Macintosh SE General Maintenance

Macintosh SE with the cover removed (Mark Baker, Wikimedia Commons, CC BY-SA 2.0)

Cleaning, the PRAM battery, connectors, known faults, rail checks and adjustments for the Macintosh SE and Macintosh SE FDHD.

The SE contains a CRT. Read CRT Discharge Procedure before opening the case. Apple's instruction is to discharge the CRT to the ground lug before disconnecting anything, because failing to do so can damage the logic board or the analogue board, and not to put on a grounding wriststrap until the CRT has been discharged.

How the SE is built

Behind the CRT the SE has three modules, where the Macintosh Plus has one power/sweep board:

• the analogue board, with the sweep and CRT drive circuits and the brightness control;
• a power supply module, held to the analogue board by four screws and connected to it by the power supply cable;
• a video board on the neck of the CRT.

Apple removes and replaces each separately. Its symptom chart for a completely dark screen with the fan not running calls for the power supply first and the analogue board second. Repair notes written for the Plus power/sweep board do not transfer to the SE.

Cleaning

• Unplug the machine and discharge the CRT before working inside.
• Remove dust from the analogue board, logic board and fan with a soft brush or compressed air.
• Clean grime and flux from boards with isopropyl alcohol (90 % or stronger) and a soft brush.
• Clean the case with a damp cloth and mild soap. For a yellowed case see Retrobrite.
• Clean the mouse rollers and ball; clean the keyboard with the keycaps off if needed.

PRAM battery

The SE's parameter memory is 256 bytes in a CMOS custom chip, kept alive by a lithium cell that Apple rated for seven years. Pina (p. 179) records two types: early boards have a 3 V half-AA cell soldered in by pigtail leads, and later boards a 3.6 V half-AA cell that snaps into a holder.

Apple's test: remove the logic board, set the meter to its 10 V DC range, and replace the cell if it reads below 2.8 V. That threshold is the SE's; the Macintosh Classic and Macintosh Classic II use 3.0 V, and other Macintosh families use other figures.

Replacing it:

• Soldered cell: cut both leads as close to the board as you can without touching the board, and solder the new cell into the extra set of holes just inside the original ones.
• Cell in a holder: pull it out.
• Either way, fit the new cell with its "+" end matching the "+" on the board.

The cell is lithium. Neutralise any leakage with a bicarbonate of soda solution, not vinegar, then rinse with isopropyl alcohol, and work with ventilation. Vinegar is for the 4.5 V alkaline battery of the Macintosh Plus and Macintosh 128K/512K. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Identifying the logic board

Two exchange boards exist. A battery in a holder means board 661-0536. A soldered battery means 661-0526; if that machine's disk controller is the SWIM (part number 344-0062), the SWIM and ROMs move to the replacement board. Pina (p. 182) names the bare boards 820-0176 (original) and 820-0250 ("DIP SIMM").

Connectors

Reseat and clean:

• the analogue board cable at J12 on the logic board (Apple's first check for clicking, chirping or thumping);
• the floppy and SCSI cables. A loose SCSI data cable after other work is one of Pina's causes of an internal disk that spins but does not mount (p. 210); a loose upper-drive cable after fitting memory or a card is another (p. 214);
• the speaker cable at J11, which Pina finds unplugged after memory, FDHD or card upgrades when there is no startup sound (p. 213);
• the CRT yoke cable and the video board on the CRT neck;
• the PDS card, if fitted.

What fails

Pina documents the SE analogue board down to the component. The main entries:

Macintosh SE analogue board faults (The Dead Mac Scrolls)

Symptom	Cause and fix	Page
Herringbone pattern across the whole display, early SE	Replace flyback T2, 157-0042A, with 157-0042C	145
Loud, display jitters, early SE	Replace crossflow fan B1 with a brushless 12 V DC fan	146
No startup sound, dark screen, hissing or sizzling	Rectifier CR2 shorted (0.00–0.01 Ω); fit an MR824	147
No startup sound, dark screen, no noise	Rectifier CR3 shorted; horizontal output transistor Q2 (BU406D) burnt; then flyback T2	148
Completely dead, no fan	On/off switch in the Sony CR44 supply	149
Startup sound, fan and disk run, screen dark, brightness has no effect	R22 (470 kΩ, ½ W) open	150
Display collapses to a line after a while; tapping the cabinet brings it back	Cracked joints: P1 pin 4 and width coil L2 (vertical line), or P1 pin 1 (horizontal line)	163–164
Poor linearity, then a vertical line and smoke	C15 (3.9 µF non-polarised) and yoke plug P1	159–161
Heavily upgraded SE goes "flup flup" and fails to start	MOSFETs Q2 and Q3 (IRF830) in the Astec supply	218

Capacitor values for the logic board, analogue board and the three power supplies are on Macintosh SE Capacitor Replacement Guide. Working on the supply means working on the primary side of a mains converter: its reservoir capacitors hold a charge after the machine is unplugged, so measure them before touching anything.

Rail checks

Apple's Guide to the Macintosh Family Hardware gives output limits for the SE and SE/30 supply:

Where to measure, and the limits

Rail	Limits	Logic board connector J12	Supply connector (to analogue board)
+5 V	4.85–5.20 V	pins 12, 13	pins 4, 9
+12 V	11.50–12.50 V (sweep); 11.50–12.80 V (disk)	pin 14	pin 10 (sweep), pin 5 (disk)
−12 V	−13.20 to −10.80 V	pin 7	pin 6
−5 V	regulated on the analogue board	pin 6	not present
Ground		pins 1–5, 8	pins 1–3, 7, 8

Ripple is specified at 20 mV (line frequency) and 40 mV (switching) peak-to-peak on +5 V, and 30 mV and 50 mV on the 12 V outputs. The SE has no voltage adjustment: Apple's Adjustments chapter covers the yoke and the video only. The R56 trimmer in Apple's Macintosh Plus procedure is the single voltage-adjust control of the 128K/512K/Plus power/sweep board, where it moves +5 V and +12 V together; the SE does not have that board. A supply outside these limits needs repair or replacement.

Adjustments

Apple's adjustments, made from the rear with a mirror, never reaching round the machine:

1. Brightness. Turn the external contrast control fully clockwise. Turn the brightness control on the analogue board anticlockwise until white lines show, then clockwise until they just disappear, then slightly anticlockwise.
2. Size. With a plastic hex tool, set the raster 7 inches wide and 4.7 inches high. Pina (p. 217) gives 7.11 × 4.75 in, with R4 labelled Height and coil L2 labelled Width.
3. Focus. Turn the focus control fully clockwise, then back one-eighth of a turn.
4. Yoke tilt. Loosen the yoke clamp two or three turns, switch on, and rotate the collar until the picture is square to the bezel. Switch off, unplug and discharge the CRT before tightening the clamp. Centre the picture with the two rings.

Pina also uses R24 (labelled Cut-off) for a display that is too bright, with visible scan lines, after a board swap (p. 167), and R27 (Focus) for poor focus after service (p. 216).

Related pages

• Macintosh SE
• Macintosh SE Capacitor Replacement Guide
• Macintosh SE Memory Upgrade Guide
• Macintosh SE Troubleshooting
• CRT Discharge Procedure
• Recommended Tools