Macintosh Classic

Macintosh Classic

Macintosh Classic
Specifications
Manufacturer	Apple Computer, Inc.
Type	Personal computer
Released	15 October 1990
Discontinued	14 September 1992
Intro price	US$999 (floppy only) – US$1,499 (40 MB hard disk, 2 MB RAM)
CPU	Motorola 68000 @ 7.8336 MHz
Memory	1 MB soldered, expandable to 4 MB with Apple's memory expansion board
Storage	Internal 1.4 MB floppy drive; optional internal 40 MB SCSI hard disk
Display	9-inch monochrome CRT, 512 × 342 pixels
Sound	Four-voice, 8-bit D/A conversion, 22 kHz sampling
ROM	512 KB
Ports / interface	1 × ADB (mini-DIN-4); DB-19 external floppy; DB-25 SCSI; 2 × RS-422 serial (mini-DIN-8); headphone
Power	100–120 V AC, 47–63 Hz, 100 W maximum
Dimensions	13.2 in H × 9.7 in W × 11.2 in D (33.6 × 24.6 × 28.5 cm)
Weight	16–17.1 lb (7.3–7.8 kg) without a hard disk
OS / Firmware	System 6.0.7 – System 7.5.5
Predecessor	Macintosh SE
Successor	Macintosh Classic II
Codename	XO, Civic
Model no.	M0420

The Macintosh Classic, introduced on 15 October 1990, was the first Macintosh to sell for under US$1,000. It is a cost-reduced compact: the same 68000 at 7.8336 MHz as the Macintosh SE, a 1.4 MB floppy drive, an optional 40 MB hard disk, and — unlike the SE — no expansion slot and only one ADB port.

Specifications

Apple's own specification pages for this family.

Item	Specification
CPU	Motorola 68000, 7.8336 MHz, 32-bit internal data bus, 256-byte instruction and data caches
RAM	1 MB, expandable to 4 MB (120 ns or faster SIMMs)
ROM	512 KB
PRAM	256 bytes
Expansion connector	44-pin connector for the optional memory expansion board, which itself carries two SIMM connectors
Floppy	Internal 1.4 MB; optional external 800 KB or 1.4 MB
Hard disk	Optional internal 40 MB; external SCSI supported
ADB	One port, mini-DIN-4
Serial	Two RS-422 ports, mini-DIN-8
Sound	Four-voice, 8-bit D/A conversion, 22 kHz sampling. The Classic does not provide true two-channel output, although a stereo jack may be used
Video	9-inch diagonal, 512 × 342 bit-mapped monochrome
Line voltage	100–120 V AC
Frequency	47–63 Hz, single phase
Maximum power	100 W
Dimensions	13.2 × 9.7 × 11.2 in (33.6 × 24.6 × 28.5 cm)
Weight	16–17.1 lb (7.3–7.8 kg), excluding an internal hard disk

Memory

There are no SIMM sockets on the Classic's logic board. The 1 MB on board is soldered, and expansion happens on Apple's optional memory expansion board: 1 MB soldered plus a pair of 30-pin SIMM sockets and a configuration jumper, giving 2 MB, 2.5 MB or 4 MB.

Two rules from Apple that cause most of the trouble:

• the jumper must match what is fitted — "SIMMs" or "No SIMMs";
• on a 4 MB machine the modules must be eight-chip SIMMs. Apple states that 1 MB SIMMs with fewer than eight chips will not work in the Macintosh Classic.

Full procedure: Macintosh Classic Memory Upgrade Guide.

The ROM disk

The Classic is the only Macintosh that can boot from its own ROM. Holding Command-Option-X-O at startup mounts a 357 KB read-only volume named "Boot Disk" containing System 6.0.3 and Finder 6.1.x — a reference to the machine's XO codename. It is genuinely useful for diagnosis: a Classic that will not boot from a disk but does boot from ROM has a working logic board, ROM, RAM and video.

Service manual and schematics

Apple service manual

The embedded file is Apple's Macintosh Classic/Classic II/Performa 200 Service Source. Two copies are hosted here: Macintosh Classic/ Classic II/Performa 200 Service Source (115 pages) and Macintosh Classic / Classic II Service Source (113 pages, the copy embedded above). They are the same manual; the longer copy's Light Meter Setup topic covers three meter models (R77, L-248 and 246) where the shorter covers two.

Two things the manual settles for this machine: the PRAM cell is lithium and is replaced below 3.0 V, measured with the logic board out and the CRT discharged; and there is no power-supply voltage adjustment for this family - Apple's Adjustments chapter is light-meter setup, video and yoke only, so the rail-tolerance figures published for the Macintosh 128K, 512K and Plus do not apply here.

All the Apple service manuals are on the Apple Service Source page.

Logic board and analogue board

Macintosh Classic PCB images

Logic board	Analogue board
Macintosh Classic logic board File:MacintoshClassic LogicBoard Schematic.pdf	Macintosh Classic analogue board File:Classic Analog Board Schematic.pdf

Maintenance, capacitors and troubleshooting

• Macintosh Classic / Classic II General Maintenance — cleaning, the 3.6 V lithium cell and its 3.0 V replacement threshold, and what Apple does and does not publish about the rails.
• Macintosh Classic Capacitor Replacement Guide — values and positions.
• Macintosh Classic / Classic II Troubleshooting — symptom-led diagnosis.
• CRT Discharge Procedure — read before opening the case.
• Retrobrite — for the yellowed case.

Apple publishes no rail tolerance and no power-supply adjustment for this machine. Its Adjustments chapter is video and yoke work only — light meter setup, cutoff, brightness and contrast, centring, size, focus. Note also that The Dead Mac Scrolls, the standard component-level reference for the earlier compacts, explicitly does not cover the Classic.

Sad Mac codes are decoded on Sad Mac Error Codes and with the Sad Mac Decoder.

Related pages

• Macintosh SE and Macintosh SE/30
• Macintosh Classic II
• Macintosh Color Classic