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Quick question about 15" iMac G4 DVI Conversion

Joined
Sep 14, 2017
Messages
2
Hello all. I've been working on a 15" iMac G4 conversion for some time now. I've gotten around to the display portion and using the various pinouts I've found online, managed to successfully get the backlight (& dimming) working. I am now working on the TMDS portion, but have run into a snag.

I have all my cables connected to a DVI header as per the pinout and instructions on Dremel Junkie's website. I also have the hot-plug detect wired properly. My Windows laptop detects the screen when connected and shows the proper resolution, etc. and attempts to output an image to it.

The screen, however, never changes. It just remains solid white the whole time. For those of you who have attempted similar mods: did you ever run into this issue? Some of my TMDS wires do have slightly damaged sleeves. Could that cause these symptoms?

Before I painstakingly remove all my wires from the DVI connector I figured I would at least ask. Thanks in advance to anyone who might offer assistance.

-SB
 
Joined
Sep 14, 2017
Messages
2
UPDATE: I found the problem. There are several pinouts for the 15" iMac G4 available online. Most are identical but one key difference is that some of them specify 5v for the tmds VCC and some say 3.3v. I was working with the one mentioned on Dremel Junkie's website, which had 5v listed. Apparently this is wrong. After disassembling my LCD and looking at its controller board I found a blown SMD fuse on the VCC input (the turquoise and blue wires on the TMDS connector). I replaced this fuse and changed inputs to 3.3v and got a perfect signal.

TL;DR: The 15" iMac TMDS VCC is NOT 5v as stated on some pinouts-- it is (at least on my unit) 3.3v.
 
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UPDATE: I found the problem. There are several pinouts for the 15" iMac G4 available online. Most are identical but one key difference is that some of them specify 5v for the tmds VCC and some say 3.3v. I was working with the one mentioned on Dremel Junkie's website, which had 5v listed. Apparently this is wrong. After disassembling my LCD and looking at its controller board I found a blown SMD fuse on the VCC input (the turquoise and blue wires on the TMDS connector). I replaced this fuse and changed inputs to 3.3v and got a perfect signal.

TL;DR: The 15" iMac TMDS VCC is NOT 5v as stated on some pinouts-- it is (at least on my unit) 3.3v.
There was a few of us who built 17" iMac G4's a few years back and made this error. Fortunately didnt get stung with a failure before realizing the voltage issue and getting it reworked properly.


Cheers
 

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