The display screen and lamp capsule assembly permanently connects to the basic unit. This assembly contains a legend lens, color filters, a radio frequency interference (RFI) protective screen, and four light bulbs. When the display screen and lamp capsule is pulled out, light bulbs are immediately accessible for replacement. The remaining lens, falters, and screen are accessible by sliding the lens retainer housing upward.

THUMBWHEEL SWITCHES.- Two types of rotary thumbwheel switches are used on the EP2 panel-local electronic fuze order switches and type assignment switches (refer to fig. 5-73). Each thumbwheel dial contains one layer of multiple contact points; each contact point connects to a common wiper for a given dial position. The numerical thumbwheel dials have 10 positions; the round assignment thumbwheel dials have 12 positions. No position stops exist for any of the dials. All thumbwheel switches are water and dust protected by a hinged transparent

Figure 5-73.-Thumbwheel switches.

covering (bezel assembly). The covering screws down tightly whenever dial positions are not being changed.

ROTARY SWITCH.- The rotary switch (refer to figs. 5-3 and 5-74) contains layers of multiple contacts. The layers are mounted in a circular pattern inside a cylindrical housing which has external connectors. Rotary switches have from two to seven layers of enclosed contacts and from two to six possible switch positions.

Circuit Cards

The circuit cards (fig. 5-75) contain the transistors, integrated circuits, capacitors, diodes, and other electronic components. These rectangular fiberglass

^{Figure 5-74.-Rotary switch.}

Figure 5-75.-Circuit cards.

cards, coated with a clear epoxy insulating lacquer, have printed conductors and contacts on both sides.

The top and bottom edges of the card slide in mounting channels that guide the contacts into a circuit card connector in the circuit card rack. Key pins in a locking bar on a comer of the circuit card prevent the wrong circuit card from being inserted into a connector. A cap screw on the locking bar locks the card into place.

The circuit card rack in EP2 holds four rows of circuit cards, including the microprocessor CPU circuit card and all microprocessor-associated cards. Other circuit card racks include the electronic components housing located in EP2 which holds six cards; the circuit card housing in EP1 which holds three cards; and the electrical components housing on the ventilation system duct which holds three circuit cards.

Indicating Lights

The three types of indicating lights used on the panels are indicator lights, indicator lamps, and LEDs. The indicator lights used on EP1 indicate that an electrical circuit is energized and that power is available. The indicator light has a step-down transformer in the base to reduce the supply voltages from EP1 to the 2 volts needed for the two bulbs in each indicator light.

Indicator lamps are used on EP2 as operational sequence indicators, mount-ready status indicators, and warning indicators. Indicator lamps contain from 3 to 16 lights, with each light illuminated by two 28-volt bulbs. For some older gun mounts these indicator lamps on EP2 are replaced with LEDs.

On older mounts, LEDs on EP2 are limited to the weapons control round order display. These LEDs are mounted on one circuit card assembly containing the necessary current-limiting resistors and using a +5 VDC power supply.