Apple Multiple Scan 20 Display Troubleshooting Guide

Fault-finding on the Apple Multiple Scan 20 Display, built on Apple's symptom charts. Apple lists cures in order of likelihood: try the first, check whether the symptom has gone, and refit the original module before trying the next.^[1] The charts work at module level. Before opening the display, read CRT Discharge Procedure; Apple Multiple Scan 20 Display General Maintenance has the take-apart steps and the EEPROM procedure.

First checks

Apple's first checklist says that over 60 per cent of the Multiple Scan 20 modules returned for repair worked.^[1]

Check that the computer supports the display. It is not fully compatible with every Macintosh and PowerBook, and many models drive it only at 640 × 480 (see Specifications).^[1]
A CRT raster is never a perfect rectangle. Bowing and bent edges can come from magnetised metal furniture; jitter, faint lines and movement from electronic equipment and fluorescent lights. Move the display to another room or building before replacing anything.^[1]
A badly adjusted picture can look like a deflection board or CRT fault. Go through the front-panel adjustments first.^[1]
Apple says CRTs rarely fail.^[1]
Identify the version. A serial number ending in 5B4, 5J2, 5JE or 5JF is a Rev. B, which needs Rev. B main deflection, microprocessor and power supply boards.^[1]

Microprocessor board and the EEPROM

The microprocessor control board appears in most of the charts below. Its EEPROM holds the adjustment data for that particular display, so every chart that replaces it starts by saving the settings ("Display Setting Restoration"). If the data is lost before it has been written to the new board, the display cannot be repaired.^[1]

Symptom charts

**Apple's symptom charts, Multiple Scan 20**^[1]
Symptom	Cures in Apple's order	Service Source page
No raster; power light on	1. Check the video cable at the computer or video card. 2. Replace the main deflection board. 3. Replace the microprocessor board (save the EEPROM settings first).	Troubleshooting 10
Raster jumps	Replace the microprocessor board (save the settings first).	11
Colour blotches at the edges of an all-white screen	1. Degauss with an external degaussing coil. 2. Move the display and degauss again. Caused by strong magnetic fields; changing boards will not cure it.	11
Raster distorted, no picture	1. Replace the microprocessor board (save the settings first). 2. Replace the main deflection board.	12
Display does not power up	1. Check the video cable and other cable connections. 2. Replace the power supply.	13
Display shuts down	1. Check the video cable. 2. Replace the main deflection board. 3. Replace the CRT/video board.	13
Convergence light blinks or stays on (power light may blink)	Replace the microprocessor board (save the settings first).	14
Rotation light blinks or stays on	Replace the main deflection board.	15
Size light blinks or stays on	1. Replace the main deflection board. 2. Replace the CRT/video board. 3. Replace the microprocessor board (save the settings first).	16
Centring light blinks or stays on	1. Replace the main deflection board. 2. Replace the microprocessor board (save the settings first).	17
Picture dim; front-panel controls do not brighten it	1. Make sure the screen does not face a window or other bright light. 2. Replace the CRT/video board.	18
Vertical jitter	1. Move the display and see whether it persists (often electromagnetic interference from equipment, fluorescent lights or power lines). 2. Replace the main deflection board.	18
Snapping sound; raster blinks for an instant	Normal in new monitors (particles inside the CRT); a fault only if it persists after 40 hours of use. 1. Replace the power supply. 2. Look for arcing on the main deflection board and replace it if found; otherwise the CRT is defective.	19
Picture colour uneven	Adjust rotation and colour uniformity.	19
Focus blurred on one side	1. Adjust focus (Apple refers to the convergence adjustment). 2. Replace the main deflection board.	19
On first use, a cloth-like pattern of fine black, dark grey or white vertical lines	1. With an all-white pattern, adjust size and rotation to make the lines less visible without discolouring the picture. 2. At power-on, tap the side of the display lightly so the picture moves; tap again after 30 minutes' warm-up. 3. Apple's last step was a call to its service provider support line to replace the display.	20

The same charts, with the version check and EEPROM procedure, are in Apple's 1996 service guide.^[2]

Power and fuse

The fuse is on the power supply, under a plastic cover. The Service Source says to replace it with one of the same current and voltage rating; Apple's parts list gives 6.3 A, 250 V.^[1]^[2] The Rev. B takes its own supply, 661-1007, in place of 661-0508.^[2]

One owner's display clicked and then gave off smoke. The fuse had not blown; a capacitor on the power supply board had a split vent, and the owner replaced the board's electrolytics other than the 560 µF 400 V reservoir.^[3] See Capacitor Failure Symptoms.

Related pages

References

↑ ^1.00 ^1.01 ^1.02 ^1.03 ^1.04 ^1.05 ^1.06 ^1.07 ^1.08 ^1.09 Apple Computer, Apple Multiple Scan 20 Display (Service Source), 1995, hosted as File:Multiple scan 20 display.pdf (see Apple Multiple Scan 20 Service Source). PDF page numbers: Version Differences pp. 3-4; Monitor Distortion pp. 5-11; General p. 22; First Checklist pp. 23-25; Display Setting Restoration pp. 26-30; Symptom Charts: Raster pp. 31-33, Power p. 34, Indicator Lights pp. 35-38, Miscellaneous pp. 39-41; Take Apart: fuse pp. 63-64; Adjustments: geometry pp. 102-109, convergence pp. 110-112.
↑ ^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. Apple Multiple Scan 20 Display chapter: parts list p. 114 (PDF p. 132), including fuse 6.3 A 250 V, 922-0735, and the Rev. B board numbers; troubleshooting and EEPROM pp. 115-121 (PDF pp. 133-139).
↑ TinkerDifferent forum thread "Recapping the Apple Multiple Scan 20 Display! (Sad Ending)", April 2025. _nec6678: reported as clicking and then letting out smoke; fuse not blown; one capacitor on the power supply board had a split vent; replaced the power supply board capacitors except the large 400 V 560 µF capacitor; with the tube broken, the power lights flashed and the centring indicator was lit, and the display switched itself back on a few seconds after being turned off. Community repair report.

[ss20-1] 1.00 ^1.01 ^1.02 ^1.03 ^1.04 ^1.05 ^1.06 ^1.07 ^1.08 ^1.09 Apple Computer, Apple Multiple Scan 20 Display (Service Source), 1995, hosted as File:Multiple scan 20 display.pdf (see Apple Multiple Scan 20 Service Source). PDF page numbers: Version Differences pp. 3-4; Monitor Distortion pp. 5-11; General p. 22; First Checklist pp. 23-25; Display Setting Restoration pp. 26-30; Symptom Charts: Raster pp. 31-33, Power p. 34, Indicator Lights pp. 35-38, Miscellaneous pp. 39-41; Take Apart: fuse pp. 63-64; Adjustments: geometry pp. 102-109, convergence pp. 110-112.

[sgparts-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. Apple Multiple Scan 20 Display chapter: parts list p. 114 (PDF p. 132), including fuse 6.3 A 250 V, 922-0735, and the Rev. B board numbers; troubleshooting and EEPROM pp. 115-121 (PDF pp. 133-139).

[td4305-3] TinkerDifferent forum thread "Recapping the Apple Multiple Scan 20 Display! (Sad Ending)", April 2025. _nec6678: reported as clicking and then letting out smoke; fuse not blown; one capacitor on the power supply board had a split vent; replaced the power supply board capacitors except the large 400 V 560 µF capacitor; with the tube broken, the power lights flashed and the centring indicator was lit, and the display switched itself back on a few seconds after being turned off. Community repair report.

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