After having messed around a lot with my coin acceptor from adafruit, it suddenly started to reject all coins, and would no longer let them through in learning mode.
Also the click from the solenoid no longer came when a coin, that should be accepted, was put in. So I decided to take a closer look at the solenoid opening for the accepted coins.
Start by taking the two screws holding the solenoid out.
In this tube there is supposed to be a little magnet, and after a while, it gets pulled out of the tube because of the heat and pull from the solenoid.
The magnet might fall out when you take the solenoid off, but here is how it looks, and the size compared to one of the screws holding the solenoid.
Start by putting the magnet into the tube, place the solenoid on the table with the hole up, and put the tube with spring into the hole in the solenoid.
Power on the coin acceptor, and let a coin go through. If it is an accepted coin, the solenoid should pull the spring and tube in, if it pushes it away, the magnet needs to be turned opposite in the tube.
To pull the magnet back out, take an M4 (or similar) bolt and simply pull it out using the magnet itself. Turn the magnet around and try again, if it gets pulled in, make a dot with a marker so you know which end is supposed to face out.
Take the magnet back out and put a few drops of glue into the tube, then put the magnet back in with the dot facing out.
Push the magnet in so it is just below the surface of the tube like this.