kimac: Fixing iMac(CRT) firmware/OS X problems

Last Modified: Feb 22, 2011 5:43 PM
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I didn't update the firmware on my iMac before trying to install OS X 10.2 or higher on a slot-loading iMac. How do I fix resultant bootup or screen problems?


This topic is a summary of a fuller article which can be found here. It applies only to slot-loaders, not to tray-loaders. How to differentiate between models

The latest firmware for slot-loading iMacs is 4.1.9. If OS X (including Utilities CDs based on OS X) goes anywhere near an iMac with an earlier version then peculiar screen problems may be caused, or the iMac may not start properly. Often it is possible to fix these problems. This topic explains how.

All users who have installed OS X on a slot-loading iMac should make sure their firmware is at version 4.1.9. Otherwise problems may arise at any time even if the iMac is currently working.

If you are having problems then
b do not reset the PRAM
until the firmware is updated, as doing so can make the problems much worse.

To fix the problem you simply need to update the firmware. If your iMac is not behaving properly this can be a little tiresome, but usually not impossible.

b Symptoms

The symptoms are well known and many users have experienced and overcome them:

* S0: OS X installation attempt fails; there may be a message "you need to update the firmware"; the iMac freezes (often with a grey screen); the CD is stuck in the drive

* S1: the iMac starts up but the screen is blank

* S2: the iMac starts up but the screen is dark and a strange colour

* S3: on power on or a restart, the green light comes on but nothing else happens

* S4: after the startup chime the iMac turns itself off after 7-10 seconds

b Overcoming the symptoms

i S0: To get the CD out,
find the emergency eject button inside the right-hand end of the CD slot. Hold it in with a paperclip during power-on. (NB this then disables the CD drive till next power-off.)

i To get round S3,
remove the power cord between reboots.

i To get round S1,
after the iMac has booted, briefly press the main power button to send the iMac to sleep. Wait for the button to pulse orange, then press any key on the keyboard. Usually you will now have symptom S2.

i If you have S2 or S1
and a 400 MHz iMac or later, there may be a VGA connector under a small panel close to the memory access panel on the back of the iMac. Many PC monitors will work if plugged in here.

i If you have S4
then check the suggestions in the full problem solver.

b Upgrading the firmware

The firmware resides on the logic board in non-volatile RAM. To install the latest version (4.1.9) and hence fix the iMac's problems, you first need to boot OS 9.1, or 9.2.x from a local HD. If you have 9.0.x then you can download the 9.1 update from the Apple site.

Make sure you follow all the installation instructions carefully.

Once the firmware is updated (but not before), it's often worth doing an additional PRAM reset: on startup, hold down Apl-Opt-P-R and wait for the second chime.

The most stable version of OS 9 is 9.2.2, so now download and install these updates: 9.2.1 and 9.2.2.

If you need further help then contact Apple Support, read the full problem solver, or post a new topic in the Apple Discussions iMac(CRT) Usage forum.

i With thanks to all contributors.

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