Upgrading and Repairing PCs

Peripheral Power Connectors

In addition to the motherboard power connectors, power supplies include a variety of peripheral power connectors for everything from floppy and hard drives to internal case fans. The following sections discuss the various types of connectors you're likely to find in your PC.

Peripheral and Floppy Drive Power Connectors

The disk drive connectors on power supplies are fairly universal with regard to pin configuration and even wire color. Figure 21.18 shows the peripheral and floppy power connectors.

Table 21.10 shows the standard disk drive power connector pinout and wire colors, whereas Table 21.11 shows the pinouts for the smaller floppy drive power connector.

Table 21.10. Peripheral Power Connector Pinout (Large Drive Power Connector)

Pin	Signal	Color	Pin	Signal	Color
1	+12V	Yellow	3	Gnd	Black
2	Gnd	Black	4	+5V	Red

Table 21.11. 3 1/2'' Floppy Power Connector Pinout (Small Drive Power Connector)

Pin	Signal	Color	Pin	Signal	Color
1	+5V	Red	3	Gnd	Black
2	Gnd	Black	4	+12V	Yellow

Note that the pin numbering and voltage designations are reversed on the two connectors. Be careful if you are making or using an adapter cable from one type of connector to another. Reversing the red and yellow wires will fry the drive or device you plug into.

To determine the location of pin 1, look at the connector carefully. It is usually embossed in the plastic connector body; however, it is often tiny and difficult to read. Fortunately, these connectors are keyed and therefore difficult to insert incorrectly. Figure 21.19 shows the keying with respect to pin numbers on the larger drive power connector.

Note Some drive connectors might supply only two wires—usually the +5V and a single ground (pins 3 and 4)—because the floppy drives in most newer systems run only on +5V and do not use the +12V at all.

Early power supplies featured only two large style drive connectors, usually called peripheral connectors today. Later power supplies featured four or more of the larger peripheral (drive) connectors, and one or two of the smaller 3 1/2'' floppy drive connectors. Depending on their power ratings and intended uses, some supplies have as many as eight peripheral/drive connectors.

If you are adding drives and need additional disk drive power connectors, Y splitter cables (see Figure 21.20) as well as large to small drive power connector adapters (see Figure 21.21) are available from many electronics supply houses (including RadioShack). These cables can adapt a single power connector to service two drives or enable you to convert the large peripheral power connector to a smaller floppy drive power connector. If you are using several Y-adapters, be sure that your total power supply output is capable of supplying the additional power.

If you want to add Serial ATA drives to an existing system, you will also need a Serial ATA–to–4-pin adapter, such as the one shown in Figure 21.22. This adapter converts a standard 4-pin power connector used by conventional hard drives to the 15-pin connector used by Serial ATA.

Physical Connector Part Numbers

The physical connectors used in industry-standard PC power supplies were originally specified by IBM for the supplies used in the original PC/XT/AT systems. They used a specific type of connector between the power supply and the motherboard (the P8 and P9 connectors) and specific connectors for the disk drives. The motherboard connectors used in all the industry-standard power supplies were unchanged from 1981 (when the IBM PC appeared) until 1995 (when Intel released the ATX standard). The original PC's four-pin disk drive connector was augmented by a smaller (also four-pin) power connector when 3 1/2'' floppy drives appeared in 1986. Table 21.12 lists the standard connectors used for motherboard and disk drive power.

Table 21.12. Physical Power Connectors

Connector Description	Female (on Power Cable)	Male (on Component)
ATX/NLX/SFX (20-pin)	Molex 39-01-2200	Molex 39-29-9202
ATX Optional (6-pin)	Molex 8993[1]	Molex 8619[2]
ATX12V Optional (4-pin)	Molex 39-01-2040	Molex 39-29-9042
PC/XT/AT/LPX P8/P9	Molex 8993[1]	Molex 8619[2]
Peripheral (large style)	AMP 1-480424-0	AMP 1-480426-0
Floppy drive (small style)	AMP 171822-4	AMP 171826-4
Serial ATA	Molex 88751[3]	Molex 87679-0001[4]

^[1] Can also use Burndy GTC6P-1.

^[2] Can also use Burndy GTC6RI.

^[3] Add -1310 or -1311 to this part number for a dual-end version, including a 4-pin connector (refer to Figure 21.22). Add -1410 or -1411 for a pigtail version.

^[4] Includes SATA data connector.

You can get these raw connectors through the electronics supply houses (Allied, Newark, and Digi-Key, for example) found in the Vendor List on the DVD. You also can get complete cable assemblies, including drive adapters that convert the large connectors into small connectors, disk drive Y splitter cables, and motherboard power extension cables, from several of the cable and miscellaneous supply houses, such as Ci Design and Key Power, as well as PC Power and Cooling.

Caution Before you install additional connectors to your power supply using Y splitters or any other type of connector, be sure your power supply is capable of delivering sufficient power for all your internal peripherals. Overloading the power supply can cause damage to electrical components and stored data.