The computer uses numerous power supplies (some visible in the photo) to provide different voltages. Relay logic activates the supplies in order, checking voltages before activating more supplies. If a voltage is bad, the power-up sequence stops. 3/10
These eight relays control the power-up sequence, closing circuits in order. The SMS card to the right checks one of the voltages. (Why relay logic? Probably because the power supplies for the transistor logic isn't energized yet. Chicken and egg.) 4/10