Apple 16" Color Display General Maintenance

Parts to keep clear of during live adjustment: anode connector and wire, CRT yoke wires, flyback transformer and the base of the focus control (Apple Service Source)

Adjustment of the Macintosh 16" Color Display to Apple's figures, from the Service Source. Apple's first step for any distortion is to rule out the environment, because module swaps cannot fix it and adjusting a monitor to suit a bad location moves it away from the factory settings.

Safety

The CRT holds a charge after the display is switched off. Follow the CRT Discharge Procedure before reaching inside, and do not wear a grounding wrist strap until the CRT has been discharged. Geometry and video adjustments are made live with the rear cover off. Apple marks the anode connector and wire, the CRT yoke wires, the flyback transformer and the bottom of the focus control as parts not to touch, and uses insulated screwdrivers and its fine plastic tool 949-0386. Apple's general rules for live work: do not work alone, remove jewellery, wear safety goggles, keep one hand behind your back, and do not use a wrist strap or grounded mat.

Environment first

Metal desks, filing cabinets and shelves change the earth's field at the screen and bend the edges of the picture; fluorescent lights, other monitors and appliances make it jitter. Before adjusting, swivel or move the display, or try it in another building. If the picture changes when the display is moved, the cause is the location. A picture that has only shifted up, down or sideways may be recentred with the controls, but will need recentring again if the display is moved.

Geometry set-up

Do this before any geometry adjustment, which is usually needed after replacing the CRT or the main board.

1. Put the display on a level surface, remove the rear cover, switch on and let it warm up for 15 minutes.
2. Swivel the display to face magnetic east or west.
3. Set brightness to its detent and contrast to maximum, and display the Crosshatch pattern.

Take measurements with one eye, square on to the line from about 18 in away; straight lines look bent from the side.

Geometry, in Apple's order (Service Source, Adjustments pp. 4-13)

Step	Control	Target
1	H.SIZE	Raster 300 mm (11 7/8 in) wide, ± 3 mm
2	H.SHIFT	Raster centred horizontally in the bezel
3	KEY and KEY BAL, alternately	Left and right sides parallel to each other (KEY) and to the bezel (KEY BAL)
4	PIN AMP and PIN BAL, alternately	Left and right sides as straight as possible
5	CORNE CORR and S CORR, alternately	Sides straight into the four corners
6	H.SIZE and H.SHIFT	Recheck and repeat if needed
7	V.SIZE	Raster 225 mm (8 7/8 in) high, ± 3 mm
8	V.CENT	Raster centred vertically in the bezel
9	V.LIN	Rectangles at top and bottom the same size; recheck V.SIZE and V.CENT

Adjust a step only if it is needed to reach the target.

Focus and convergence

Display the Focus pattern and adjust FOCUS on the focus control board for the best focus over the whole screen. For convergence, display Crosshatch and use only the H.STAT control on the focus control board to bring the red, green and blue vertical lines together. Apple says not to touch the yoke controls, and notes that on a large display exact convergence at every point is not possible; aim for the best overall result.

Checking the picture

Apple says to adjust video only if the picture is unacceptable. To check it, set brightness to its detent and contrast to maximum and display Gray Bars: there should be no colour tint, and the three darkest bars should be black, barely distinguishable from black, and dark grey. On the All-White Screen the centre should read 24 foot-lamberts ± 3: 19 on the bottom scale of the R77 meter, 9 to 10 on the 2-10 scale of the L-248, or 19 on the red scale of the 246.

Cutoff and white balance

Remove the rear cover and EMI shield, warm up for 15 minutes, face the display magnetic east or west, and set brightness to its detent and contrast to maximum.

1. Display Gray Bars. Preset Sub Bright, Sub Contrast and the R, G and B Drive controls on the CRT/video board to mid-range (find the two ends of travel and set midway).
2. Turn the Red and Blue Background controls to minimum (fully clockwise). Dimming the room lights helps.
3. Adjust the Screen VR control (RV508) on the main board until the first bar is completely black. The screen should now have a green tint; if not, recheck step 1.
4. Turn the Blue Background control up (anticlockwise) slowly until the six darkest bars look blue-green, then the Red Background control until they show different shades of grey. Repeat until no bar has a tint.
5. On the All-White Screen, check for 24 foot-lamberts ± 3. If the reading is right, there is no colour in the bars and the first bar is black, stop.

Corrections after white balance (Service Source, Adjustments pp. 37-42)

Condition	Correction
No colour in the bars, too bright, first bar not black	Turn Sub Bright down slightly until the first bar is black
No colour, first bar black, too bright	Turn the R, G and B Drive controls anticlockwise in turn to reduce luminance while keeping the six brightest bars evenly grey; touch up Red and Blue Background if needed
No colour, too dim	Turn the three Drive controls clockwise in turn, then touch up the backgrounds
The six brightest bars have a tint	Adjust the R, G and B Drive controls until it goes, then reset luminance to 24 foot-lamberts with Sub Bright

After fitting a CRT/video board, check that switch SW1 is set towards the neck of the CRT before starting; otherwise the colours cannot be balanced and green is oversaturated.

Related pages

• Apple 16" Color Display
• Apple 16" Color Display Troubleshooting Guide
• Macintosh 16 Color Display Service Source
• CRT Discharge Procedure
• Recommended Tools