Macintosh Plus
| |
| Manufacturer | Apple Computer, Inc. |
| Type | Personal Computer |
| Release Date | January 16, 1986 |
| Discontinued | October 15, 1990 |
| Introductory Price | US$2,599 |
| CPU | Motorola 68000 @ 8 MHz |
| Memory | 1 MB RAM (expandable to 4 MB) |
| Storage | 800 KB 3.5" floppy drive, External SCSI |
| Display | 9" monochrome CRT (512×342 pixels) |
| Sound | Monaural 8-bit, 22 kHz (4-voice) |
| Dimensions | 13.6" H × 9.6" W × 10.9" D |
| Weight | 16.5 lbs (7.5 kg) |
| OS | System 3.0 – System 7.5.5 |
| Predecessor | Macintosh 512K |
| Successor | Macintosh SE |
| Codename | Mr. T |
| Model | M0001A |
Historical Background
The Macintosh Plus was the third model in Apple’s Macintosh line of personal computers, introduced on January 16, 1986. It was a significant improvement over its predecessor, the Macintosh 512K, shipping with 1 MB of RAM (expandable to 4 MB) and introducing an external SCSI port for the first time on a Mac. Priced at US$2,599 at launch, the Macintosh Plus was highly successful and remained on the market until October 1990. Originally released in beige (Pantone 453), the case color was changed to platinum gray in 1987. The Macintosh Plus was the earliest Mac capable of running System 7 (up to version 7.5.5) and introduced user-upgradable SIMM memory modules and an 800 KB double-sided floppy drive.
General Maintenance
To keep your Macintosh Plus in good condition:
- Regularly clean dust from inside the unit. This compact Mac does not have an internal fan so it essential to clean the dust from the analog and logic boards regularly.
- Inspect and replace the PRAM battery if needed. As with all Mac batteries, they have a tendancy to fail catastropically.
- Check connections regularly for corrosion or looseness.
- Periodically power on the device to maintain capacitors.
PCB Schematics
The Macintosh Plus features two main PCBs: the Logic Board and Analog Board. Detailed schematics are available in the two images attached as well as the maintenance manual. File:Macintosh Plus.pdf
Capacitor Replacement Guide
Electrolytic capacitors on the analog board commonly fail and should be replaced proactively. Recommended capacitors include:
Analog Board
- Main filter capacitor (RIFA) (4700µF 270v)
- High-voltage CRT capacitors (e.g., 10µF 160V)
- Medium-value capacitors (22µF, 33µF, 47µF)
Logic Board
There are 6 capacitors in total on the logic board, these are axial capacitors (they are becoming difficult to find now, but are still avaliable from most component suppliers such as Mouser & RS)
- 5x 33µF 16v
- 1x 1µF 50v
Retrobrite
To address plastic yellowing:
- Apply hydrogen peroxide-based Retrobrite evenly.
- Expose treated parts to UV light.
- Rinse thoroughly after treatment.
Troubleshooting
Common issues include:
No Power
- Check fuse and RIFA capacitors on the analog board.
- Inspect solder joints on analog board.
- Check the voltages on the cable connecting the analog board to the logic board.
If you still don't have power, a full recap may be required.
Chime but No Video
- Adjust brightness control.
- Check video connector and solder joints.
Unstable Operation
- Verify and adjust the +5V supply.
- Inspect and recap analog board.
Sad Mac Errors
Common Sad Mac error codes:
- 01xxxx – ROM issues.
- 02xxxx – RAM issues.
Floppy Drive Problems
- Clean and lubricate drive mechanics.
- Check and replace eject gear if necessary.