When you try to install OS X 10.3 on a stock iMac DV Rev E, the Mac OS X installer greets you with a notification that you need to upgrade your firmware first. When you reboot the machine to do so, you are left with an iMac with a dead display. Trying to fix it with zapping the parameter ram only makes it worse, leaving you with an unbootable machine.
The machine shuts down immediately after video switches on on an external monitor. Apparantly, this happens because the mainboard thinks the PAV board is fried. Chewing on this problem for days, I tried virtually every trick suggested on the internet at various websites and the Apple Support forum. Most of these tricks are based on the attempt to let the iMac re-initialize its hardware. Unfortionately, none of the suggestions worked, even putting the motherboard in another machine or unplugging and replugging hard disk during startup did not wake up the machine. It was time to try to find a solution which was a bit less based on trial and error and a good dose of luck...
We attempted the following : To disable the internal monitor without disconnecting vital signal wires in the internal video connector which are needed for a successfull startup. We assumed that the sync timing is incorrect which causes an unacceptable power consumption in the monitor which switches off the power supply.
Disclaimer : This procedure requires a certain amount of manipulative skills to disassemble the computer. Following the instructions on this page may expose you to electrically charged components of the innards of your computer system. Needless to say you should proceed only at your own risk.
Open up the top of the iMac. WARNING : opening up the top of your iMac reveals parts that are potentially loaded with high voltages. Proceed at your own risk and take the necessary safety measurements such as discharging the CRT. For more information, a detailed take-apart of slot-loading iMacs is available here.
With the iMac screen down, you will see a large metal connector next to the head of the CRT tube, on the right, oriented at an angle. This connector links the mainboard with the analog video board. Loosen the internal monitor connector from the motherboard using a screwdriver and unplug it by pulling the wire gently but firmly.
Now, we will need to be able to patch some of the wires, but not all of them. Doing so is remarkably simple provided you have the required tools. The trick is to use an old Mac floppy disk connector cable and plug it into the connecter from which you unplugged the internal monitor connector from, into the mainboard. The floppy disk connector cable fits perfectly.
Then stick the loose connectors together using a rubber band and make sure the notch of both connectors points in the same direction; then the pinout is identical: top left corresponds to top left, pin numbers are marked on the internal monitor connector. The odd numbers on one side and the even numbers on the other side.
To make the connection, use short copper wires to connect pin 3 (GND, Ground), 6 (5VSB, 5 Volt Stand-By), 10 (PFW, Power Failure Warning), 12 (PS-On, Power Supply On), leave all others open. Pierre Durignieux made a sheme of the pinout and the connections required, you can find it online here.
Connect an external VGA monitor on the iMac DV's VGA port on the back. Then you can power on using the power key on front of the machine. The keyboard power button doesn't work. The video on the external monitor is very bad, but good enough to flash the firmware, and the power doesn't switch off! After flashing, shut the machine down, reconnect the internal monitor and close the case. Flashing the firmware fixes the problem with the bad video and you can continue to install Mac OS X.
Based on information found on :
About the authors
This iMac was brought alive by Bart Denoo and Frederik Vande Rieviere. Bart Denoo is Founding Partner and Chief Software Architect of Artwork Systems N.V. and Frederik Vande Rieviere is System Manager of Artwork Systems N.V.