Macintosh LC II

The LC II is powered by the Motorola 68030 at 16MHz which is an upgrade from the original Macintosh LC using the Motorola 68020. Some if not all LC II boards have an empty spot where a math co-processor socket could exist but was not installed at the factory. Network card vendors would typically include a spot for a math co-processor (Motorola 68882 most likely) on their LC PDS cards.

The LC II is replaced by the Macintosh LC III which was released in 25MHz and 33MHz variations.

General Information

Expansion

Although the Macintosh LC II computer does not include a built-in mathematics coprocessor, the V8 gate array provides the necessary decoding for an optional Motorola 68882 floating point unit (FPU). Expansion card designers can include an FPU in their card design because the FPU select signal is supplied to the PDS expansion connector.

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.

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
• 1 x 100uf 6.3V
• 10 x 10uf 16V
• 1 x 1uf 50V

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. See below for the parts list based on PSU vendor.

NOTE: these values may differ if there happens to be multiple revisions of a certain model.

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

Diagrams/Schematics

Documentation

• Macintosh LC Series/Quadra 605 Service Source
• Macintosh LC II Developer Note

See Also

• Apple Computer

External Resources

• https://cdn.preterhuman.net/texts/computing/Apple_Service_PDF/68k_Macintosh/quadra_605.lc_series.pdf - Apple Service PDF