key fob not working batteries replaced where is the receiving unit

Hey guys, new to the site,
I searched for key fob but i dont think the 3 letter words are enough.
I am the original owner of 2000 v6 galant.
I have the original key fobs, i cant remember when they stopped working, but i've replaced the batteries.
No luck, the fobs dont open the doors. thats the only function. maybe a panic but the fob i have right now is only unlock and lock.
my question is how do troubleshoot this?
where is the receiving unit?
is there a certain fuse to check?

aftermarket entry systems are affordable but i just hate to find out its an easy fix and waste money on the new system.

i also have cleaned the fobs fyi, with alcohol and fixed many other fobs this way... but this did not fix mine.

and oh my googling comes up with never ending battery replacements... its annoying.

Any help is appreciated, thanks in advanced.