Apple Multiple Scan 720 Display Troubleshooting Guide
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Fault-finding on the Apple Multiple Scan 720 Display, following Apple's symptom charts. Cures are listed in order of likelihood; try one at a time and refit the original module before moving on.[1] Apple's only internal repair is the main deflection board and CRT/video board module, 661-1466; Apple Multiple Scan 720 Display General Maintenance has the take-apart steps and the B+, high-voltage, screen, centring and focus procedures. Read CRT Discharge Procedure before opening the display.
First checks
[edit | edit source]- The display works with any computer that produces a horizontal scan of 30-70 kHz and a vertical refresh of 48-160 Hz; some need a video card. It looks best in one of the factory preset modes.[1]
- Bowed or bent raster edges can come from magnetised metal furniture, and jitter, faint lines or movement from electronic equipment and fluorescent lights. Move the display to another room or building to rule these out. A raster shifted only up, down or sideways can be put right with the user controls.[1]
- A badly adjusted picture can look like a deflection board or CRT fault, and Apple says CRTs rarely fail.[1]
Power Macintosh 5500 and 6500
[edit | edit source]Apple's Hot Issues chapter puts jittery or blurred video on these computers down to the computer. Jitter, where pixels shimmer at the edges of the screen, windows or dialogs, affects 225 and 250 MHz logic boards: PM 5500 serial numbers TY705xxxxx to TY715xxxxx and PM 6500 XB708xxxxx to XB718xxxxx. Blurring over the whole screen at 832 × 624 and above affects PM 6500 XB708xxxxx to XB723xxxxx. A PM 6500 should not be set above 1152 × 870; higher settings give misaligned, skewed, dim or blurred pictures on any monitor.[1]
Symptom charts
[edit | edit source]| Symptom | Cures in Apple's order | Service Source page |
|---|---|---|
| No raster, LED on | 1. Check the power cord and video cable; tighten the thumbscrews, and secure the cable to the video card if one is used. 2. Adjust brightness and contrast. 3. A screen saver may be running: move the mouse or press a key. 4. Replace the main deflection board and CRT/video board module, then do the non-user adjustments. | Troubleshooting 4 |
| No raster, LED off | 1. Check that the power cord is plugged in. 2. Test the wall socket with something that works. 3. If the display is plugged into the computer, check that the computer is on. 4. Check the video cable and thumbscrews. 5. Check the cable between the main deflection board and the control panel board. 6. Replace the board module. | 5 |
| Screen flickers | 1. Check the cable connections. 2. Move the display to check for interference. 3. Keep other monitors at least 18 in (46 cm) away. 4. With a video card, set the refresh rate above 60 Hz. 5. Check items 1-4 again. 6. Replace the board module. | 6 |
| Screen blurred | At the highest resolution some small text may look soft; try another resolution. 1. Adjust the two Focus controls on the flyback with the Display Service Utility focus pattern for "Multiple Scan 720/1705". 2. Check focus again. 3. Replace the board module. | 7 |
| Raster too bright | 1. Adjust brightness and contrast. 2. Check and if necessary adjust the B+ voltage. 3. Adjust the Screen control on the flyback. 4. Replace the board module. | 8 |
| Colours too green, red or blue; screen unreadable | 1. Check Color Control in the OSD. 2. Try a known-good monitor on the computer's video port or card. 3. Check the video cable and thumbscrews. 4. Replace the board module. | 9 |
| Raster too short, tall, narrow or wide | 1. Select Recall in the OSD. 2. Adjust width and height. 3. Check the user controls again. 4. Replace the board module. | 10 |
| Raster not centred | 1. Select Recall in the OSD. 2. Move the display to rule out its surroundings. 3. Adjust horizontal position; if it runs out of range, set the raster centre with SW701. 4. Adjust vertical position. 5. Check items 1-4 again. 6. Replace the board module. | 11 |
Voltage checks
[edit | edit source]After a board module change, or for a raster that is too bright, Apple checks the B+ supply at the cathode of D951 on the main deflection board: it should be 175 V DC ± 0.5 V, set with VR901. The high voltage, measured with Apple's probe 076-0392 under the anode cap, should read 25.5-26.5 V on the meter, which Apple gives as 26 kV ± 0.5 kV. It cannot be adjusted; if it is out of range after the module has been changed, Apple's answer was a whole-unit exchange.[1] The full procedures are in General Maintenance.
Related pages
[edit | edit source]- Apple Multiple Scan 720 Display
- Apple Multiple Scan 720 Display General Maintenance
- Apple Multiple Scan 720 Display Service Source
- CRT Discharge Procedure
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Apple Computer, Apple Multiple Scan 720 Display (Service Source), 1997, hosted as File:Multiple scan 720 display.pdf (see Apple Multiple Scan 720 Display Service Source). PDF page numbers: Hot Issues pp. 3-6; Troubleshooting: General p. 28, First Checklist pp. 29-30, No Raster pp. 31-32, Video pp. 33-36, Geometry pp. 37-38; Adjustments: Non-User Controls pp. 82-107.