When the pit/timing PC doesn't show the passings this can have many causes but there are a few you can easily check to see where the problem is.
1. Are the passings registering in the decoder?
Most decoders will give some kind of verification when a transponder crosses the loop, either on the screen, by a small light or by a noise. As example i'll use the Tranx Decoder who shows it on it's screen
On the TranX decoder the loop is signaled by the square on arrow e, in it's normal state this square is empty. (as shown on the left picture)
To see if the decoder is receiving the passings look at this screen when a kart is passing the loop, the square on field e should become fully black (as shown on the right picture) If this doesn't happen then you know that the problem is probably between the loop and the decoder.
To solve this shut down the decoder and loop (if powered), disconnect them and reconnect them to make sure that the connection is good and power them up again. After this is done check the screen again on a passing to see if a passing is detected. If there still is no passing detected see if perhaps the problem lies with the transponder, try a different kart or try to pass a transponder separately over the loop to assure that it isn't a problem of a single transponder. If this still didn't provide a solution then the loop will probably not be connected correctly or is damaged
2. Are the Fast Reader and Fast Bridge running?
These 2 console applications are usually run on the Timing PC although sometimes they also run on the server. The Fast Reader is responsible for receiving the passings from the decoder while the Fast Bridge makes sure that these passings end up in our software. Check on the Timing PC if these are running.
3. Is the Fast Reader returning heartbeats?
To see if the connection between the Fast Reader and the decoder is okay type << verbose >> in the fast reader console app. Now you will get a confirmation that the verbose mode of the application is turned on by the message << VERBOSE -> ON >>. Most of the main brand decoders give back a heartbeat to the Fast Reader to assure that there is a connection with the decoder. If you have one of these decoders and you don't see a heartbeat appear every now and then (as shown in the picture above) there will be a problem with the connection between the decoder and the pc.
To try to solve this it's best to shut down the decoder and detach the cables and reattach them. If it is connected to the network make sure to also check if the other side of the cable is still properly connected to the network, if it's a serial cable also detach it from the pc and reattach it. Then you best restart the Fast Reader by typing << quit >> in the application and then starting it up again