20" iMac, display not working properly, otherwise OK

I have a 20" imac with 10.4.11 loaded, Have had it for about 2 years, no problems at all except occasional wake-from-sleep issue. All of a sudden, the display has quit working properly. The computer sounds like it boots fine, but the display only shows a very deep blue (not black)and the light ind the lower right corner is "on".
I tried holding a flashlight up to the front as some have suggested, and I do not see see anything at all. This would seem to rule out backlighting or screen brightness issues. I have also reset the PSU and the P-ram, also to no effect. Tried booting from the 10.4 disk, also to no effect.
My teenagers won't admit having any problems, but one of them did admit to turning off the system several times using the power button in an attempt to reset AirPort. Any thoughts? the only other easy thing I can think of is the battery, could that be causing this much trouble? do the display cables ever detatch from the MB or anything like that? any ideas greatly appreciated.
Thanks, Eric

Hey Eric,
This is from the Service Source:
"Screen is dark, fan is running and the hard drive is spinning. You may hear the startup
chime as well.
1. Reset parameter RAM. Press Command-Option-P-R during startup before “Welcome to Macintosh”
appears.
2. The system software could be damaged. Start up from the system CD that came with the computer.
3. Remove the user access panel on the bottom of the computer. With the unit powered on, check if a red
LED is visible in the access door. If the red LED is on, power is on. If you don’t see the LED glowing
red, follow the steps under the symptom “No Power”.
4. Disconnect the A/C power cord. Place the unit in the service stand and remove the user access plate.
Press the PMU reset button on the logic board. Refer to “Resetting the PMU on the Logic Board”
mentioned earlier in this chapter.
5. Check for external video. Connect an external monitor to the mini-VGA port. If you don’t have external
video, replace the main logic board. If you do have external video, go on to the next step.
6. Open the bottom housing and verify that all the cables are securely attached. Pay special attention to
the video cable (located near the modem). If the cables are securely attached, go on to the next step.
Warning: Whenever the bottom housing is opened for service, you must do two things:
• You must clean the original thermal film from the surfaces joining the thermal interface layer and
reapply thermal paste to the thermal pipe.
• The bottom housing has four torx screws that must be tightened to at least 17 in.-lbs. If you do not
have a torque driver, you will have to make sure these screws are tightened by hand FIRMLY, BUT
NOT FORCIBLY. Or, purchase the service tool (076-0899) in order to ensure the thermal pipe is
firmly mated with the top base. If the bottom housing is not securely attached to the base in this
fashion, the CPU may overheat and become damaged.
7. Check the connection of the video cable to the LCD flat panel display (under black tape).
8. Replace the inverter board.
9. Replace the LCD display. Important: If you are replacing the display, be sure to install the new display
shield and EMI gaskets that come with the new LCD panel. Installation instructions are included with
the new display panel. Additional display shields/gasket kits are also available separately as a kit, part
#076-0958.
10. Replace the neck assembly
11. Replace the logic board.
12. Replace the power supply board."
In my experience the connectors both on the logic board and on the back of the LCD panel have been known to come loose. I also have a neck assembly here that went bad.
If you need more info email me.
Richard

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Attachments:
scrolling.vi ‏818 KB

20" iMac, display not working properly, otherwise OK

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