The Low End Mac Mailbag

External Video Options for a G3 iMac

Dan Knight and Kris Finkenbinder - 2007.07.25

Kris Finkenbinder says:

Hi Dan,

I have been blessed with an opportunity to mess around with an iMac G3 in order to move a stalwart family of Mac users into the 21st century. During the entire lifetime of this machine, they've been using Mac OS 9.0.3(!), and they have several "classic" applications from antiquity that they've been using for years and want to keep using, so it wasn't too difficult to talk them out of springing for a brand new Intel iMac which (surprise!) would not run any of their old applications.

And no, there are no OS X replacements for things like PageMaker 5.0/6.5 and a couple of the other oddball applications they've been using for years, although I'm helping them move on in other areas. So I get to install a big (and quiet, what's with old screaming hard drives?) hard drive, max out the RAM, and set them up with an OS X + Classic environment system that will work just great for them.

The machine is one of the iMac DV+ models, it seems to be the 400 MHz version that came with a 13 GB hard drive and a translucent "graphite" case. I was overjoyed to find out that it had FireWire ports and a VGA-out port. A couple of years ago I upgraded a pair of earlier 350 MHz iMac models that had neither of these port options, which made things much more complicated.

At the same time, I found out about the iMac G3 firmware issue the hard way after merely booting from an OS X installation disc. I saved one in time with the 4.1.9 firmware update, but it took me a year or two until I finally learned how to resurrect the one that completely died on me. I finally did work some sort of magic involving a lot of rebooting and drive swapping, and now they are both chugging away just fine in an office running Panther [OS X 10.2.x] with fast 80 GB hard drives and 1 GB of RAM.

I will probably update them to Tiger sometime soon just for continued software compatibility and access to security updates during the coming reign of Leopard. How unfortunate that Tiger will be the last version of OS X they can run, unless the XPostFacto people can work some magic of their own.

Anyway, my question to you, your staff, and/or your readers concerns the capabilities of VGA-out port on the back of this iMac DV. The internal display of this machine is, of course, getting a little dim and fuzzy from years of use, and really only looks acceptable at 800 x 600, whereas it can natively support 1024 x 768 on both the internal and external display. I happen to have a decent 17" CRT monitor that I can sell these people for next to nothing. I tested the port, and it does work, and it looks great at its full resolution on the larger external display. I'd like to offer to set them up with this external monitor. Having the higher resolution and larger display really enhances the usability of the system, especially for web browsing.

Since this VGA-out port is only capable of mirroring the internal display, there will be no point in having the iMac taking up space on top of the desk along with an equally massive 17" CRT monitor. Being able to stick it under the desk would be great; they have plenty of room to do this without crowding it or kicking it, and with their NewerTech miniStack v.2 combo USB/FireWire external drive they will still have easy access to all the USB and FireWire ports they need.

At the same time there is no reason to have the internal display constantly running, using up electricity, creating excess heat, light and static while displaying the same image as the external monitor. Unfortunately, the iMac doesn't seem to see the external monitor in any way that would allow it to be controlled separately from the internal display. Brightness controls, energy saver preferences, screen savers - everything is software based and will, of course, affect the external and internal displays identically.

So, starting from this information, I have a couple of questions. I've Googled around but didn't come up with any relevant answers to these specific issues:

  1. I am wondering if anyone knows of some obscure OS X system file or command (or Open Firmware command) that could be used to selectively (and reversibly) disable only the internal display while still allowing uninhibited use of the external monitor. I know that the internal display can be physically disconnected from the logic board, but I am loath to open the top cover and make that kind of physical change because it would be difficult for the owners to reverse.
       A software command would hopefully be much easier to change back if necessary without dismantling anything, and I know that with its strong relation to Unix some interesting things can be done in OS X with hardware sometimes just by issuing a shell command or two, like "sudo mv /dev/internalvideoport /dev/Xinternalvideoport". But, and I'm making only a semi-educated guess here, I'm guessing that this will be possible only if the operating system or firmware sees the internal and external display as two separate devices at some deeper level. No indication of this shows up in the display preferences.
  2. If I do physically disconnect the internal display's video cable, is there some kind of circuit I need to keep connected in order to avoid the "headless Mac" syndrome, or will it still work okay as long as the external monitor is connected when it boots up? Is the connection between the internal and external display ports just a physical splitting of wires, or is there some kind of circuitry in between the two that will cause me problems?
  3. I'd also like to disconnect the power to the internal display. Is there any reason why this would cause any problems? Is there any chance the system will refuse to boot up or refuse to activate the external VGA port if the internal display power is disconnected?
  4. I first read about the Dr. Bott gHead VGA adapter a couple of years ago, when researching running a Power Mac G4 as a headless server. I would be very interested to know if anyone has hooked up a gHead to the VGA-out port of an iMac G3, either with or without the internal display disconnected. I'm wondering if the gHead would allow the external monitor to be driven at even higher resolutions like 1280 x 1024, beyond the supposed maximum 1024 x 768 resolution on this machine. Or would the gHead device just be superfluous with an external monitor hooked up?

