CAUSE: The voltage on the Power/Sweep board might need
adjustment.
CURE: Use the following procedure in order to adjust the voltage
inside the Macintosh:
POWER/SWEEP ADJUSTMENT
The voltages must be verified whenever the logic board or the
power/sweep board is exchanged. If the voltages are outside of
the specified tolerances, the adjustments must be performed.
The adjustments are done with the power on, and all voltage
measurements are taken on the disk drive port with no peripheral
device attached. The internal disk drive should not be running
when the measurements are being taken.
EQUIPMENT REQUIRED: Digital Voltmeter (accurate to 0.1 volts)
Macintosh voltage test cable
Plastic alignment tool
NOTE: If you don't have the test cable, you may use wire that
has been stripped of insulation at both ends. Insert one wire
into one of the drive port pin locations indicated for ground
(Pin 1 or Pin 2 of the DB 19). Connect the other end of this wire
to the ground probe of the voltmeter. Insert the other wire into
the drive port pin location indicated for 5 or 12 volts (pin 6
for 5 volts or pin 7 for 12 volts). ALWAYS DOUBLE-CHECK THAT YOU
ARE READING THE VOLTAGES FROM THE CORRECT PINS.
CAUTION: If the banana plugs on the test cable short one another,
the Macintosh will be damaged. Make sure that the banana plugs
are insulated by their rubber hoods when not in use.
1. The power should be off, and the back cover removed. Connect
the black test lead to the ground, set the proper range on the
the voltmeter and plug the connector into the disk drive port on
the rear of the Macintosh.
2. Connect the orange test lead (12 volts) to the input on the
voltmeter. Power on the Macintosh.
The voltage reading must be between 11.90 and 12.75 volts. If
the voltage is not within these tolerances, use the alignment
tool to adjust the voltage regulator on the power/sweep board
to 11.90 to 12.75 volts. Access to voltage regulator is gained
from the noncomponent side of the power/sweep board through the
hole just above the 11 o'clock position of the speaker.
3. Power off the Macintosh. Disconnect the orange test lead and
replace its insulating hood.
4. Connect the red test lead (5 volts) to the input on the
voltmeter. Power on the Macintosh.
The voltage reading must be between 4.85 and 5.15 volts. If the
voltage is not within these tolerances, use the alignment tool to
adjust the voltage regulator (see step 2 for location of the
voltage regulator access hole) on the power/sweep board to the
specified limits.
6. Power off the Macintosh. Disconnect the red test lead and
replace its insulating hood.
7. Return and repeat steps 2 through 6 to verify that both
voltages are within the specified tolerance ranges.
IMPORTANT: If the power/sweep board cannot be adjusted so that
BOTH voltages fall within the tolerances indicated above, it
should be exchanged.