Apple 12" Monochrome Display General Maintenance

Adjustment and care of the Macintosh 12" Monochrome Display. The targets and procedures are Apple's, from the Service Source for the display.^[1] The display was sold from 1990 to 1993, so any survivor is now over 30 years old.^[2]

Safety

The CRT holds a charge after the display is switched off and unplugged. Follow the CRT Discharge Procedure before reaching inside. Apple's own rules for its monitors include: do not work alone; remove jewellery; wear safety goggles; never wear a grounding wrist strap or work on a grounded mat while discharging the tube or making live adjustments; keep one hand in a pocket or behind your back when working on a live monitor; never touch the anode connector or anode aperture; and never lift a CRT by its neck.^[2] Apple discharges the anode to the metal part of the bezel and then leaves a clip lead from the bezel to the anode aperture, because the anode can recover some charge.^[2]

The geometry and video controls are adjusted with the display running. When adjusting from behind, watch the screen in a mirror and do not reach round the cabinet. Use a plastic screwdriver. Apple says not to attempt yoke adjustments on this display; they are set at the factory.^[1]

When to adjust

Apple calls for the geometry adjustments whenever the main board is replaced, and the video adjustment whenever the CRT or its video board is replaced; other module changes may also need the video adjustment.^[1] Test patterns come from Apple's Display Service Utility, which runs on any Macintosh with System 7.0 or later.^[3]

Geometry and focus

**Geometry and focus (Service Source, Adjustments pp. 1-8)**^[1]
Order	Control	Pattern	Target
1	H-SIZE	All-White Screen or Crosshatch II	Raster 8 7/16 in (213.5 mm) wide, ± 1/8 in (± 2 mm)
2	H-CENT	All-White Screen	Raster in the approximate centre of the screen
3	V-HEIGHT	All-White Screen	Raster 6 5/16 in (159.5 mm) high, ± 1/8 in (± 2 mm)
4	V-CENT	All-White Screen	Raster centred; recheck the height and repeat 3 and 4 if needed
5	Focus	Focus	Contrast at maximum, brightness at its detent; Focus pattern as clear as possible

Height and width affect each other, so recheck both after either is changed.^[1]

Video adjustment

Set the Monitors control panel to 16 greys. Set the contrast knob to maximum and the brightness knob to its centre detent.
Display the Gray Bars pattern. Adjust the sub-brightness control until the left bar is black and the next bar is barely distinguishable from it. If the bar edges look dashed or ragged, sub-brightness is too high: turn it down about a quarter turn and repeat.
Display the All-White Screen. With a light meter against the middle of the screen, adjust the sub-contrast control for 33 foot-lamberts ± 3.^[1]

**33 foot-lamberts on Apple's light meters**^[1]
Meter	Reading
R77 (Apple 076-0310)	25 on the bottom (10-50 fc) scale, with the 10X multiplier plate removed
L-248	Middle of the 10 scale, side switch up
246	25 on the red scale, white lens with the red dot fitted

Apple warns that the three meters read differently, that dropping a meter can spoil its accuracy, and that a doubtful meter should be checked against a known-good meter or photometer. The R77 carries a four-digit date stamp (0398 is March 1998).^[1]

Related pages

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 ^1.7 Apple Computer, Macintosh 12" Monochrome Display (Service Source), hosted as File:12 monochrome display.pdf. Adjustments: geometry and focus pp. 1-8 (PDF pp. 38-45); video pp. 9-16 (PDF pp. 46-53); light meter set-up pp. 17-22 (PDF pp. 54-59).
↑ ^2.0 ^2.1 ^2.2 Apple Computer, Macintosh Displays and Video Cards service guide, September 1996, hosted as File:Apple Macintosh Displays and Video Cards Service Guide (September 1996).pdf. CRT safety rules and discharge procedure pp. 2-3 (PDF pp. 20-21); dates introduced and discontinued, Table 2, p. 13 (PDF p. 31).
↑ Macintosh Displays and Video Cards service guide (1996), Diagnostics, Display Service Utility, p. 9 (PDF p. 27).

[ssadj-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 ^1.7 Apple Computer, Macintosh 12" Monochrome Display (Service Source), hosted as File:12 monochrome display.pdf. Adjustments: geometry and focus pp. 1-8 (PDF pp. 38-45); video pp. 9-16 (PDF pp. 46-53); light meter set-up pp. 17-22 (PDF pp. 54-59).

[sg-2] 2.0 ^2.1 ^2.2 Apple Computer, Macintosh Displays and Video Cards service guide, September 1996, hosted as File:Apple Macintosh Displays and Video Cards Service Guide (September 1996).pdf. CRT safety rules and discharge procedure pp. 2-3 (PDF pp. 20-21); dates introduced and discontinued, Table 2, p. 13 (PDF p. 31).

[sgdsu-3] Macintosh Displays and Video Cards service guide (1996), Diagnostics, Display Service Utility, p. 9 (PDF p. 27).

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