iMac G3 LCD

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impossiblescissors
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iMac G3 LCD

Post by impossiblescissors » Fri Sep 09, 2011 5:17 pm

I've recently come into possession of a 1998-vintage Bondi Blue iMac. The motherboard and hard drive are fine but the unit won't power on, probably due to a burned-out flyback transformer in the monitor. But I also got my hands on a 15" LCD, so I'm thinking about scooping the old CRT out and replacing it with the LCD.

I already know that I'll need to come up with a VGA-Mac adapter cable. But I also had a few questions about the project and I was looking for suggestions:

1) How would I connect the iMac power supply to the LCD monitor to eliminate the need for a second power cable? Would the pins for the internal connection necessarily be the same?

2) Is there a good way to mount the monitor's adjustment buttons so that they'll be functional and concealed? Or would it be better to just tuck the buttons into the case and never see them again?

3) Will there be any thermal issues with the LCD inside the iMac enclosure? I'd guess that the heat will the same as or lower than the CRT.

Apologies ahead of time for treading on similar ground to the impressive iMac-PC thread. I'm looking into whether I can find a similar solution for powering the LCD.

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jdmlight
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Re: iMac G3 LCD

Post by jdmlight » Sat Sep 10, 2011 9:30 pm

impossiblescissors wrote:so I'm thinking about scooping the old CRT out and replacing it with the LCD.
Be very, VERY careful around the CRT. The flyback transformer will hold a charge for years after you power off the computer. There are plenty of guides on how to properly discharge a CRT, quickly accessible via Google. In addition to the high voltages, the tube itself is fragile (particularly the neck), and will implode into a thousand pieces if you break it. Not trying to discourage you in the least, just a warning.
impossiblescissors wrote:I already know that I'll need to come up with a VGA-Mac adapter cable.
False. There's a standard VGA port on the rear of the iMac under a port cover. You should be able to plug a VGA cable into this and still cleanly route it to an internal LCD. In fact, you should try the Gateway monitor you have on this VGA port to make sure that the problem lies with the monitor before going further.
impossiblescissors wrote:1) How would I connect the iMac power supply to the LCD monitor to eliminate the need for a second power cable? Would the pins for the internal connection necessarily be the same?
There's a couple of ways you could go about this. If your Gateway 15" monitor has a power supply board that is separate and can be ripped out, the monitor hopefully would take something standard like 12v. If so, you should be able to tap the 12v from the hard drive/CD drive cable. I think there's enough reserve power on that line that it should work. Alternatively, you could tap the 120v from the power inlet and provide 120v to the monitor. Make sure to use thick enough wire, something like lamp cord would work well.
impossiblescissors wrote:2) Is there a good way to mount the monitor's adjustment buttons so that they'll be functional and concealed? Or would it be better to just tuck the buttons into the case and never see them again?
The only place I could think of possibly hiding the monitor adjustment buttons so they'd be functional yet concealed would be behind the RAM access door or the VGA port access door. Depending on your monitor, you may not need the adjustment buttons. After you have it adjusted and powered on, unplug the monitor for a few minutes. When you plug the monitor back in, does it remember your settings and that you had it powered on? The monitor I used does remember its settings and that it was on, so the adjustment buttons aren't really necessary.
impossiblescissors wrote:3) Will there be any thermal issues with the LCD inside the iMac enclosure? I'd guess that the heat will the same as or lower than the CRT.
Nah, the CRT would produce more heat.
impossiblescissors wrote:Apologies ahead of time for treading on similar ground to the impressive iMac-PC thread.
No apology necessary, you're just pushing me to finish my project. :wink:

Also, are you planning on keeping the original iMac motherboard? Or are you planning on replacing the innards with PC components like I am doing? Or how about a PS3 or Xbox 360 (or a Wii if you could be creative with how to rig up a discrete sensor bar)? Another option would be replacing the innards with a Mac Mini if you wanted it to still be a Mac. Just some options to consider (especially if the problem with it not powering on isn't related to the monitor).
--John (and please call me John, it's really weird to be called by my username)
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impossiblescissors
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Re: iMac G3 LCD

Post by impossiblescissors » Sun Sep 11, 2011 12:20 am

Original idea was to use the iMac motherboard, put Debian Linux on the hard drive, and use it for something useful. As money becomes available I can put in a modern x86 motherboard and Hackintosh it (as a replacement for Gf's mom's aging dual-G4 Mac.)

I don't know about your vintage of iMac, but mine still uses the old DB15-style monitor connector that was used by all Macs until around '98 or '99. (It's a Rev. A.) They might have changed to a standard HD15 (VGA) on later revs. It adds up to a decent headache, but I suspect I can make an adapter cable from the one in the iMac and a spare VGA cable by twisting the wires together (since the pinouts are virtually identical.)

For removing the CRT, I've already checked out the article on the MacOpz website that addresses removing the analog board. I do not think this will be a problem.

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jdmlight
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iMac G3 LCD

Post by jdmlight » Sun Sep 11, 2011 11:54 am

So it's got one of these instead:
Image
My iMac was an iMac DV 400mhz, so a much newer revision. It had VGA.

As far as just wiring up a cable straight from the DB15 to VGA, I don't think that'll work. I could be wrong, but we always used adapters like these:
Image
They have DIP switches on them to set the resolution for the VGA monitor. I don't know how available they are or how expensive they are, but that would be a good solution.
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