Macintosh LC III

The LC III is powered by a 25MHz Motorola 68030. Apple also released the LC III+ which is essentially the same system but the board was altered to increase the clock speed to 33MHz. The LC III does not include a math co-processor but a socket is available to install a Motorola 68882.

General Information

At some point during the production run it seems that the case design was changed from the traditional LC front panel to what was used in the Macintosh LC 475.

The LC III replaces the Macintosh LC II and is the last of the Motorola 68030 based "pizza box" LCs, as the Macintosh LC 475 used the Motorola 68LC040.

Expansion

The LC III supports LC PDS expansion cards from the earlier LCs, but it also supports specific LC III PDS cards made for the larger data path of this system. The physical expansion slot is larger on the LC III to support these cards.

Notes

• Like almost all Macs of this era, you must recap the board due to old leaking capacitors.
• The LC power supplies are known to require capacitor or other repairs due to age.
• An incompatible or faulty MC68882 co-processor will cause the system to not power on.

Troubleshooting/Repair

Capacitor replacement (logic board)

The SMD capacitors on the logic board will most likely have already started leaking electrolyte out the bottom, and failing to replace them in a timely manner will result in further leakage with possible damage to nearby components. See below list of capacitors to replace:

• 5 x 47uf 16V
• 5 x 10uf 16V
• 1 x 100uf 6.3V

Capacitor replacement (power supply unit)

A dead LC PSU can typically be revived by replacing all of the aluminum capacitors and cleaning up any leakage. Any working LC power supply should also be recapped as the capacitors will likely already be leaking due to component age, and the unit will eventually fail. The LC III may use one of a few different PSU types so check the label on yours for the parts list below.

TDK

• 1 x 180uf 385v
• 2 x 270uf 25v
• 3 x 1000uf 10v
• 1 x 8.2uf 50v
• 1 x 56uf 25v
• 1 x 47uf 25v
• 1 x 270uf 10v

Dyna Comp

• 1 x 180uf 400v
• 1 x 2200uf 10v
• 2 x 1000uf 10v
• 1 x 330uf 35v
• 1 x 33uf 35v
• 1 x 10uf 35v
• 3 x 82uf 35v

ASTEC

• 1 x 180uf 400v
• 1 x 47uf 35v
• 3 x 1200uf 10v
• 1 x 470uf 16v
• 2 x 120uf 25v
• 1 x 1200uf 16v

See Also

• Apple Computer