I can't seem to find any information on the actual maximum resolution of the built-in ATI Rage 128 VR (8 MB, AGP 2x) video chipset, so I have no clue whether it is being restricted to 1024 x 768 only by virtue of being connected to the internal display, which may be telling the graphics system that it can't display any higher resolution, or if there is some hardware limitation in the chipset itself. All the information Google came up with seemed to relate only to retail AGP cards.

I have read somewhere that the gHead is capable of convincing most video cards to allow the use of many more resolutions and refresh rates than they would normally allow when directly connected to most VGA monitors, making it useful even for non-headless usage. Has anyone tried it on a G3 iMac that you know of? If this little machine could support 1280 x 1024 on an external, that would be a fantastic enhancement. I'm sure a widescreen monitor is out of the question with such an old card, but SXGA support would be great.

Anyone who has more information on this can email redbear (at) redbearnet (dot) com, with "iMac G3 VGA" in the subject line to help me identify it (I get a lot of junk mail).

Thanks again for your helpful website. Too bad about Leopard and G3s, but we'll see what the situation looks like a year after Leopard is released.

Kris Finkenbinder
(the long-winded G3/Leopard ranter)

Hi Kris,

Congratulations on your successful updating and resurrection of these iMacs.

To the best of my knowledge, there is no way to support two separate displays using the ATI Rage 128 VR inside these iMacs. Whatever is displayed on one monitor will be mirrored on the other.

There should be no reason you can't disconnect the internal video connector and power supply, and after doing so you may be able to select resolutions the iMac's internal display doesn't support. Either way, a 17" display at 1024 x 768 should look a lot better than a 15" one at the same resolution.

I don't know much about the gHead adapter, but I'd suggest disconnecting the internal display and trying an external monitor before investing in the adapter.

Maybe some of our readers can share their experiences as well.


Thanks, Dan. There's nothing better than bringing a computer that you thought was dead back into a useful life, especially when it can run OS X.

Well, yet another "ancient" iMac G3 is running Mac OS X shockingly well after a simple hard drive and RAM upgrade procedure. I already tried the very thing you've suggested, which was just disconnecting the internal display and attempting to boot with just the external VGA display connected. Unfortunately the machine wouldn't even boot up without the internal display cable attached. Or it sort of seemed to power on but never really seemed to come up in any useful way, and never activated the external monitor. It seems that the CRT iMacs were designed to require the internal display to be connected and functioning before they will work properly.

I don't have the electrical/wiring skills or special connectors necessary to do the sort of hardware modifications that others have done in online articles I have found in order to bypass this limitation, so I finally gave up on the idea and just told the owners they would have to cover the built-in display and live with it as the price of having a much better, higher-resolution picture on the external display. They seem to be fine with that so far. The improvement is really stark when comparing the two displays, especially in terms of accurate color and brightness. The internal CRT is too dim to really display white anymore, no matter how much you fiddle with color profiles.

It also seemed like in all those online articles where someone built their own custom video adapter cable they had a very difficult time getting a clear image on an external monitor, and that's exactly what I didn't want, so that was another reason I gave up on even trying to make my own cable. I have no doubt that the gHead would make no difference whatsoever unless it could either be hooked up directly to the internal display connector - or the internal connector could first be patched in a way that would accomplish the same purpose and fool the system into thinking a display capable of higher resolutions was connected internally (which would thus theoretically enable the same high resolutions on the external connector even without a gHead).

I'm actually kind of surprised that none of the people who really understand how to do these things (and have the wiring and soldering skills required) haven't tried using a gHead. It would be absolutely fascinating to find out that all those old iMac G3s (350 MHz and higher) could have their aging internal CRTs completely disconnected or removed and support using an external display at 1280 x 1024, or even a low-res widescreen resolution. The machines themselves will continue to be useful for basic word processing, email, Web browsing, and other simple office or household tasks in many cases for long after their internal CRTs have failed or faded into unusability. With 8 MB of video RAM there really isn't any technical reason for the card not to be capable of at least a standard aspect resolution of 1280 x 1024. If I remember correctly, even back in the day of 1 MB video cards they could often run at that resolution in at least 256 color mode if not better.

