Repair manual

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. Refer to the repair manual to locate the

selector (which is only present on Rev 2 PAV boards) and in

light of the dangers of working round a CRT monitor be sure to

read the video section in depth.

Remember that either of these methods may damage the CRT, the

PAV board, the logic board, you, …

Last resort

If you have tried all these suggestions without success then you may not

have the firmware problem. However, it is just possible the relevant repair

manual will enable you to diagnose or fix the problem. See also these

suggestions for a dim iMac CRT.

Summary of tips/fixes

• Check firmware up to date; update it if not (OS 9.1 or higher

needed on a slot-loader in order to update firmware to 4.1.9)

• Remove power cable for 10 secs

• Sleep/wake trick, to recover screen display in certain circumstances

• Reset the PRAM by holding Alt-Apple-P-R after the startup chime;

keep holding till you’ve had 3 chimes (best done only when

firmware up to date or it may make things worse); repeat a few

times; try removing power cord afterwards

• (tray-loading) unplug internal video connector; does iMac now start

up? If so, use external monitor

• (slot-loading) try an external VGA (PC) monitor if your iMac has the

access panel at the rear with the VGA video connector underneath

• remove power cord for 1 hour following PRAM reset

• (tray-loading) CUDA reset or (slot-loading) PMU reset

• Replace old battery on logic board (motherboard)