Caple C871i Manual do Utilizador descarregar pdf (Página 387)

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101

Apple II Computer Info

If the reading is below 4.8V (and your Voltmeter reads accurately), you

are into 'problem' territory. Possibly, the power supply is being overloaded by

Slot cards; or, it may have developed a defect.

A different approach is to disconnect the power supply from whatever it's

powering. Connect or clip on a load-- like, say, a 20 watt 3 Ohm resistor--

from +5V to GND and measure Voltage across where the clips connect to the power

supply. (3 Ohms connected with good heavy clips will draw about 1.7 Amps.) If

the power supply is a typical Apple II power supply it should have no problem

delivering +5V into this sort of load.

Note: In general, you want to measure output as close to the power supply as

possible. Clips often introduce resistance and so measuring across the load

resistor could indicate a falsely low output.

Note: Switching power supplies should not be turned ON with no load. Something

like at least 10% of rated load should be connected across the the high-current

output (usually +5V) whatever other outputs you are checking. For an Apple II

power supply, this would be something like a 20 watt 10 Ohm resistor. For

larger switching power supplies such as used in a PC, you may need to place a

load across other outputs, too. (Usually, for a computer power supply, this

would be the +12V output.)

A really good load test needs to pull current reasonably close to the

rated output of the power supply for the Voltage leads you are checking. Like,

for a power supply rated at 4 Amps on the +5V output, you would want something

like a 1.5 Ohm load connected from the +5V output to GND.

Rubywand

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Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 387 of 572

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Caple C871i Manual do Utilizador Página 387

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