Of course, even if higher resolutions are really impossible in hardware, it would be helpful to have an easier way to disengage the internal CRT without major surgery and handmade special video connectors (along with the "minor" task of modifying the power supply system if you actually want to physically remove the CRT). I don't suppose anyone out there is interested in making small quantities of those special video connectors for sale? There are a lot of iMac G3s out there, and their CRTs are getting very old, dim, and fuzzy. I'm sure many of the CRTs have already failed, causing the whole iMac to be unnecessarily declared dead and discarded. That's always a sad fate, especially for a Mac, when the machine could probably still be serving a purpose for years to come.

Ah well, at least there are also a lot of G4 Power Mac systems out there to keep running into the future.

Kris Finkenbinder


I've been inside the old tray-loading iMacs many times, and all you need to make them work with an external display is a Mac DB-15 to VGA adapter. This makes it relatively easy to disconnect the internal display and wire in an external monitor. I've even heard of people mounting an iMac motherboard inside a 20" display.

Not so with the slot-loaders. One modder,cryogenius, managed to make a VGA cable to connect to the motherboard video on a slot-loading iMac and soon discovered that monitors with cables over about 3' long had serious sync problems. From your email, it seems this is the only way to bypass the internal display - or remove it entirely.

If anyone makes a slot-loading iMac motherboard video-to-VGA connector, I haven't heard of it. It would be a great way to salvage old G3 iMacs after monitor failure, and it may well allow higher resolutions than the internal 15" display. I've sent an email to cryogenius asking if he's been able to go beyond 1024 x 768.


Aaron (a.k.a. Cryogenius) writes:

...after doing one of these conversions, it's possible to use something like Super Res or SwitchRes and experiment with resolutions and refresh rates and see what happens. I wouldn't recommend experimenting with it on an unmodified iMac, however, because I suspect that something in the original power supply or display board can be blown up fairly easily . . . and then the conversion becomes a necessity!

Hi Dan,

Press releases often make it sound like a product is some new item exclusive to that vendor, and sometimes it is, like with NewerTech's products, so I was very pleased to find an alternate source for that same fantastically adaptable piece of hardware with better pricing. If I had the cash, I think I would have already bought several of those enclosures. Quad interfaces on a notebook drive enclosure? Talk about covering all the bases. Now we just need one that also has a Gigabit Ethernet port and built-in SMB/AFS file server capability. Seeing such a device would honestly not surprise me at this point.

The iMac has been safely back in the owners' hands for a while now with a 160 GB internal drive (of which it can see 128 GB, of course) [see How Big a Hard Drive Can I Put in My iMac, eMac, Power Mac, PowerBook, or iBook? - ed] and a NewerTech miniStack v2 external drive for physically redundant backups. That should take care of them for backups, which are handled on an automatic schedule by SuperDuper!

I didn't have the time to mess with the graphics issue any longer, so they will just have to make do with the improved 1024 x 768 on the external monitor. That by itself makes a world of difference compared to what they used to have.

I also set them up with a powerful Belkin UPS, but I have been irritated to find that unlike the other Belkin units I've had experience with, this model has very poor compatibility with Tiger.

The UPS does not show up in the Energy Saver preferences, even though it has a USB connection and the USB bus shows that there is a "USB to serial converter" plugged in when I look in System Profiler. The problem seems to stem from the unit being one of the "Enterprise" models rather than a lower-end consumer oriented model. The consumer models show up in System Profiler as "UPS" on the USB bus. How about that. Apparently the Enterprise models use a different communication protocol. Of course.

The software from Belkin is Java-based and looks as if it was written for 10.2/Jaguar and hasn't been updated since. The software agent doesn't load at startup, probably due to the changes in the startup system in Tiger. I was able to get it to load up by using Lingon to create a launchd plist. That allowed me to at least run the monitoring software, check the status, and change some settings.

The final problem is that the software seems totally incapable of shutting down the system on its own. It brings up messages saying it's telling the workstation to shut down, but nothing ever happens. Then after the designated 2 minutes given for the workstation to shut down, it powers itself off with the computer still up and running. Very bad behavior.

So that's how I spent my Saturday evening, struggling with a UPS unit that should have been plug-and-play with OS X. This has been one of my biggest frustrations, trying to find hardware that actually works with OS X out of the box. Nowhere have I found any list that covers which UPS models from which manufacturers will actually work with the built-in UPS recognition in versions of OS X from 10.3.3 onward.

