Macintosh Portable Troubleshooting

Fault-finding on both Macintosh Portable models, the original M5120 and the backlit M5126, starts from Apple's symptom charts in the Service Source, which work at module level. Restorers have since added component-level findings, given below with each symptom. Apple's rule for the charts: try the cures in order, test after each, and put the original module back before moving to the next cure.

Macintosh Portable (Hannes Grobe, Wikimedia Commons, CC BY 3.0)

Before you start

• Fit a charged main battery or a proper substitute. The Portable does not work properly without one, and the hard disk will not spin up without it. See Macintosh Portable Battery Replacement.
• Use an adapter to Apple's specification, 7.5 V nominal. David Cook warns that a higher-current PowerBook adapter fits the socket and can kill the Portable. Apple's adapter test: 7.53-7.54 V between the inside (positive) and outside of the plug on the 10 V DC range.
• On a bench supply, feed both +V pins of J17 together (6.3 V, 1 A limit is David Cook's setting). Powering only pin 3 leaves the hybrid module unregulated and can kill a line of chips.
• Recap the board and clean off all leakage before powering it for long; see Macintosh Portable Capacitor Replacement Guide.
• The power manager holds the machine's state. Apple's first step for many faults is to reset it by pressing the reset and interrupt switches at the same time.

Power

Symptom	Probable cause	Action
Blank screen, no response	Flat battery; power manager hung; keyboard or its cable; logic board	Apple's order: remove the shipping sheet between battery and contacts on a new machine; reset the power manager; connect the adapter and restart after three or four minutes; replace the main battery; check the keyboard connections, keyboard and keyboard cable; then the logic board
No response to a key press, constant current draw on a bench supply	Dead power manager (PMGR)	David Cook measured 33 mA that did not change on a key press on a board with a dead PMGR, against about 10 mA asleep and 300 mA or more awake on a good one. Check that the reset and interrupt switches read under 5 Ω pressed and over 10 kΩ released. He later revived a board by transplanting the PMGR from a PowerBook 100, which uses the same part
Control Panel settings change after the main battery is removed	Cover not refitted, or backup battery flat	Restore the settings; replace the 9 V backup battery
Adapter connected, battery desk accessory does not show the charger	Connection, battery, adapter, logic board	Check the charger connection; then the battery, the adapter and the logic board
Low-power warning soon after starting	Discharged battery or heavy drain	Connect the adapter; reduce use of the floppy and hard drives, modem and speaker
Battery does not hold its charge even when not in use	Old system software; battery; keyboard; harness; logic board	Use System 6.0.5 or later; then replace the battery, keyboard, wire harness and logic board in that order
"No reserve battery power" at startup, battery shown at 0 %	Corroded via or track in the power circuit	One M5126 had a via eaten away under a resistor array and over 6 V with heavy ripple on the 5 V rail; repairing the via fixed it
Restarts by itself after every shut-down	Leakage residue on the board	One owner cured it by scrubbing two dirty areas with a toothbrush and 99 % isopropyl alcohol
Sleeps after 15 minutes on AC with sleep disabled	The ROM ignores "don't sleep" unless it detects the charger; a battery eliminator hides the charger	Expected with a battery eliminator; see Macintosh Portable Battery Replacement

Startup

Apple's startup flowcharts:

1. Reset the power manager and switch on with no startup disk, by pressing any key except Caps Lock.
2. No startup tone and no video: keyboard, keyboard cable, then logic board. Video but no tone: speaker, then logic board. An abnormal tone: logic board.
3. No grey pattern: check the display cable, then the display, the display cable and the logic board.
4. No disk icon with a question mark: logic board. Then insert a System Tools disk; if the desktop does not appear and the drive makes no sound, keyboard, keyboard cable, logic board; if it does, a known-good disk, the drive and its cable.
5. Finally check the trackball and button.

Apple's chart for error chords at startup is a single line: replace the logic board. Restorers go further:

• A failed SWIM floppy controller can stop the machine at a grey screen with a cursor but no happy Mac or flashing disk. A SWIM can also fail actively: on one board it held data line D4 low, so the CPU read a wrong reset vector, took a bus error and restarted in a loop. Lifting D4 on the SWIM gave a chime, and a SWIM from a dead PowerBook 170 completed the repair. The Portable will not boot with the SWIM removed.
• Androda suggests that when the hybrid (M5120) or regulation circuit (M5126) fails, the 5 V rail can see the adapter's 7.5 V, which may be what kills SWIM chips.
• Sad Mac codes after the chime on an M5120 can come from sound power-up putting noise on the 5 V rail. David Cook and techknight both bypass the sound circuit's high-side load-switch MOSFET with a bodge wire so that sound power stays on, as Apple did on the backlit board.
• On a backlit board that will not chime, check that nobody has bridged the factory cut trace by the 74AC00 next to the A23 bodge wire; see Macintosh Portable (backlit).

