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Apple II Computer Info

overheating reduces thermal strain on electronic parts.

Output connectors on IBM power supplies appear at first glance

to be a

bird's nest of insulated wires and connectors. But there are only three

distinct connectors:

P8: (includes blue wire -12v)

P9: (includes white wire -5v)

Molex-4: (three to five 4-pin connectors; these are for internal

drives.)

Identical colors always give the same output voltage. For example,

multiple red wires all give +5v DC. Identically-colored wires can be

soldered together to give higher amperage at the stated voltage.

Shopping for a Used IBM Power Supply: These are widely available

thrift shops, yard sales, or on the internet itself. Prices are cheap,

especially for the older larger units, because they are too large to be

used

with modern small CPUs. Prices are $20.00 or less for working power

supplies. If building your own, shop locally for a power supply so that

its operation can be verified.

When you find one, first note its odor: It should NOT have the

strong

pungent smell of cooked electronics. A mild electronic odor is o.k. ---

the

odor originates with a volatile varnish that is painted on the components.

The smell of the varnish (hopefully) signals the user that the item is

overheated. Next, plug it in and observe the cooling fan's movement. If

the

fan begins to spin quickly and maintains its speed, then the +12v line is

o.k. But if the fan fails to spin, or if it quits soon after power-up,

then

the protection circuits have intervened to shut the power supply down.

This,

by itself, is sufficient reason not to buy the power supply! Shake the

unit

and listen for rattling sounds. If the rattle is plastic, then damage is

unlikely; but if the rattle is a metal object (paper clip, pin, screw,

bolt,

etc.) then the power supply likely has suffered a short on the motherboard

and should be avoided.

Bring a DC voltmeter when shopping for a power supply. With the

115v

power on, check the DC output voltages: +12v, +5v, -12v, -5v. (NOTE: On

some power supplies, the +12v line will drop to +8v or even to total

shutoff when no load is attached to the power supply. This voltage drop

reflects the normal operation of protection/ shutdown circuits and is not

a defect. When a moderate load is attached (such as a hard drive attached

to a Molex-4 connector), then the voltage of the +12v line will return to

normal.

POWER SUPPLY CABLE: DESIGN FEATURES

HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

This power supply cable is designed for durability and top

Apple II Computer Technical Information : Apple II Family Hardware Info

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Caple C871i Manual do Utilizador Página 49

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