Apple AppleVision 850 Display General Maintenance

Exploded view of the AppleVision 850 and 850AV with part numbers (Apple Service Source)

Care and adjustment of the AppleVision 850 and AppleVision 850AV displays, renamed the 20-inch ColorSync Display and ColorSync AV Display in November 1997. The two share their main deflection board, CRT/video board and adjustment procedures. Most adjustments are made in software from a Macintosh; a few are made by hand inside the cabinet with the display running.

Safety

The CRT anode runs at 27 kV. Apple's rule whenever the housing is off and before any module is replaced: discharge the CRT and remove the anode cap, then clip a lead from the anode aperture to the braided ground strap round the CRT and leave it there, and only then put on a grounding wrist strap. See the CRT Discharge Procedure. Live adjustments are made with the housing off: do not work alone, keep one hand behind your back, and do not wear a wrist strap while the display is running.

Apple's tool list: magnetised Phillips screwdriver, a long magnetised T-15 Torx driver, a 3/32 in ball-end hex driver, jeweller's screwdrivers, needle-nose pliers, a flat-blade screwdriver and the CRT discharge tool (076-0381); a turntable, a torque wrench and a blunt plastic tool for the screw covers on the mid housing are suggested.

Cleaning

1. Switch off the computer and display and unplug the display's power cord.
2. Wipe the case with a soft cloth dampened with water. Do not use aerosol sprays, solvents or abrasives.
3. Wipe the screen with a mild, non-abrasive cleaner on a soft cloth; do not spray it on the screen. Apple warns that cleaners containing alcohol or acetone can damage the screen.

Keep the vents clear.

Software adjustments

With the AppleVision software installed and the display's ADB cable connected, geometry (size, position, rotation, pincushion), convergence and colour are set in the Monitors & Sound control panel. Apple recommends the 9300 K white point for most programs, and the control panel's Recalibrate button re-measures the colour; recalibration can take from 20 seconds to two and a half minutes. Restarting with Command-Option-A-V held down returns the display to its factory settings.

Hand adjustments

Apple allows four hand adjustments; it says not to touch any other control on the deflection yoke, because the result can be misconvergence that cannot be undone.

Hand adjustments (Service Source, Troubleshooting pp. 7, 10-11)

Control	Where	Use
H focus and V focus	The two top controls on the flyback transformer	Best centre-of-screen focus on the Display Service Utility focus pattern (percent signs)
Horizontal static convergence	Potentiometer at the lower left of the CRT/video board, plastic hex tool	Vertical lines in the centre and over most of the screen
TLH and APH	Wheels on top of the deflection yoke	Convergence of vertical lines at the left and right sides; several turns are needed to see an effect, and APH rarely needs adjusting

Adjust focus before judging convergence, since poor convergence is often mistaken for poor focus. Apple notes that convergence is never perfect over the whole screen.

High voltage

High voltage can be adjusted only with Apple's Display Service Utility; clicking its Adjust Geometry button checks the high voltage and loads a nominal value if it is out of range. To measure it:

1. Switch off the computer and display, unplug the power and video/ADB cables and wait at least two minutes.
2. Remove the blank plate (850) or microphone (850AV), top housing, rear housing, front bezel and mid housing.
3. Fit Apple's high-voltage probe (076-0392) to the meter and secure its ground lead to the chassis. Apple says other probes will not read accurately for this procedure.
4. Slide the probe under the anode cap from the rear of the CRT, reconnect the cables and switch on.
5. The meter should read 27 V DC ± 0.5 V, which is 27 kV. A reading of 0 V means the main deflection board. Switch off and unplug before removing the probe.

After a main deflection board is replaced, Apple sets 27 kV with the utility's slider while reading the probe, then adjusts focus and the H-Focus (dynamic focus) slider, first at 1152 × 870 and then at the other two Macintosh resolutions.

Saving the set-up data

The display's set-up parameters are stored on the CRT/video board. Before replacing that board, use the Display Service Utility's Create File button to save them to a file named Parameter Settings 850 (about three minutes), copy the file to a backup folder without moving or renaming the original, and after fitting the new board write it back with Write File. Then adjust geometry and convergence and recalibrate the white point. Check first that the yoke wires to BF1 and BL1 on the main deflection board are not clamped in with the ribbon cables; Apple gives that bundling as a cause of corrupted data.

Related pages

• Apple AppleVision 850 Display
• Apple AppleVision 850AV Display
• Apple AppleVision 850 Display Troubleshooting Guide
• Apple AppleVision 850 Display Capacitor Replacement Guide
• 20" ColorSync Displays Service Source
• CRT Discharge Procedure