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iMac G3 no screen, does not react to any boot ROM keystrokes.

Raov

Raov

macrumors newbie
Original poster
Jan 17, 2021
12
0
Took my iMac G3 out from the balcony, let it rest a bit and heat up to room temperature for a day. Turning the thing on, it chimes, and even boots into the OS, but the screen works only after being put into sleep mode and taken out of it. After around 3 days the issue fixed itself, and it worked every time. Until now. The thing deteriorated on my eyes. First it was the OS install that basically corrupted itself, then I decided to do a full reset (reset-nvram, set-defaults and reset-all though OpenFirmware), and after that it became braindead: chimes, there is high voltage on the CRT, but absolutely nothing displayed. Does not react to any boot ROM keystrokes. Not even a PRAM reset.

What could be the culprit here?
 
Which iMac G3?
Troubleshooting checks are very different between the 2 major generations in the G3, with one identifier being the CD drive.
Oldest generation has a tray-loading drive, and newer has a slot-loading optical drive.
 
DeltaMac said:
Which iMac G3?
Troubleshooting checks are very different between the 2 major generations in the G3, with one identifier being the CD drive.
Oldest generation has a tray-loading drive, and newer has a slot-loading optical drive.
Click to expand...
Oh right, totally forgot to mention.
Mine is a slot-loader G3 400MHz. Drive is broken though, so even if it goes up and running again the only way to install OS X is via USB. I remember trying it once, but now boot picker refuses to select the USB.
 
You also have Firewire. But, you would need a firewire device to do that. I have a firewire external with both Tiger and Leopard installers.
Booting from a USB device needs the Open Firmware commands that allow booting from a USB device.
Some tips for that here - https://idevicecollector.home.blog/...3-g4-or-g5-from-usb-using-open-firmware-mode/

I will guess that your symptoms mean that the graphics chip on the logic board has failed -- but, try replacing the PRAM battery.

Leave power cord disconnected. Remove the battery. Battery should measure between 3.3 and 3.7 volts.
press the reset button on the logic board without the battery installed.
Insert the battery now. Press the logic board reset button once again. Do not press a second time.
Wait 10 seconds, then insert the power cord, and try to power the iMac.

If you get no improvement, I suspect the logic board.
 
Last edited:
DeltaMac said:
You also have Firewire. But, you would need a firewire device to do that. I have a firewire external with both Tiger and Leopard installers.
Booting from a USB device needs the Open Firmware commands that allow booting from a USB device.
Some tips for that here - https://idevicecollector.home.blog/...3-g4-or-g5-from-usb-using-open-firmware-mode/

I will guess that your symptoms mean that the graphics chip on the logic board has failed -- but, try replacing the PRAM battery.

Leave power cord disconnected. Remove the battery. Battery should measure between 3.3 and 3.7 volts.
press the reset button on the logic board without the battery installed.
Insert the battery now. Press the logic board reset button once again. Do not press a second time.
Wait 10 seconds, then insert the power cord, and try to power the iMac.

If you get no improvement, I suspect the logic board.
Click to expand...
Checked the battery, basically completely flat. 0.16v. What type of battery is used? I can probably get a replacement, or do a LiPO mod.

Also, when I start the iMac with clean PRAM, it works, but only until I shut it down. Then it does not respond to any keystrokes. And even when booting for the first time, there is only the chime, and 3 beeps. Read around on some sites, means the iMac can't find a bootloader. Matches my case, so going to assume on the first bootup it works fine.


UPDATE: Just removed a stick of RAM, and it just sprung back to life! Seems like that was the culprit.
UPDATE 2: Reseated the stick back, still boots up just fine. Don't know why I didn't check the RAM.
UPDATE 3: Reassembled the iMac, booted up once and fell back into what I can only call it "braindead state". I'm guessing the PRAM battery is the second culprit here.
UPDATE 4: Cleaned the RAM contacts, seemed to help.
 
Last edited:
DeltaMac said:
Booting from a USB device needs the Open Firmware commands that allow booting from a USB device.
Some tips for that here - https://idevicecollector.home.blog/...3-g4-or-g5-from-usb-using-open-firmware-mode/
Click to expand...
I tried that too, but when doing /pci@f2000000/usb@19/disk@1 OpenFirmware does not seem to understand what in the hell I am doing and throws a "unknown word" error.
And when trying to list directories on the USB, method <dir> not found, ihandle=ffbc5e00 phandle=ff85ff48 DIR method failed gets returned. Any ideas what it could be?
 
Last edited:
I don't have much help for booting to USB. I always use a firewire drive for those purposes..
I do know that you need to be sure the command that you are using in open firmware is correctly typed.
Try searching for other sources for "booting a PPC Mac from USB using open firmware" -- or similar searches. You will find something that will help.
 
DeltaMac said:
I don't have much help for booting to USB. I always use a firewire drive for those purposes..
Click to expand...
I managed to install Ubuntu 14.04 Server in the meantime, it worked straight from the bootpicker.

I do know that you need to be sure the command that you are using in open firmware is correctly typed.
Click to expand...
Yeah, typed in key-for-key.
 
Try this variation:
Code: 
boot usb0/disk@1:,\\:tbxi
Note that there are two backslashes before the :tbxi
 
Did you also try the alternate?
Code: 
boot usb1/disk@1:,\\:tbxi

i have often been frustrated with trying to boot a PPC to USB. Sometimes it works - no problem at all, then the next time, on the same Mac, I have to fight with PRAM resets, etc.
(this is WAY simpler if you have a firewire drive -- it "just works"!)
 
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DeltaMac said:
Did you also try the alternate?
Code: 
boot usb1/disk@1:,\\:tbxi
Click to expand...
oh right, totally forgot the USB might've been on port 2.

i have often been frustrated with trying to boot a PPC to USB. Sometimes it works - no problem at all, then the next time, on the same Mac, I have to fight with PRAM resets, etc.
(this is WAY simpler if you have a firewire drive -- it "just works"!)
Click to expand...
Never had to fight with PRAM resets on this iMac when booting from USB. Literally, plop the USB in and it just works. Even bootpicker sees it.
Probably newer firmware?
 
This is what made the iMac boot from OpenFirmware: boot /pci@f2000000/usb@19/disk@1:,\\:tbxi
It started booting, but Do Not Enter sign appeared earlier than booting from boot picker directly.
 
Yes, the prohibited symbol appears when the system that you are trying to use is corrupted somehow, or simply a system that your G3 iMac can't boot, or not a supported system - such as trying to boot to a Leopard installer.
What system is on your USB disk?
If an OS X installer - exactly which version, if you know that?
 
Raov said:
OS X 10.3
Click to expand...
It's possible that 10.3 doesn't like being booted via USB (I've never tried it but 10.2 doesn't like it iirc) . Can you boot in verbose mode and see if you get anything like "waiting for root device"?
 
Amethyst1 said:
It's possible that 10.3 doesn't like being booted via USB (I've never tried it but 10.2 doesn't like it iirc) . Can you boot in verbose mode and see if you get anything like "waiting for root device"?
Click to expand...
tried passing -v to it by holding V when selecting it from boot picker, nothing.
I'll try to get into verbose somehow though.
 
Amethyst1 said:
It's possible that 10.3 doesn't like being booted via USB (I've never tried it but 10.2 doesn't like it iirc) . Can you boot in verbose mode and see if you get anything like "waiting for root device"?
Click to expand...
I see the problem. There is "not enough power" to configure the USB. Swapped for a powered hard drive enclosure, same thing. Doomed for FireWire?
 
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