Macintosh Plus Video Adjustment

Apple's drawings of the Macintosh Plus adjustment points, all reached from the rear with the cover off: the voltage regulator, the brightness control and external contrast control, the width and height controls, and the focus control.

The Macintosh Plus analog board has five adjustments: the supply voltage, the cut-off (which Apple calls brightness), the width coil, the height and the focus. Centring and tilt are set mechanically with rings and the yoke on the neck of the CRT. Apple requires the voltage to be checked after the logic board or the power/sweep board is replaced, and the video adjustments to be made whenever the CRT or the power/sweep board is replaced; after a CRT change the yoke may need adjusting too. Pina adds that a memory upgrade loads the supply and usually shrinks the picture, and that a set run for years without a fan is often well out of focus.

The same procedure applies to the Macintosh 128K, Macintosh 512K and Macintosh 512Ke, whose analog boards have the same controls; Pina's tune-up covers all of them. The Macintosh SE board has no voltage control on the analog board and is adjusted in a different order.

Symptoms

• Picture smaller than the bezel opening, or too large: width and height.
• Scan lines visible across the black border, or a grey border: cut-off.
• Soft text, or text sharp in the centre and soft in the corners: focus.
• Picture off centre, or tilted: centring rings or yoke.
• Recurring system errors, resets or a start-up loop on an upgraded machine: low +5 V.

An adjustment cannot cure a component fault. If the voltage will not reach 5.00 V, if the focus control has no effect, or if the picture blooms and buckles as brightness is raised, see Macintosh Plus Low Voltage Repair and Macintosh Plus Focus Repair. If the height or width will not adjust, or one half of the picture is missing, see Macintosh Plus Vertical Deflection Repair and Macintosh Plus Horizontal Sweep Repair.

Safety

Warning: these adjustments are made on a running machine with the cover off, with mains voltage on the analog board and the CRT at about 13 kV. Apple has the technician work from the rear of the computer and watch the screen in a mirror, and says not to reach around the computer to the controls. Work from the vinyl-jacketed side of the analog board with a plastic alignment tool, take off rings and watches, and keep one hand away from the machine. Lee recommends insulating gloves and thick-soled shoes for the centring and geometry adjustments, which bring your hand close to the yoke. See CRT Discharge Procedure before any adjustment that is made with the power off near the yoke.

Tools and parts

• A set of plastic TV alignment tools, including a hexagonal tool for the width coil. Lee whittles a soft wooden chopstick for the width coil if no tool is to hand; it must not be metal, because the core sits in a coil carrying large alternating currents.
• A multimeter. Pina specifies at least 20,000 Ω per volt; most digital meters exceed this.
• Apple's voltage test cable 077-0135, or meter probes and two insulated paper clips for the external drive port.
• A ruler, or a test pattern. Pina used his own Test Pattern Generator program with T-square, centre-cross, focusing-text and balance patterns.
• A mirror, so the screen can be watched from the rear.

Adjustment controls on the U.S. analog board (Pina, Appendix C; Apple)

Pina's name (jacket label)	Apple's name	Part	Value	Where
Voltage	Voltage regulator	R56	500 Ω trimmer	Lower right quadrant, just above the speaker
Cut-off	Brightness control	R53	2 MΩ trimmer	Upper left quadrant
Focus	Focus control	R54	2 MΩ trimmer	Upper left quadrant
Height	Height control	R55	500 kΩ trimmer	Right side, just above the voltage control
Width	Width control	L2	Tunable coil	Upper right quadrant
Brightness knob	External contrast control	R57	1 MΩ	Front of the case, under the Apple logo, left of the drive

The International board uses different designators; Pina gives R59 as its voltage control. The labels on the vinyl jacket name each control on both boards.

Procedure

Pina's order is voltage, cut-off, width, height, then a second pass to bring the three into agreement, then centring, then focus. Done out of order, each step undoes the last. Apple has the computer switched on before the video adjustments start.

Opening up

1. Switch off, unplug and remove the rear housing (battery compartment cover, any programmer's switch, five T15 screws).
2. Leave the vinyl jacket on the analog board: it insulates the solder side and carries the adjustment labels. All the adjustments are made through it.
3. Stand the machine so the jacketed side of the analog board can be reached from the rear, with a mirror placed to show the screen.

1. Supply voltage

Pina's test set-up: the red probe in socket 6 of the logic board connector, beside the blue +5 V wire, and the black probe on the chassis (Figure 3-5). Socket 2 is the empty key position.

The voltage control R56 regulates the +12 V output directly; the +5 V and −12 V outputs follow it through the transformer windings, so turning R56 moves all the rails together.

1. Clean and reseat the analog board to logic board cable first. Lee finds that tarnished contacts at J4 cause most low +5 V readings, and that raising R56 to compensate drives +12 V out of specification.
2. Measure +5 V. Pina's method: with the cord unplugged, push the red probe into socket 6 of the 11-way connector on the logic board (J7), beside the blue wire, counting sockets because socket 2 is empty; clip the black probe to the chassis. Apple's method uses test cable 077-0135 on the external drive port; see Macintosh Plus General Maintenance#Voltage check.
3. Plug in and switch on. Keep clear of the exposed joints beside the power switch.
4. Turn R56, labelled Voltage, with the plastic tool until the meter reads 5.00-5.01 V. Turn it gently; the trimmers are delicate and are not designed for repeated full turns. Lee notes that, from the jacket side, turning it clockwise lowers the voltage.
5. If 5.00 V cannot be reached, stop: the supply needs repair. Pina gives the control's range as 4.60-5.40 V.
6. Check +12 V. Apple's limits are +12 V between 11.90 and 12.75 V and +5 V between 4.85 and 5.15 V; if both cannot be brought within limits together, Apple replaces the board. Lee checks +5 V on pin 6 of the external drive connector and +12 V on pins 7 and 8, with ground on the threaded standoffs either side of it, and suggests measuring both cold and warm to catch drift.
7. Leave +5 V at 5.00 V. Pina warns against setting it higher: a cold machine draws less current, and a supply set high when warm can rise to the crowbar level at the next cold start, so the machine only "flups".

