Mac Mini HDMI Output Problem w/ LG L246WP

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Mac Mini HDMI Output Problem w/ LG L246WP

NOTE: This appears to be unrelated to the "screen flickering" that has been noted previously.

I'm using a fresh new Mac Mini 2012 with an LG L246WP LCD monitor. The monitor has HDMI, VGA and Component video inputs.

When I attach the monitor to the Mini DisplayPort output, using a Mini DisplayPort to DVI adapter connected to a DVI to HDMI cable, the display functions properly at all resolutions - including the native 1920 x 1200 resolution that I use it at normally. All resolutions are clearly displayed in the "Displays" System Preferences pane. The display looks perfect, functions properly.

When I attach the monitor to the HDMI port using an HDMI cable, the display does not fucntion properly. The display is shifted about 80-100 pixels to the left and about 20 pixels up, creating black bars on the bottom and right sides. Because of this, a large portion of the display is not visible including the menu bar and most of the left side. Additionally, the settings are reduced to "Best for Display" or "Scaled", with resolution options under "Scaled".

This is not acceptable. I had planned on simply using the Mini DisplayPort output as a workaround, since I already have the DVI adapter from an old setup, but I need to use Thunderbolt to access external hard drives for rapid data transfer. One of my Thunderbolt accessories does not have two ports, so I can't simply add the Mini DisplayPort adapter to a chain. The HDMI port needs to function properly with my monitor.

It's important to note that this monitor has functioned properly with many other comptuers running OS X, Windows and various Linux flavors and it hasn't ever done this before. I've tried several different HDMI cables, ruling that out as a problem. I've tried the HDMI to DVI adapter that ships with the Mac Mini 2012 along with two different DVI to HDMI adapters, ruling that out as a problem. I tried attaching several HDMI devices (game consoles, DVD players, etc) and they all function properly, ruling out an HDMI issue as a problem. The monitor functions properly when attached through the Mini DisplayPort to DVI adapter, so it's not a problem with the monitor. I've reset the PRAM already and the installation of OS X 10.8.1 is stock with no modifications or migrated data. I've tried the suggestions on the HDMI FAQ (although there's no "underscan" option available in Displays)

I tried to call AppleCare and after describing the problem I got disconnected with no callback. I started another ticket, described the problem, discussed the previous disconnection, was assured that I'd be called back if disconnected, and haven't heard back in two hours. So I started to dig into the problem in earnest.

This gets pretty technical.

After substantial research, it appears that this issue is related to the EDID that the monitor sends to the computer and, crucially, the way that the driver responds to it. For some reason, the HDMI port is recognizing the monitor as a CEA device instead of a monitor. As a result, it's restricting the monitor's available resolution to the native resolution that the CEA 681 Series Extension describes ("Best for Display") and all other resolutions (including 1920 x 1200) are only available as "scaled". For some reason that I can't discern, all resolutions (even the 1080i and 1080p options) have similar deformities.

I've attempted to fix this by placing an appropriate override file in /System/Library/Displays/Overrides with an edied EDID removing the CEA-enable flag from byte 127 but, even after a reboot, the OS still insists that it's a CEA device and it won't allow me to force it to recognize the monitor as a 1920 x 1200 LCD Monitor.

How did I come to this conclusion and develop the fix? A nearly identical problem description showed up on the following website, with details on how this user fixed the issue:

http://byuu.org/articles/computing/edid

They used a convoluted process that involved dismantling the monitor and flashing the EDID on the monitor itself. It fixed their problem. I'd prefer not to go through that process just because one computer has a problem with it. Frankly, I'd prefer if the new Mac Mini performed properly in the first place.

TL;DR: The Mac Mini 2012 doesn't work right with the LG L246WP through the HDMI output. Everything else works fine with it. This is very uncool. It's most likely to be an issue with the driver for the Intel HD Graphics 4000 GPU that are bundled with OS X 10.8.1. The Mac Mini 2012 won't update to 10.8.2 (yet), so I can't test it.