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

Test points

The RAM, ROM and PDS slots bring out signals that can be watched with an oscilloscope or logic analyser. David Cook's guide: SYS_PWR* low means the machine is awake; SYS_RST* held low means it is halted or restarting; ROM_CS* low means the ROM is being read; BERR* low means a bus error. A healthy start reads the first eight bytes of ROM (stack pointer and reset vector) and then jumps to $0090002A. The ROM and RAM slots are numbered bottom to top on the board but top to bottom on the schematic.

Video

Symptom	Probable cause	Action
Some pixels never come on	Display	Up to five such voids is acceptable; replace the display at six or more
A pixel is always black	Display	Replace the display
A row of pixels always black, or never black	Display, display cable, logic board	Replace in that order
Display blurred, too dark or too light	Viewing angle, light, contrast setting	Adjust the angle and the contrast in the Control Panel; on the non-backlit model move it nearer the light; then the display and logic board
Backlight will not adjust or does not light (M5126)	Control panel version, inverter, display	Use Portable CDEV 1.3; check the inverter connections; replace the inverter board, the display, the logic board
Blank display, machine otherwise working	Display cable, display	Check the cable connection; replace the display, the cable, the logic board
Screen suddenly goes blank	Screen saving	Press any key except Caps Lock

The rear video port is not VGA. Do not plug a VGA cable straight into it; use a Portable video adapter.

Floppy and hard disk

Symptom	Probable cause	Action
Internal floppy drive does not work	Disk, drive, cable, logic board	Replace in that order
Disk ejects at boot, blinking X	System disk, drive, cable, logic board	Known-good system disk first
Disk will not eject	Stuck mechanism	Shut down, hold the trackball or mouse button and switch on; or push a straightened paper clip into the hole beside the drive
Internal hard disk does not work	External SCSI device off; cable; driver	Switch on external SCSI devices; check the cable; run HD SC Setup and reinitialise if the drive is seen; then the drive and logic board
Machine crashes waking from sleep	Disk driver too new	Do not use HD SC Setup newer than 7.3.1 on a Portable
Will not boot after an external SCSI device is connected	Device off, termination, duplicate ID	Switch the device on first; check termination and IDs. The Portable does not supply termination power

The Conner CP-3045 drive has a proprietary connector, and owners report its seals and head bumpers turning to goo. See Hard Drive Maintenance and Repair.

Keyboard, trackball, sound and modem

Symptom	Probable cause	Action
No response to any key	Power manager, keyboard connection	Reset the power manager (reset and interrupt switches together); check the keyboard connection; then the keyboard and logic board
Cursor does not move with the trackball	Power manager, cable, trackball	Reset the power manager; check the cables; replace the trackball cable, the trackball, the logic board
Cursor sticks or jumps	Dirty rollers	Clean the ball and rollers (see Macintosh Portable General Maintenance)
Speaker silent	Volume setting, speaker, connection	Set the volume to 1 or above; check the speaker connection; replace the speaker, the logic board One restored board had a corroded via above the positive pad of C9 that broke the left channel to the speaker
Pop or tick every 10 seconds	Apple's sound-power code writing to the power manager	Install David Cook's Quiet Portable extension
Crash when a sound plays (M5120)	Noise on the 5 V rail from the sound power switch, or dirt on the board	Bodge wire to keep sound power on, as above. One board was cured instead by ultrasonic cleaning and cleaning out the hybrid module's solder holes
Garbage on the serial ports	Old software	Use Portable INIT 1.0 and System 6.0.5 or later
Internal modem missing from the Portable control panel	Card seating	Reseat the modem card; replace it; replace the logic board

Related pages

• Macintosh Portable
• Macintosh Portable (backlit)
• Macintosh Portable General Maintenance
• Macintosh Portable Capacitor Replacement Guide
• Macintosh Portable Battery Replacement
• Macintosh Portable Service Source