Repair manual

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Welcome to the iMac CRT video/firmware problem page

Disclaimer: while the information here is presented in good faith, we take

no responsibility for errors or omissions, for damage caused to your iMac

or for injury caused to yourself if you try the suggestions described here.

Although some of the information on these pages was obtained from

http://discussions.info.apple.com, Apple Computer in NO way endorses

the information included in these pages.

Introduction

If you have ended up here then you probably have a display or startup

problem with your CRT iMac. This page is primarily dedicated to resolving

problems caused by installing or attempting to install Mac OS X 10.2.x

(Jaguar) or 10.3.x (Panther) on iMacs whose firmware has not been

updated. The suggestions may also be of use in other circumstances, e.g.

if you are experiencing similar problems while running OS 9. We also

mention a couple of similar but unrelated problems and some other

helpful fixes you may need on the way to getting your iMac back to life.

The tell-tale symptoms we are concerned with here are usually some or all

of:

1. iMac starts up but with blank display

2. iMac starts up but with dim or strangely coloured display

3. iMac does not respond following a warm reboot/reset (LED shows

green but nothing happens)

4. iMac turns itself off 7 – 10 seconds after power-on, even if the

power cord was pulled and replaced

If you are having any of these problems then don’t reset the PRAM (Alt-

Apple-P-R on startup) until the firmware is up-to-date, or you may find

yourself suffering from problem 4. This can be difficult to fix, but has been

done on numerous occasions. It’s also a good idea to avoid unnecessary

reboots. While a firmware update can often solve all these problems, if

you only have some or all of problems 1 – 3 the process is usually

relatively simple provided you proceed carefully.

In general, we would encourage all OS 9 users to upgrade to OS 9.2.2 and

upgrade their firmware anyway. This is the most stable pre-OS X

configuration. If you are thinking of upgrading to OS X 10.2 or higher, it is

essential to update your firmware.

Latest firmware versions:

1.2 for the early tray loading iMacs (233 – 333 MHz)

4.1.9 for the slot loading iMacs

Summary of content (11 pages)

PAGE 1
Welcome to the iMac CRT video/firmware problem page Disclaimer: while the information here is presented in good faith, we take no responsibility for errors or omissions, for damage caused to your iMac or for injury caused to yourself if you try the suggestions described here. Although some of the information on these pages was obtained from http://discussions.info.apple.com, Apple Computer in NO way endorses the information included in these pages.
PAGE 2
Before going any further we suggest you print off this page and sit down with a cuppa. Read, mark, learn, and inwardly digest. There is probably more information than you want or need, and some of it is almost certainly inaccurate; it will be too complex for some and too simple for others; but your best chance of finding a fix is to understand some of what has gone wrong with your iMac. So either read on … or take the iMac to your Apple service centre.
PAGE 3
update; your precise symptoms (see below); and any other information you think may be relevant. Please give as much detail as you can. We want to help everyone with these problems but unfortunately don’t have enough time (this is not a paid job for any of us! If only!) so do please help us to help you by reading this document before you post in the forum, or you will be summarily despatched back here.
PAGE 4
S4. iMac turns itself off 7 – 10 seconds after power-on, even if the power cord was pulled and replaced. You will probably hear the hard drive spin up briefly, and the screen (or external monitor) may come on momentarily. You will probably not hear the “thump” of the CRT coils loading up/relays switching nor the crackle of static which can sometimes be heard as the high tension voltage builds up in the CRT. The symptoms may vary and be experienced in combination.
PAGE 5
Firmware versions The latest versions are: 1.2 for the early tray loading iMacs (233 – 333 MHz) 4.1.9 for the slot loading iMacs 4.1.9 can only be installed if you have booted OS 9.1 – OS 9.2.2 from a local hard disk.
PAGE 6
For tray loaders just use the link above to version 1.2 firmware (does the firmware fix problems for tray loaders or only slot loaders?). If you are running OS 9.0.x on a slot loader, you first need to upgrade to OS 9.1. To do this, boot from your original OS 9 CD (hold down “c” during startup) and then run the updater, or follow the instructions in the linked web page. Firmware 4.1.9 only installs on a slot loader which has booted OS 9.1.x or OS 9.2.x from a local HD.
PAGE 7
mac or you might be able to connect another compatible HD). Make sure the firmware updater is fully unpacked and ready to rock and roll. After the iMac has started up OS 9.x and the firmware updater has started (and HD activity has stopped), press Return a couple of times to accept the licence agreement and to accept the system shutdown. Then restart the iMac using the programmer’s button, as described in the firmware install instructions. The update takes a couple of minutes after the long beep.
PAGE 8
b) Leave it switched off with the power cord disconnected for 24 hrs (leave the power cord in at first for 10 mins is this enough?. This should allow the CRT to discharge) c) Reset the PMU. In the slot-loaders this can be reached from the memory access panel. With the iMac on its front and the panel open, the PMU is about an inch SW of the LH edge of the lower memory slot. It is about 7mm square and 3mm thick. The reset button on the top of the PMU is about 3 mm diameter.
PAGE 9
Finally I restored the video cable and power and the iMac booted up smoothly. (Another user merely had to unplug and restore the video cable and the problem was resolved for good.) We are not certain why this works but some sort of a reset seems to be triggered which is enough to get things going again. f) (This applies only to slot loaders with Rev 2 PAV board) Another method is to change the CRT screen type selector briefly to fool the PMU.
PAGE 10
• disconnect power, remove memory and Airport cards, remove battery. Replace battery, PMU/CUDA reset, replace memory (one card only, pref.
PAGE 11
• Apple official memory specifications (NB higher memory capacity can be achieved with modern memory cards) • Firmware compatibility listing for OS X • Complete listing of iMac firmware updates • MacWorld – disassembly of tray- and slot-loading iMacs • Tray-loading iMac CUDA reset • Slot-loading iMac PMU reset • Replacing the battery on a tray-loading iMac (1) • Replacing the battery on a tray-loading iMac (2) • Battery for iMac • How to fix a dim iMac CRT • Disassembly of slot-loading