03-20-2006, 12:18 PM

Recently, I aquired a 12" G4 Powerbook that survived being run over by a car. The only two casualties were the LCD and optical drive. So, I thought I'd just replace the LCD with a compatible screen purchased on eBay, and I'd have a great laptop for cheap.

I was wrong.

The LCD I took out was an LG/Philips SP121X04 (C2). I bought an LP121X04 (B2) off of eBay and plunked it in the laptop. The laptop didn't detect the new LCD. When I plug in an external monitor, I indeed see that Mac OS X does not see any display but the external monitor, even after clicking the "detect displays" button.

So, I did some more testing, tried plugging in the old LCD and hitting "detect displays". After the backlight lights up and a little bit of picture shows on the cracked LCD, I then pulled the 20-pin LVDS connector and plugged in the new LCD. Voila! Clear bright picture!

So, I know that the hardware is compatible, and in fact uses the same protocol over the LVDS connector as the old LCD. However, I am still unable to get Mac OS X (or Open Firmware) to recognize the new LCD.

Does anyone have any ideas about what is happening or how to fix it?

I'm running Mac OS X 10.4.5. The video card is a GeForce FX Go5200, with ROM Revision 2069.

03-20-2006, 01:04 PM

Does it show up correctly in the system profiler?

03-20-2006, 02:15 PM

Originally Posted by Aptmunich

Does it show up correctly in the system profiler?

No.

If I "detect displays" it is not shown in the system profiler.

If I do the cable switch trick, then it shows up as the old LCD (as far as I can tell). The Vendor ID is 0x610, which it says is Apple. The LCD, however is made by LG/Philips. In particular, this one came out of a Dell.

The problem seems to lie somewhere in that initial exchange of information, where the LCD either doesn't report its information correctly, or there is some software issue that refuses to acknowledge the presence of said display.

03-24-2006, 04:27 PM

Well, here's a little update on the progress of this project.

I installed Linux onto the powerbook to see if there was something funny going on with the Mac OS X Nvidia driver. After starting up the X server, there was no display on the LCD, only on the external monitor. So, I looked at /var/log/Xorg.0.log, and found that indeed, the nv driver did not get an EDID response from the LCD. The same was true of the framebuffer driver that is loaded upon booting.

So, this issue is not software, but rather hardware.

Does anyone know if there is a way to force an LCD to return EDID information? Alternatively, does anyone know how to make either Mac OS X or Linux display to a screen in spite of no EDID response?

Any more ideas?

03-25-2006, 05:06 AM

No internal video usually means that a logic board needs to be replaced (unfortunately) might be as simple as an inverter cable but in my experience it has been the whole logic board.

03-25-2006, 11:30 AM

Originally Posted by uncle sam

No internal video usually means that a logic board needs to be replaced (unfortunately) might be as simple as an inverter cable but in my experience it has been the whole logic board.

The strange thing is that there is internal video with the cracked LCD screen, just not with the replacement.

03-26-2006, 08:18 AM

Have you checked macosxhints.com for tips?

03-27-2006, 10:42 AM

Originally Posted by Aptmunich

Have you checked macosxhints.com for tips?

Thanks for the tip, I'm doing that now.

I'm also looking to see if I can force linux to use the internal display, even though it can't automatically detect the display. For any of the linux heads, I'm using Debian Etch, and so I'm looking to replace what xresprobe provides to X.org, since xresprobe just reads what OpenFirmware provides to it, and OpenFirmware is not recognizing the display.

03-28-2006, 03:44 AM

Me say duh?

03-28-2006, 07:21 PM

Originally Posted by Aptmunich

Me say duh?

Okay. So, I looked at MacOSXHints. No help with my problem.

As I've been working through this, I've noticed that not even OpenFirmware recognizes the screen, and that is the biggest problem. The display is not even addressable by the graphics card (under any OS) if OpenFirmware doesn't see it. (you can get at this in OpenFirmware by typing 'dev / ls'. Once you find the Display devices, you can find out stuff about them by typing 'dev <whatever the path is>' and then '.properties')

As I study the LCDs, I see that rev B2 was produced in 2001, while the C2 is a few years later. Do you think it is possible that the protocol by which the LCD reports its display characteristics changed between revisions?

At any rate, I'm now focusing my efforts on a hardware solution rather than software, since that is the only way I've gotten this to work. I've contemplated a 20-pin switch to allow me to automatically switch between connected displays, but I think there's a more elegant solution.

I'm pretty sure that the conncection is based on the DFP connector, with the 20 pins side by side, rather than in a D-type plug. According to DFP, two of the 20 pins are responsible for exchanging information between the display and the video card. So, my plan is now to confirm that and then wire a plug that re-routes the neccessary pins to the old LCD panel to it can tell the video card (and OpenFirmware) how to drive the new panel.

Kinda messy, but it seems the only affordable option left to me.

03-30-2006, 10:41 AM

Sounds like a plan!

Give it a go, and if not sell the parts individually on ebay...
You can get a ton for mac parts.. (the keyboard alone goes for like 70$ here in germany)

04-08-2009, 01:29 PM

I know this is an old thread, but I am having the exact same issue. Just wondering if anything ever came out of this. Thanks.