Hyundai just bought them as-is, with maybe some tweaking at the car end. Not really unexpected.

On the other side are just the battery connectors. Chip was marked with Omron, and I didn't bother with the code - I expect it to be a custom chip for remote entry application, so finding any useful documentation is very unlikely anyway.

I am not exactly sure what the green gunk on the buttons is. The board was not conformally coated (which is a bit curious, now that I think of it) so that shouldn't be it. The plastic enclosure had seen some abuse so it might just be some crap that got in, but the color is off in that case.

First I tested the buttons with multimeter, no problem there. Nothing obviously wrong in the solder joints either (buttons or elsewhere), although some joints did look a bit suspicious (buttons especially; compare joints on them to, say, other components around them). It is possible that someone else had attempted repairs earlier and button joints are result of that.

Further testing was somewhat difficult without somehow powering this up, so I soldered wires to suitable places on board and started probing it oscilloscope. And what do you know, there was actual solder joint issue there - buttons worked (LED flashed) when I was probing the chip leads and pressed button.

So, at least in this case the solution was simple enough. Resolder all pin legs and fob works again. On a quick glance I couldn't see any issues at other components so I chose not to re-do all the joints. One fixed key fob - at least for now.