On Gottlieb games, they absolutely serve a very important purpose known as pulse-stretching. In other words, the point relay and EOS switch on the score unit work together to ensure that very brief PF switch closures from ball hits will persist long enough to positively advance the score. Here's how it works:

- A ball hit on a PF switch energizes a point relay for a score unit.
- The point relay pulls in and locks itself on electrically through its own lockin switch.
- A different switch on the point relay energizes the drive coil for the score unit.
- The score unit drive plunger pulls in to mechanically advance the score.
- When the plunger has pulled in far enough to advance the reel, the EOS switch on the score unit opens.
- When the EOS switch opens, it cuts power to the lockin circuit of the point relay, which drops open.

Most score unit EOS failures on GTB EMs are failures where the EOS switch is always open. This is nearly always due to one of the blades of the EOS switch fracturing and breaking off from the constant hammering of the score unit as it steps. In this failure mode, you won't really notice that anything is wrong. The game will still seem to work OK, but the pulse-stretching function of the point relay will no longer be working because the lockin circuit is always open. So, the reliability of the scoring will suffer, but otherwise the game will act normally.

The other failure mode is where the EOS switch never opens. This is a very serious issue that can cause coils to fry. The most common way this happens is a failure of the switch on the point relay that energizes the score unit drive coil. Usually the switch is dirty and out of adjustment. In this failure mode, the point relay will lockin, but since the drive coil of the score unit doesn't get any power, it never indexes and the EOS switch never opens. The reason this is a serious problem is because the point relay also has yet another switch that energizes the bell or chime coil for that point score. With the point relay permanently locked on, that coil will usually fry in just a few minutes.

- TimMe