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G4 iMac Screen help

Joined
Sep 10, 2018
Messages
6
Motherboard
g4
I am nearly done with my G4 iMac mod but I can't get the screen to display a picture via HDMI. Huge thanks to dremel junky any everyone else here who has posted detailed guides and pictures of their mod progress. Long story short, I have plenty of electronics exp but I can't seem to get this known working LCD to display a video signal from either a FireTV or Raspberry Pi 3+.

Details: I have a 17" 800Mhz iMac G4 in good working condition. I want it to be a motion activated photo frame near the entry way. Loaded up some custom software on Raspberry Pi, connected it to a HDMI display for testing, works great, time to mod the iMac to house the Pi.

I figured why bother with the DVI connector when they have HDMI connectors with screw terminals, so I ordered one and connected all the wires. Checked continuity and everything appears to be connected correctly.

I'm using the iMac's PSU connected to a few Buck converters to drop the voltage to 5v and 3.3v as needed. I wired up the inverter and its working great. Varying the voltage to the Green wire I can control the screen brightness.

When I connect the HDMI I get various multicolored lines that do not move or change position.

I am using only 5v on the BL/on off for the inverter. I am using 3.3v for the 3 power wires on the LCD cable. I am using the hot plug to connect to the red wire on the LCD cable. I opened up the rear LCD to confirm that the order of the wires was in fact Red, Orange, Blue, Green.

I am now on week 2 of trying to figure this out. Any help or things I could test or try would be super helpful.

IMG_3024.JPG IMG_3018.JPG IMG_2975.JPG IMG_3022.JPG
 
Joined
Sep 10, 2018
Messages
6
Motherboard
g4
I bought a DVI connector and a HDMI to DVI converter and I am doing the mod as shown from everyone else's guides. The screen now shows solid colors instead of lines and I can see the words "Amazon" when connecting my Amazon Fire TV via HDMI. It is soooo close to working. Either something is still connected wrong or something is not making solid connections to the port. It is unlikely that I broke something as I am getting some output. Any idea what I am missing?IMG_3049.JPG
 
Joined
Sep 10, 2018
Messages
6
Motherboard
g4
An update on this. I picked up a second iMac G4, 1.2Ghz for $60 and swapped out the screens and necks. Same results more or less, however this time I did a much better job on the mod. I decided to try different adaptors and cables with no success. Finally I plugged it into my MacBook Pro and... BAM perfect image! Plug it into a Pi, or the Amazon Fire TV... same garbage... No idea why but the only thing different is the source signal. I want to use this with the Pi so I am trying to figure out what the difference in the signal could be. Any ideas?
 
Joined
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I can appreciate that you've done a lot of work to get your configuration functioning, its not easy. I don't understand, however, why you've chosen the connecting block method as shown in your post. Other mods have had success using this part as it is directly pin size compatible with the LCD cable of the G4. Mated up to a DVI to HDMI adapter, you're off to the races. The 17" screen isn't nearly as difficult as the 20" due to the 12v inverter requirement, not 24v as with the 20" variant.

Perhaps worth a try... good luck.

Cheers,
Ersterhernd
 
Joined
Sep 10, 2018
Messages
6
Motherboard
g4
I can appreciate that you've done a lot of work to get your configuration functioning, its not easy. I don't understand, however, why you've chosen the connecting block method as shown in your post. Other mods have had success using this part as it is directly pin size compatible with the LCD cable of the G4. Mated up to a DVI to HDMI adapter, you're off to the races. The 17" screen isn't nearly as difficult as the 20" due to the 12v inverter requirement, not 24v as with the 20" variant.

Perhaps worth a try... good luck.

Cheers,
Ersterhernd
Thanks for the reply!

So it turns out the issue was not with the Mac but rather the source. The Fire TV doesn't support the iMac native resolution of 1440x900 and neither does the Pi! Connecting it to a computer worked because the computer listened to the available resolutions in the initial handshake when connected.

Adding these lines to my Pi config.txt fixed it for me.
hdmi_cvt=1440 900 60 5 0 0 0
hdmi_group=2
hdmi_mode=87
config_hdmi_boost=7

I ended up re-doing the mod with that exact part. Currently I am getting some static when using two different HDMI-DVI converters but my 6+ ft HDMI-DVI cable works fine... lol.

My mod is nearly complete now and I have a second mac that I might be able to convert as well, though I may have toasted the backlight on it. I'm working on a circular ABS motherboard shaped plate to hold all the components neatly inside the mac. If I'm lucky I might be able to get the first G4 up and running as well. The remainder of the parts are going on eBay.

Added pictures of the current state along with a picture of the static in the image.
IMG_3421.JPG
IMG_3418.JPG
 
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