APC is always at the top of everyone's list, but Belkin models are typically almost half the price for the same capacity. I have no idea about other brands, and even with APC you're rolling the dice because they have multiple different communications protocols. Some work with OS X by default and others will require the APC software, which apparently is much better than Belkin's offering.

This compatible hardware issue extends to other hardware too, like which digital cameras and scanners are compatible with Image Capture. I just recently learned that Image Capture has apparently had the capability for a while now of controlling some digital cameras and sharing access to scanners and cameras over a network. This could potentially be very useful in many small offices, where you could not only have a central print server but also a central scanner server that everyone could access. But where is the compatibility list that definitively shows which hardware will work with Image Capture and allow these capabilities? The lists found on Apple's website are pathetically short and never get updated, and I've found no user lists regarding Image Capture compatibility.

Then there are add-in cards for Mac notebooks and desktops. Which types of cards are still Mac-specific, besides video cards? If something on doesn't explicitly state that it's Mac compatible, will it still work? USB, FireWire, SATA, ethernet cards - are they all compatible by default? In many cases, yes, but there is no reliable way that I know of to determine for sure besides trying it, so I tend to stick with ordering such things from places like OWC so that I know with certainty that the device will be fully compatible with a specific Mac.

I do know that most wireless networking and EVDO cards are still not Mac-friendly. Some USB network adapters work, most don't. So on and so forth. It's a mine-field of guesswork.

This is really one of the biggest problems I'm facing as a proponent of Apple computers, and I have yet to find a reliable source of hardware compatibility information. There seem to be at least three things happening in the Mac world that contribute to this problem.

One is that Apple does absolutely nothing to help users figure out exactly how certain parts of the system work (like the hidden UPS compatibility) and describe exactly what hardware specifications to look for that indicate compatibility. If you happen to plug in a compatible UPS it shows up and works as if by magic. Otherwise, it doesn't. Are there specific UPS protocols that are compatible? Who knows?

Second, companies that make and sell products for Macs don't bother to specify which products are actually 100% functional with OS X. Even when they do indicate compatibility, it is never to be trusted. I got this Belkin UPS from MacMall; one would think it would actually be compatible with Macs.

Third, the Mac users that do have knowledge about which hardware works just seem to assume that all Mac users have this information and don't bother to try and catalog the specifics anywhere. So adding hardware internally or externally to your Mac ends up being a crap shoot in many cases. Every individual Mac user is on their own.

Just ranting a bit, of course, but if you do know of some good solid sources of hardware compatibility for Macs and Mac OS X, especially regarding specific UPS models, I would be very glad to hear about it. It causes me massive headaches when I'm trying to get my clients set up with the right hardware accessories at reasonable prices. A good UPS with the ability to automatically shut down your computer is just one of those things I consider a necessity, like a backup drive, and it pains me to no end to be unable to make a reliable recommendation on affordable UPS models that will actually work without an epic struggle with broken software.

Kris F.


Thanks for all the info. I'm glad the iMac is working so nicely with an external 17" display. Too bad Apple never thought of including a way to disable the internal monitor. And SuperDuper! is a great choice for backup. I've been using it for years.

I've run into the same problem with UPSes. I have a nice Tripp Lite one under my desk, and it's connected to my Power Mac via USB. Energy Saver recognizes it, but I don't trust the power level readings. Another problem is shutting down if you have a program with an open, unsaved file. There should be a default behavior for saviing with a special name. Instead, the Mac simply refuses to shut down, undermining the utility of auto shutdown as UPS power diminishes.

Another bugaboo is UPS power ratings. As UPSes have become smaller and cheaper over the years while seeming offering the same level of power, something must be up. (As I have so many devices, I have a second, smaller UPS to power my wireless keyboard, USB hub, and a few other smaller peripherals.)

Hardware compatibility is a big bugaboo for Mac adopters. At least prior to the Intel transition, you had to make sure a video card was designed to work with the Mac. USB cards that don't specify "Mac compatible" are a crap shoot. Some ethernet and WiFi routers and switches don't support the AppleTalk protocol, which is important for older Macs, older printers, and the like.

Someone ought to create an online database or wiki for this.

Thanks for helping other enjoy the Mac experience, even if the process of getting everything working for them is sometimes frustrating.


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Dan Knight has been publishing Low End Mac since April 1997. Mailbag columns come from email responses to his Mac Musings, Mac Daniel, Online Tech Journal, and other columns on the site.

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