Anyone have any other ideas? Anyone else using a Mac Mini 2012 (or 2011) with an LG L246WP monitor? Anything simple I've missed?

Mac mini, OS X Mountain Lion (10.8.1)

Posted on Nov 28, 2012 8:48 PM

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Answer 1

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Erik.Hess Author

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Nov 29, 2012 3:43 PM in response to Erik.Hess

Problem Resolved. But it was complicated. And a huge pain in the rear.

TL;DR: I flashed the EDID as described here. This is not recommended for the weary. Ideally, Apple should release an update OS X that will include the updated Intel HD Graphics 4000 drivers that utilize the CEA flag properly.

Here's the detailed version. As mentioned above, this isn't recommended for the weary. An improper (or interrupted) EDID flash can have seriously unpredictable effects on a monitor's performance.

Step 1: Get a Windows PC set up with a floppy drive and find a floppy disk. Use this system to format the floppy as a MS-DOS Boot Disk and copy over the "ddcw" program described at the aformentioned link.

This took awhile, but I was able to cobble together a temporary frankensystem with parts I had laying around. In installed XP and formatted the disk with XP's format tool.

Step 2: Grab EDID data from the monitor, modify it to disable CEA mode at bit 127 and make sure bit 128, the checksum, is appropriate.

This also took awhile. Several graphics cards I tried could not read or write EDID data. I ended up swapping AGP cards in my frankenstein box until I found one that worked - a generic GeForce4 4200.

Once the EDID data was written to the floppy, I edited the text file containing the EDID data to change the last two hex octets from "01 33" to "00 34" (00, to disable bit 127, and 34 is 33 + 1, which satisfies the checksum) and formatted the text file to match the sample included in the EDID_Write.zip file. Your mileage may vary - make sure the checks.

Step 3: Write EDID data to the monitor.

The link above mentioned three options: Easy (monitor's EDID is unprotected - write away!), Hard (monitor's EDID is protected - use service mode to attempt a fix), and Very Hard (monitor's EDID is protected, hardware modification is required).

Luckily my LG246WP simply needed to be put into service mode as described at the link above (menu + power) and once started up in service mode, I simply enabled "Aging Mode" (whatever that means) and attempted a DDCW write of the updated data.

Step 4: Profit!

After doing this, I powered off the monitor and powered it back on with the Mac Mini attached. The display functions PERFECTLY with HDMI out, just as it does using the Mini DisplayPort to DVI adapter.

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Answer 2

BDAqua

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239,495 points

Nov 29, 2012 4:30 PM in response to Erik.Hess

Great work Erik, thanks for the report! 🙂

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Answer 3

Erik.Hess Author

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Nov 29, 2012 4:31 PM in response to BDAqua

No problem, BDAqua. Was nice to have a real problem to chew on and I figured I'd post the results for posterity, since I'm sure other L246WP users will run into the same problems. This sweet old P-MVA monitor inspires zealotry in many of us! 🙂

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Answer 4

BDAqua

Level 10

239,495 points

Nov 29, 2012 5:05 PM in response to Erik.Hess

For double posterity, you can post it on my site also if you wish...

x704.net/bbs

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Answer 5

mrhooks

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7 points

Dec 11, 2012 12:33 AM in response to Erik.Hess

I'm having issues with the same monitor. I'm using it as a second monitor on my Mac Pro, plugged into the DVI port with a DVI to HDMI cable. The monitor works fine with Lion, but with ML, it must be set to 1080p to avoid any weirdness.

I'd like to try this fix, but I don't have Windows. I wonder if DOSBox will be good enough? Then again, I have an ATi card, and that site says AMD cards never work.

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Answer 6

Erik.Hess Author

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Dec 11, 2012 8:38 AM in response to mrhooks

Unfortunately, the EDID writing software only works in a "pure dos" environment, and even then only with a 'compatible' video card, which means you may need to use several different video cards before you find one that works. I was lucky I had a graveyard of computer equipment available to me for this task.

Until Apple fixes their video drivers (if ever) this long, convoluted fix is the only method I know. Took me all day to cobble together parts and find a functional floppy disc, but once it's done it's done.