Pina also grades the supply by turning R56 up until the crowbar trips (5.35-5.40 V on a good supply, with a bong and a "flup, flup, flup" noise), then backing off at once to 5.00 V. His Table 3-1 rates a supply that reaches 5.30-5.40 V as fit for any upgrade, 5.20-5.29 V as fit for moderate memory upgrades, 5.10-5.19 V for light loads only and 5.00-5.09 V as usable but not to be loaded; one that stays below 5.00 V needs repair. He warns that the overvoltage must not be allowed to continue.

2. Cut-off

1. Turn the front brightness knob fully up.
2. Turn the cut-off control (R53, upper left quadrant) fully up. Scan lines appear and the black borders turn grey.
3. Turn the cut-off down until the scan lines just disappear and the borders are black, with no hint of grey. Apple's version of the same step: external contrast fully clockwise, the board brightness control fully anticlockwise so that white lines are visible, then clockwise until the lines just disappear, then the external control back ⅛ turn anticlockwise.
4. Set the front knob for comfortable viewing.

3. Width

1. Fit the hexagonal plastic tool into the slug of the width coil L2 (upper right quadrant) and check that the slug turns; the coil form is clear, so you can watch it over the top of the board.
2. If the slug is stuck, switch off and unplug the cord first. Pina then frees it with a metal hex key of the right size, turning it gently all the way in and all the way out to recut the thread, and returns it to the middle of its travel. Do not use a metal tool on L2 with the power on.
3. With the power on, set the width. Width increases as the core is withdrawn from the winding. Apple's target is 7 in (177.8 mm); Pina and Lee use 7.11 in, which gives 72 pixels per inch across the 512-pixel screen.

4. Height

1. Turn the height control (R55, just above the voltage control) until the picture is 4.7 in (119.4 mm) high, Apple's target, or 4.75 in, Pina's and Lee's.
2. Lee's alternative when no ruler is to hand: set the height to 4.75 in, then set the width until diagonal rows of dots cross at right angles.

5. Second pass

1. Recheck the voltage. Restoring full height and width loads the supply and often pulls +5 V down; reset it to 5.00 V.
2. Recheck height and width, which grow again when the voltage is raised. Repeat until voltage, width and height are all on target; usually one more pass is enough.

6. Centring and tilt

Apple's drawing of the centering rings on the yoke at the neck of the CRT.

1. Check centring against a centre cross or by measuring the borders. Pina leaves a small error alone: getting the picture perfectly centred is hard.
2. Centre the picture with the two rings on the neck of the CRT behind the yoke. Apple's method: hold the front ring steady and move the rear ring, then hold the rear ring steady and move the front ring. If glue holds them, Apple cuts it with an art knife. If the factory paint seal has not been broken, Pina cracks it with the power off and the cord out, wearing goggles, pushing the tabs gently in opposite directions; the neck of the tube is fragile.
3. Move the rings with one hand only, with the power on. Pina zigzags the picture into the centre in a few seconds; Lee uses the handle of an old plastic toothbrush to keep his hand well away from the yoke.

The yoke collar and yoke clamp screw, used to correct tilt (Apple).

1. If the picture is tilted, switch off and unplug, cut any glue holding the yoke collar, and loosen the yoke clamp screw two or three turns.
2. Switch on and, with one hand on the plastic spokes of the yoke collar, rotate it until the top and bottom edges of the picture are parallel with the bezel. Lee prefers to rotate the yoke only with the power off and the cord out, switching on between attempts to check.
3. Switch off, unplug and discharge the CRT. Hold the collar and tighten the clamp screw just enough that the collar cannot slip. Do not overtighten it: Lee warns that this can crack the neck of the CRT.
4. If an edge of the picture is bowed, the small magnets round the yoke set the geometry. Lee marks their starting positions, rotates them to break them free of their glue and correct the shape, then fixes them with a dab of hot glue. Distortion too large for the magnets to correct points to a fault in the yoke or flyback.

7. Focus

1. Fill the screen with small text.
2. Apple's method: turn the focus control clockwise to its limit, then back ⅛ turn anticlockwise.
3. Pina's and Lee's method: turn the control slowly through its range. At one point the corners are sharp and the centre soft, at another the reverse; settle between them. Lee sets focus with the brightness low, for the smallest dots, then checks it at normal brightness.
4. If turning the control has no effect at all, or focus is lost as the brightness is turned up, the fault is in the focus circuit; see Macintosh Plus Focus Repair.

Finishing

1. Switch off, unplug and refit the rear housing.

Testing

• The full-screen picture should measure 7.11 × 4.75 in by Pina's figures (7 × 4.7 in by Apple's), the circles of a test pattern should be round and the squares of a grid should be the same size on the left as on the right.
• With the front knob turned fully up the picture may bloom slightly, but it should not buckle; Pina reads buckling and blooming as signs of weak components.
• Lee checks that the size does not change much as brightness is raised; if it grows noticeably, he suspects poor high-voltage regulation.
• Recheck +5 V after the machine has run for a while.

Related pages

• Macintosh Plus
• Macintosh 128K, Macintosh 512K and Macintosh 512Ke
• Macintosh Plus General Maintenance
• Macintosh Plus Troubleshooting
• Macintosh Plus Low Voltage Repair
• Macintosh Plus Focus Repair
• Macintosh Plus Horizontal Sweep Repair
• Macintosh Plus Service Source
• CRT Discharge Procedure