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25 MHz to 33 MHz Modification Upgrade for the LCIII Logic Board

The following modification was compiled from four separate forum messages describing a procedure for modifying the LCIII logic board to upgrade it from the stock 25 MHz to 33 MHz. This procedure, while relatively simple, is not indorsed or approved by Apple. If you (or whoever will do this modification) is with electronic components or using a soldering iron, do not attempt this modification.

Procedure:

1. If you're using System 7.1, download a copy of System Enabler 003 version 1.1 or higher and place it in your System folder BEFORE you perfom this modification. Failure to do so will mean your computer won't boot after you make the modification.

2. Assemble the following tools and supplies:

a. magnifying glass

b. tweezers or small pliers

c. small screwdriver

d. earthing/grounding strap

e. soldering iron, preferably one with a small, pointed tip

f. thin solder for electronic

components (available at Radio ShacK)

g. work area with good light source

3. Shut down your computer, disconnect all external cables and remove the cover

4. Remove the fan and unplug all internal cables from the logic board. The lead from the fan goes to connector M6 and the lead from the speaker goes to connector J15.

5. Pull out the two tabs on each side of the logic board and pull it an inch forward and lift it out of the case.

6. Locate resistor R14 (has "000" written on it) on the top of the logic board (located near the SIMM slots). CAREFULLY use the soldering iron to heat the solder joints at the ends of the resistor as you pull up on the resistor until it comes free of the logic board.

7. Turn the board over and locate board reference R74 which is located in approximately the same position on the back side of the board from where you just removed the resistor on the front of the board.

8. Resolder the resister to this position on the back side of the logic board. Since this is a zero Ohm resistor, you are actually just completing the circuit across this junction.

9. Reinstall the logic board, reconnect all internal cables, replace the case cover and reconnect all external cables.

10. Power up your system and make sure everything works normally. If your system won't boot, you'll have to boot from an external floppy with System 7.1 and System Enabler 003 version 1.1 or later.

GOOD LUCK!

Jeremy
"I'll see you on the Dark Side Of The Moon" - Pink Floyd

Covert Ops
68k Macs Liberated:16
I love macs, macs love me, lets go blow up some PeeCee's. With a Power surge we'll fry their Circutry.