Apple Color High-Resolution RGB Monitor General Maintenance

Brightness and contrast knobs and the geometry controls, rear cover removed (Apple Service Source)

Care and adjustment of the AppleColor High-Resolution RGB Monitor, the 13-inch Trinitron monitor Apple sold from 1987 to 1992. The procedures and target figures are Apple's, from the Service Source and the owner's guide. Most of these monitors are now 30 or more years old.

Safety

The CRT holds a charge high enough to injure after the monitor is switched off. Follow the CRT Discharge Procedure before touching anything inside. Apple's take-apart procedures discharge the CRT before any module is removed and warn never to wear a grounding wrist strap until the CRT has been discharged. Apple's manual gives no anode voltage for this monitor.

Several adjustments below are made with the monitor running and the cover off. Apple's instructions for the convergence and distortion controls on deflection board D mark the very-high-voltage areas of the board and warn not to touch the yoke assembly, the anode wire or the yoke wires. Use plastic adjustment tools, and when working from behind, watch the screen in a mirror. Do not reach round the cabinet to the controls.

Cleaning

1. Switch the monitor off and pull its power cable from the computer (or from the wall on a Macintosh LC set-up).
2. Wipe the cabinet with a damp, lint-free cloth. Apple says not to use aerosol sprays, alcohol, solvents or abrasives.
3. Clean the screen with household glass cleaner applied to a cloth, not sprayed on the glass.

Keep the cooling vents clear. Apple recommends a screen saver that keeps a moving image on a dark screen, or turning the brightness down, to avoid burning a static image into the phosphor.

Degaussing and warm-up

The monitor degausses itself every time it is switched on. If it is left on for more than three days, press the manual degauss button below the on/off switch on the back panel; the picture flickers for a few seconds. Patches of colour that the degauss button does not clear are a power supply fault in Apple's symptom charts.

Allow about 20 minutes for the picture to settle after switch-on. For everyday use, set contrast to maximum and brightness to the detent at the centre of its travel; Apple advises keeping brightness below maximum to extend the life of the tube.

Geometry

The geometry controls can be reached through the service access panel at the rear without removing the cover. Do them in order, using Apple's Display Service Utility for the test patterns. Apple says not to attempt yoke adjustments; they are set at the factory.

Geometry targets (Service Source, Adjustments pp. 1-7)

Adjustment	Pattern	Target
Horizontal size	All-White Screen	Raster 9 1/4 in (235 mm) wide, ± 1/8 in (± 2 mm)
Vertical size (after horizontal size)	Crosshatch II	Raster 7 in (176 mm) high, ± 1/8 in (± 2 mm)
Focus	Focus	Best clarity halfway between the centre and the left and right edges

The width can vary by up to 3/16 in at each side between Macintosh models because of differences in video timing, so check horizontal size whenever the monitor is moved to a different computer.

Video: cutoff and white balance

Apple says to redo the cutoff adjustment whenever the CRT assembly, deflection board D or the video colour board is replaced, and warns that a wrong cutoff setting severely shortens the life of the picture tube. Work in a dimly lit room with the monitor warmed up for at least 10 minutes, the rear cover, EMI shield and video board shield removed.

Cutoff

1. Remove the video cable from the monitor and switch it on. Set contrast to maximum and brightness to its detent.
2. On the video colour board (B board) set B.BKG, G.BKG, R.BKG, R.DRIVE, G.DRIVE, B.DRIVE, SUB CONT and SUB BRT to mid-range. On Rev. B boards the R.BKG and B.BKG labels are swapped.
3. Set a voltmeter to measure 140 V DC and connect its black lead to the chassis.
4. With the red lead on the cathode pin marked KR on the CRT board (C board), adjust R.BKG for 140 V ± 2 V. Repeat at KG with G.BKG and at KB with B.BKG.
5. Turn the cutoff control on the H board up until the raster is just visible, then back until it just disappears. If you turn it too far the monitor may shut down: switch off, turn cutoff fully anticlockwise, wait 30 seconds and start again.

White balance

1. Switch off, reconnect the video cable and switch on. Display the Gray Bars pattern.
2. Adjust B.BKG, G.BKG and R.BKG until the three darkest bars have no tint, the leftmost bar is as black as the border, the second is barely distinguishable from it and the third is dark grey.
3. With a light meter, adjust G.DRIVE until the brightest bar reads 24 foot-lamberts ± 3 (9 to 10 on the 2-10 scale of the L-248 meter, 19 on the red scale of the 246).
4. Adjust R.DRIVE and B.DRIVE until the three brightest bars show no predominant colour, then recheck the background controls.
5. For fine tuning, set SUB CONT so the brightest bar reads 24 foot-lamberts and SUB BRT so the leftmost bar is completely black and the next barely visible.

Convergence

Apple's convergence adjustment is separate from the factory convergence magnets on the yoke, which must not be touched. Warm the monitor for 15 to 20 minutes and display Crosshatch I. If the lines are pure white, leave it alone.

1. Press the degauss switch and remove the service panel cover.
2. Turn V-STAT until the colour-shadowed horizontal lines blend into white, then H-STAT for the vertical lines.
3. If H-STAT has too little range, switch off, remove the cover, EMI shield and video board shield, and adjust H-STAT on the board directly.
4. If the lines at the top or bottom are still out, adjust V-TOP (RV518) or V-BOTTOM (RV517) on deflection board D with Apple's adjustment tool 949-0386, keeping clear of the marked high-voltage areas.

Geometric distortion

Use these controls on deflection board D only when the external geometry controls cannot correct the shape. Display Crosshatch I or II and compare the boxes at top and bottom and at left and right. The controls are PIN AMP (RV506), PIN PHASE (RV505), V. ANGLE (RV516), V. BOW (RV511) and V. LIN (RV509). If the distortion is too bad to diagnose, adjust in Apple's order: PIN AMP, PIN PHASE, V. ANGLE, V. BOW, then V. ANGLE and PIN PHASE again. If it still cannot be corrected, Apple replaces deflection board D.

Light meters

Apple's luminance figures assume one of its light meters. For the L-248, press the red button to check the battery, move the side switch down for the 2-10 scale, uncover the lens and press the read switch with the lens against the middle of the screen. For the 246, remove the metal slide, fit the white lens with the red dot and turn the lens towards the screen. Apple notes that meters drift with age and should be checked against a known-good meter or photometer.

Related pages

• Apple Color High-Resolution RGB Monitor
• Apple Color High-Resolution RGB Monitor Troubleshooting Guide
• AppleColor High-Resolution RGB Monitor Service Source
• CRT Discharge Procedure
• Recommended Tools