iMac G4 lampshade will not turn on. Tried PRAM battery change, PMU reset.
Here's the full unabridged problem description: I have a flatscreen 800 MHz "lampshade" iMac, with no upgrades other than an Airport card (not even memory). Recently I reformatted the drive and attempted to reinstall base software from restore CDs. One of the CDs appeared to be unreadable, so I intended to reinstall from the OS X 10.1 CD. At some point (I don't remember exactly now) it rebooted, or asked me to, or I turned it off (but not in the middle of installing something). From that point onward it will not turn on, no exceptions. There is no chime, no fan noise, no hard drive noise, the white LED on the LCD frame does not energize, nothing.
I checked the G4 iMac "won't turn on" apple support page with no success. I suspect that this page intentionally excludes PMU resets, battery replacements, etc. because the G4 iMac is relatively difficult for a consumer to work on vs. other models. I suspected the power cord or the switch. But the cord showed 120V AC when plugged into the wall and not the computer, and after disassembling the case, the power switch leads on the bottom circuit board showed a resistance change when the switch was pressed. I checked for but didn't find any obviously fried components, smoky smell, or charred areas on the bottom circuit board. I don't know if there's another board above the Superdrive and hard drive, so I didn't try to check up in there. I don't have tools for - and am a little wary of - checking for voltages with the unit disassembled and plugged in. Not only that, I don't know what voltages should be present where, and there also appears to be a black connector that is intentionally designed to disconnect when the case is disassembled.
After more net research, I found the apple support page on resetting the PMU. I tried that with the power cord unplugged, with no effect. Some users on apple and macfixit suggested on existing posts suggested that a dead battery may cause a unit not to start up, and that four years or so of operation is a typical Li-ion battery life. I've had the unit since it came out in Jan '02. I replaced the battery, but same symptoms. I reset the PMU after replacing the battery, again with the power cord removed. Then after rereading previous posts I noted that the PMU reset procedure says to press the PMU reset only ONCE. Oops.
I would like to get this guy operational, since I can't emulate 9.2.2, but still want to run that for a few things.
Now I have a few questions for anyone who is still reading:
* Is there a circuit board (that I could visually inspect for zapped components) above the hard drive and superdrive? If so, what are the names for the different boards and what boards do what functions?
* What does the PMU do, that a regular power supply doesn't? What does resetting the PMU do? What does resetting it more than once do?
* If you just have time for one question, here goes: is there anything else I can try, besides replacing circuit boards, to revive my loyal little lampshade?
Thanks, Adam
G4 iMac 15" 800 MHz Mac OS X (10.1.x)
I checked the G4 iMac "won't turn on" apple support page with no success. I suspect that this page intentionally excludes PMU resets, battery replacements, etc. because the G4 iMac is relatively difficult for a consumer to work on vs. other models. I suspected the power cord or the switch. But the cord showed 120V AC when plugged into the wall and not the computer, and after disassembling the case, the power switch leads on the bottom circuit board showed a resistance change when the switch was pressed. I checked for but didn't find any obviously fried components, smoky smell, or charred areas on the bottom circuit board. I don't know if there's another board above the Superdrive and hard drive, so I didn't try to check up in there. I don't have tools for - and am a little wary of - checking for voltages with the unit disassembled and plugged in. Not only that, I don't know what voltages should be present where, and there also appears to be a black connector that is intentionally designed to disconnect when the case is disassembled.
After more net research, I found the apple support page on resetting the PMU. I tried that with the power cord unplugged, with no effect. Some users on apple and macfixit suggested on existing posts suggested that a dead battery may cause a unit not to start up, and that four years or so of operation is a typical Li-ion battery life. I've had the unit since it came out in Jan '02. I replaced the battery, but same symptoms. I reset the PMU after replacing the battery, again with the power cord removed. Then after rereading previous posts I noted that the PMU reset procedure says to press the PMU reset only ONCE. Oops.
I would like to get this guy operational, since I can't emulate 9.2.2, but still want to run that for a few things.
Now I have a few questions for anyone who is still reading:
* Is there a circuit board (that I could visually inspect for zapped components) above the hard drive and superdrive? If so, what are the names for the different boards and what boards do what functions?
* What does the PMU do, that a regular power supply doesn't? What does resetting the PMU do? What does resetting it more than once do?
* If you just have time for one question, here goes: is there anything else I can try, besides replacing circuit boards, to revive my loyal little lampshade?
Thanks, Adam
G4 iMac 15" 800 MHz Mac OS X (10.1.x)
