for a functional area located in one or more modules.
In computers that use a chassis/assembly, cage/rack, or
motherboard/backplane design, the functional areas are
located on a single pcb or a group of pcb’s located in a
single area. The pcb’s generally face in one direction
whether they are used in a modular, chassis/assembly,
cage/rack, or motherboard/backplane design. Some
equipment provides card guides or brackets and locking
or tiedown bars, so pcb’s will not suffer intermittent
problems as a result of shock and vibrations.
KEYED PRINTED CIRCUIT BOARDS.—
Pcb’s are keyed to ensure that a different card type is
not inserted into a slot or the correct pcb is not inserted
backwards. The manufacturer will either cut a slot into
the plug-in side of the pcb or put plastic sleeving on one
or more of the connector pins (fig. 2-14, frame A). With
the pin/plastic sleeving method, the connector
receptacle must match the pin(s) with sleeving to
accommodate the pcb’s connector pin(s) (plug[s]) (fig.
2-14, frame B).
COLOR-CODED PRINTED CIRCUIT
BOARDS.— Pcb’s are identified by numbers. Some
pcb’s in computers show the number(s) with color
bands using the standard color code (also shown on fig.
2-14, frame B). With the color-code technique, you can
check the card number. The color code is also very
convenient when you are working with groups of cards
that have the same card number. Refer to NEETS,
Module 19, The Technician’s Handbook, for the
standard color code.
MAINTENANCE FEATURES OF PRINTED
CIRCUIT BOARDS.— Some pcb’s have indicators
and test points that are very helpful when you perform
maintenance.
Figure 2-14.—Keyed pcb’s: A. Cut slots on a pcb; B. Plastic sleeving on pins.
2-14
