iMac G4 flat screen firmware problems

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Joined: Apr 9 2007
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My iMac does not display anything on screen but the backlight is going. I would like to determine if the GPU Fx5200 is functioning from the open firmware. I think the basic POST test is successful. The GPU appears in the "dev / ls" list etc. I would like to know what commands/words can be run to exercise the display to show some basic operation. I have the machine setup with input & output, to & from enet:telnet,IP_addr thru' the network adapter to another PC. Are there any externally loaded and executable utilities that can be run from open firmware other than boot loaders ? Can you get the console CLI running through a telnet connection ? Is it possible to flash the open firmware support code for the GPU ? When I try to boot from OSX disk it appears to be performing a HD test and comes to a stop (CAPS button/light works). Sorry there are a lot of questions, but I am finding it difficult to find this info anywhere else. Thanks for reading.. Brett.

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Jon's picture
Jon
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Joined: Dec 20 2003
Posts: 2804
If you plug in a mini-VGA ada

If you plug in a mini-VGA adapter, then you can plug in an external monitor in mirror mode. Then you'll still be able to see what is going on on the external screen, no matter what is happening to the built-in as long as the GPU is functioning.

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Joined: Apr 9 2007
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Hi Jon I've tried this. VGA

Hi Jon
I've tried this. VGA monitor goes into sleep mode when plugged in to iMac. I tried resetting iMac with VGA connected so it could auto-detect the presence (Dual head PC video cards do this).
Does the VGA output default to a mirror of primary screen ?
I believe I would have to enable the VGA output in open-firmware for it to work there (O-F) but I do not know enough to drive it. But I will try this again while booting an OSX install disk.
Thanks,
Brett.

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Joined: Aug 25 2004
Posts: 1975
yes

the iMac should default to a mirrored setting. Unless you have put in screenspanningdoctor

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Joined: Apr 9 2007
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Hi Jon I tried booting OSX d

Hi Jon
I tried booting OSX disk with VGA monitor attached & it does output to it. Was able to partition/format hard disk from disk utility.
But I have the feeling that this machine does not behave after the power has been disconnected for 1 week (battery is good).
The OF environment variables were set to input output to from enet:telnet,ip etc and this was solid & reliable for days but when it is unused & not powered and I attempt to use it, it does not work correctly. I then have to repeatedly try to cmd-opt-P-R before it finally works.
It could be temperature related. Thanks