I looked into this at a job I was at recently, there are quite a few signals passing through the s5 board that are related to the group. Hall call power, fire service power, signals to the central group board, emergency power etc. However, all of these are daisy chained to all other cars in the group. Take the Eq, fire, and hall power supplies for example, if you look at the print you will see that the x-15 terminal feeds power to these circuits through the s5 board pins 19, and through a diode on the s5 board and out pin 20 to the Q12 terminal and a GS normally open contact. Since the x15 terminal in the main car is daisychained to the other cars, removing power from one car will not effect the group signals as all other cars have the exact same circuit on the s5 board that will pass power through their own x15 terminal through the s5 19, and 20 pin on to the the same group signals. Look closely there are alot of signals that go from car to car to replicate the main cars circuits to the group. That said, the only circuit that does not get daisy chained is the hall call dropping resistors. These resistors are only connected to the hall call self holding contact on the main car only, even though all the cars s5 board has the same resistors on their own board. There is no connection to the pin on the connector of the s5 board for the other cars dropping resistors. This is why when you pull the s5 board from the main car you cannot self hold the hall call relays, even though the other cars s5 boards will take over all the other circuits. I am not sure why they do this. All I can come up with is if they daisy chained the hall dropping resistors to all cars, and all cars were at the same floor and tried to cancel the same call, the current in this circuit would increase since all resistors are now in parallel, and maybe blow a fuse, or damage the hall call self holding contact. If any one has another idea, i would appreciate hearing about it. As far as adding the dropping resistors externally, they would also be in parallel with the main cars resistors thereby changing the current in the dropping circuit also if the main cars s5 resistors were left on the board. this is a very interesting situation that you have brought up vatordude, maybe someone out there knows for sure the correct answer. In the mean time, I think the board next to the s5 board, s4 is the same exact board, so if you need to pull s5 to repair it, put the s4 board in its place while you repair s5, or just swap them, and order a replacement. I think if you swap them the car will still run, but not sure at this time. let me know if you have any other ideas.
