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Apple Macintosh Color Display General Maintenance

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Macintosh Color Display (Ben Boldt, Wikimedia Commons, public domain)

Opening, the fuse and Apple's adjustment procedures for the Macintosh Color Display (M1212), from Apple's Service Source.[1] Apple prints no anode voltage for this display. Treat the tube as charged, read CRT Discharge Procedure, and do not wear a grounding wrist strap until the CRT has been discharged.[2]

Opening

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Lay the display face down on a protective pad and swivel the base to reach the two case screws. Remove them, stand the display upright, press down on the top of the rear cover to release its two tabs from the bezel, and lift the cover off.[3]

Fuse

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The power-line fuse is on the main board. After discharging the CRT, prise one end up with a small long-stemmed screwdriver and lift it out.[2] Apple's service part is 922-0004; the Service Source gives no rating, so match the marking on the old fuse.[4]

Adjustments

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Use a short hex-head plastic tool; a long one flexes too much, and metal tools are a shock hazard. Test patterns come from Apple's Display Service Utility.[5]

Geometry and focus

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Geometry and focus (Service Source, Adjustments pp. 3-8)
Adjustment Pattern Target
Vertical centre All-White Screen Raster centred top to bottom
Horizontal centre All-White Screen Raster centred side to side
Vertical size All-White Screen 7 in ± 1/8 in (176 mm ± 2 mm) high
Horizontal size All-White Screen 9 1/4 in ± 1/8 in (235 mm ± 2 mm) wide
Focus Focus As clear as possible

Apple notes that the image width can vary by up to 3/16 inch at each side between different Macintosh models because of their video timing; set the width with the size control.[5]

Cutoff and white balance

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Do the cutoff adjustment first, with the display warmed up for at least 10 minutes, and repeat it whenever the CRT assembly or main board is replaced.[6]

  1. Display Gray Bars. Contrast to maximum, brightness to its centre detent.
  2. Turn the red, green and blue background controls fully anticlockwise.
  3. Set the green and blue drive controls to three quarters (fully clockwise, then back a quarter turn) and sub-contrast fully clockwise.
  4. Adjust G2 until the first bar is completely black and the second barely visible. Set sub-contrast back to centre.
  5. For white balance, adjust the red, green and blue background controls until the four darkest bars show no colour cast, keeping the darkest bar black. Then adjust the green and blue drive controls for no cast in the four brightest bars, and recheck the dark bars.
  6. Display the All-White Screen and set sub-contrast for 30 ± 3 foot-lamberts: 23 on the bottom scale of the R77 meter (Apple 076-0310), the middle of the 10 scale on the L-248, or 23 on the red scale of the 246.

Convergence

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With the rear cover off, display Crosshatch I. Set the convergence control on the CRT video board for the best overall convergence, then the N/S amp control for the horizontal lines at the top and bottom, the lower correction control for vertical lines at the bottom and the upper correction control for vertical lines at the top.[7]

Geometric distortion

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Use these internal controls only when the external geometry controls cannot correct the picture. On Crosshatch I, compare the top and bottom rows and the left and right sides, and adjust pin phase, vertical angle or horizontal bow as the distortion requires; if it is too bad to tell, adjust in that order, then repeat vertical angle and pin phase. If the distortion remains, the main board is at fault. The whole yoke assembly carries high voltage: do not touch it, the anode wire or the yoke wires.[8]

Yoke

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Usually needed only after a CRT replacement. Work from the rear with a mirror. Loosen the yoke clamp screw two or three turns with an insulated screwdriver, switch on, and turn the plastic yoke collar until the top and bottom of the picture are parallel with the bezel. Switch off, unplug, discharge the CRT, hold the collar and tighten the clamp screw just enough that the collar cannot slip.[9]

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References

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  1. ↑ Apple Computer, Macintosh Color Display (Service Source), 96 pp. Hosted here: File:Macintosh color display.pdf (see Macintosh Color Display Service Source). Page references are the Service Source's, with the PDF page in brackets.
  2. ↑ 2.0 2.1 Macintosh Color Display Service Source, Take Apart, Fuse, pp. 30-31 (PDF pp. 51-52).
  3. ↑ Macintosh Color Display Service Source, Take Apart, Rear Cover, pp. 1-2 (PDF pp. 22-23).
  4. ↑ Macintosh Color Display Service Source, Exploded View (PDF p. 96).
  5. ↑ 5.0 5.1 Macintosh Color Display Service Source, Adjustments, Geometry, pp. 1-8 (PDF pp. 54-61).
  6. ↑ Macintosh Color Display Service Source, Adjustments, Video, pp. 9-20 (PDF pp. 62-73).
  7. ↑ Macintosh Color Display Service Source, Adjustments, Convergence, pp. 27-29 (PDF pp. 80-82).
  8. ↑ Macintosh Color Display Service Source, Adjustments, Geometric Distortion, pp. 30-35 (PDF pp. 83-88).
  9. ↑ Macintosh Color Display Service Source, Adjustments, Yoke, pp. 36-41 (PDF pp. 89-94).


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