Out of curiosity, what video card do you have in the Mac Pro? I've only seen this problem in relation to recent Mac Minis and certain older nVidia graphics cards with broken drivers on Windows systems.

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Answer 7

mrhooks

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7 points

Dec 11, 2012 10:34 AM in response to Erik.Hess

I had a feeling that was the case. I'm trying to see if I have any PC-using friends who will let me borrow their computer. I have a feeling I'll be sticking with Lion for a good long while.

I have an ATi Radeon HD 5770.

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Answer 8

Oct 23, 2013 10:03 AM in response to Erik.Hess

I am running into a very similar problem with my LG L246W monitor and my mid-2012 Macbook Air (13"). I am using the 3rd party mini-display port to HDMI adaptor and then have a straight HDMI/HDMI from that to the monitor. Same problem with the screen being shifted and cut off. I put a Dell 2007WFP on via the same connection (1680x1050 19") and it works fine.

I was thinking it might have something to do with the adaptor and will now probably go and buy the min-display port to DVI adaptor (Apple's) and then use a DVI to HDMI cable to connect the monitor. Should work since Erik.Hess reported that DVI/HDMI worked with his Mac Mini.

Now that Mavericks is out however I will probably update the OS and see if it is fixed there first, but thanks so much for this post and workarounds!

Bob H

Minneapolis, MN

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Answer 9

Erik.Hess Author

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Oct 24, 2013 8:24 PM in response to BobH1.3.4.5

HI Bob,

I hope Mavericks fixes this false CEA flag business but I'm not holding out hope. It looks like this is the only monitor affected by this weird glitch - LG may be at fault just as much as Apple - so I'm guessing folks with the L246W / L246WP are going to have to do the EDID writing dirtywork or find another monitor. Luckily this thread is pretty easily searchable, so people should at least find answers easy enough.

I noticed that the byuu.org links above appear to be dead though. The archive.org Wayback Machine does have an archived version of the site, which I'll link below for reference should anyone need it:

https://web.archive.org/web/20130121234855/http://byuu.org/articles/computing/ed id

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Answer 10

Nov 12, 2013 7:03 PM in response to Erik.Hess

Erik,

I bought a t-bolt to dvi adapter for my mac book air and the monitor works just like you found with your mac mini. Mavericks by the way did not correct it.

I don't know if I will go the full route and flash the EDID but this thread was really helpful as now I can at least use my L246WP via DVI.

Bob H

Minneapolis, MN

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Answer 11

yzarc314

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Aug 25, 2014 7:55 AM in response to Erik.Hess

I found an extremely simple way to flash the EDID. It involves putting the monitor in "Aging mode" and using an Ubuntu LiveCD/USB. You can find step-by-step video instructions on my youtube channel. Search for my video called:

"LG L246WP monitor HDMI fix - writing EDID via I2C under Ubuntu LiveUSB "

Here is a quick description:

My L246WP monitor works with a DVI-to-HDMI connection, but when using an HDMI-to-HDMI connection, the screen image is improperly offset. This can be fixed by altering the EDID, which is the metadata supplied to the computer by the monitor. This can be done via software or hardware. A software solution seems to be driver-dependent, and not supported by my drivers.

The EEPROM which stores the EDID is write-protected. Consequently, using i2cset would produce "Error: write failed." I disabled write-protection by disconnecting the appropriate pin on the EEPROM after disassembling the monitor following byuu's excellent instructions, both on the forum and on his archived homepage. Disassembling the monitor was stressful, difficult, and unnecessary!!!

Instead of disassembling the monitor, it is possible to disable write protection by temporarily enabling "Aging mode." A comment by Michael Pitts confirms that this works. "You get into service mode by holding MENU when you press POWER. Then select MENU, you will be able to access the service menu. Turn Aging Mode ON and the chip becomes writable!"

Once write protection is disabled, this video demonstrates how to fix the EDID using an Ubuntu LiveUSB. This should be much easier and more reliable than trying to use an obscure old DOS or Windows program.

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