mini-ITX Powered iMac G3 projects

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Last seen: 8 years 5 months ago
Joined: Oct 24 2009 - 01:59
mini-ITX Powered iMac G3 projects

I've been wanting to do this for a while, but finally I'm doing it.

Project 1: Grape trayload iMac 333.

Screen is capable of displaying video from alternate source without logic board connected or even installed. However it can only display resolutions that correspond with it's fixed horizontal sync, so 640x480@117, 800x600@95, or 1024x768@75. I think there are a few more, but it will never show the bios post screen on most mini-ITX motherboards. I'll be setting that up with a different screen before final assembly. Afterwards if I need to access the bios I will connect an external screen. Shouldn't be a problem, plus not seeing the bios on boot will make it seem more Mac like.

Power supply capable of powering low power mini-ITX motherboards. I have it running a Zotac ION-ITX-D-E and it works great. I made a custom wiring harness using the pinouts from a link listed in an article on here describing how to put iMac G3 motherboards in ATX cases, so I plug into the iMac's power filter board and then I have a 20 pin atx connector, one sata power connector, and a sata slim drive connector. I hooked up a 500GB seagate desktop drive, and a lite-on slim dvd burner and it powers all of it even though the iMac's power supply is only 80 watts.

The drives will fit in the chassis the same as the originals. The tough part is that I have to trim the part where the motherboard goes in order to get it to sit low enough. I think it will work out though. Then I have to decide how I want to do the video cable since the Zotac board doesn't have any internal video connector. It has an external VGA. One idea was to mount some sort of connector underneath the motherboard that will make contact with the solder pins from the vga connector, and then that way I won't have to have a cable running from the external connector to the iMac's internal video cable.

I've also done a lot of research concerning running OS X on the Zotac Ion boards, and it seems that they are decent. A lot of work, but once it's done, it looks good. The main concern now is that people have found that the 10.6.2 kernel doesn't run on Intel Atom CPUs, so you have to go back to the 10.6 kernel until someone makes a custom 10.6.2 version. Not a big deal.

So, it looks like that one will work out just fine!

Project 2:

This involves doing this same mod with a slot loading iMac G3. I have a few of them to play with, but they are more complicated. I made a few custom wiring harnesses for the video and such, but was only able to power on the power supply. I read in another forum somewhere that the screen on those will only display video if the logic board is drawing power, but I don't know if that means it sense whether power is being drawn from like the 5 volt supply on the down converter board, or if there is a special sense pin for that. The pinouts for the slot loaders are just as well documented, but for the most part only the pins you need for putting the iMac logic board in an ATX case are explained. There are a few labeled pins that they don't use for that mod, but I don't know what those pins are for. I'd really like to do this mod on one of these since they have a 150 watt power supply and could probably run a mini-ITX board with a 775 socket cpu, or even one of the new 1156 socket ones like a core i5 when they come out next year.

So basically I know project 1 will work, and if anyone has any insight on project 2 please leave a comment. I imagine I will try testing it with a draw of some sort hooked up to the down converter board.

eeun's picture
Last seen: 5 months 2 weeks ago
Joined: Dec 19 2003 - 17:34
Sounds like some fun projects

Sounds like some fun projects, and I hope you get some photos posted as the work.

One thing to note is the age of the iMacs, and the rather high failure rate of their analog boards. It would be a shame to do all that conversion work only to have the screen fail, so you might want to consider plonking new screens into both machines. A 15" LCD would give you a lot of room to play with inside the case. Wink

Last seen: 8 years 5 months ago
Joined: Oct 24 2009 - 01:59
I thought about that, but I'v

I thought about that, but I've seen LCD conversions, and I didn't like the way they came out. They're flat so they don't sit right against the opening, and also they're bigger than the opening, which looks weird. A 14.1 inch 4:3 lcd would be the way to go, but those are hard to find, and they're still flat. Plus, once you do that, the conversion is much less challenging, which takes some of the fun out of it. I always feel like the CRT is part of the design too.

iDweeb's picture
Last seen: 2 years 6 months ago
Joined: Dec 19 2003 - 14:45
mini-itx imacs

Wow! it seems like we're on the same page as far as upgrading an imac g3. Right now I'm upgrading a Mac Classic to run an Atom mini itx board so I can run it as a Hackintosh running Leopard. (Ironic, no?)

The reverse engeneering has given me a few ideas on pimping out a G3 imac. I'm mostly in the planning stages on the imac but I'm gathering materials thought would be to look for a used 15 inch CRT monitor somewhere to use as the screen. Gut it and place the donor's screen into the imac case using the existing imac mounting brackets.

An advantage to this option is that the hookup is standard VGA so there's less mod work to do on the signal connectors etc, plus video resolutions aren't as limited as using the imac's own internal CRT if you modify the . You WILL have to spit off a power connection from the 3 prong outlet separate from a PSU and add a separate power switch for the monitor, but those can be placed discreetly most anywhere.

I've looked for a few weeks but I just found a 15 inch dell CRT monitor at a thrift store. The 16 inchers seem to be a lot more common. You'd have to keep your eyes open but they can be had locally for under $5!

That might make the mod a bit cheaper /easier and more "authentic" than a LCD screen.


Oddball's picture
Last seen: 4 weeks 20 hours ago
Joined: Apr 4 2009 - 18:20
Screen Mods

I'm converting a ComPaq Portable II into a peripheral for HP_Mini. I'm planning to vacuum-form plexi over the original CRT with a plaster cast of the (back of the) Bezel/CRT interface as a surround to match the original CRT.

Mine'll just be backpainted black after having gilded/backed up the ubuntu logo before forming the plexi. It's for a swing open door to hide a pair of removable drive cages and prolly some other connections/goodies.

There's no reason this process couldn't be used to front-face a flat LCD to get a perfect match of the unmodified bezel/CRT. It'd be a bubble front over a flat screen, but plexi formed over a CRT's face ought to be crystal clear.

jt =;-D

Last seen: 8 years 5 months ago
Joined: Oct 24 2009 - 01:59
video board

I thought about this as well, but I didn't feel like fiddling with the CRT. I read a lot of articles on how to do it safely, but I'm still scared. The other concern was that the video board on the back of the CRT in the iMac's is styled, and I don't think one from a Dell or other brand would be.

Last seen: 8 years 5 months ago
Joined: Oct 24 2009 - 01:59

I made up a quick HTML 1.0 style page with some pics of the mostly finished tray loader!

DrBunsen's picture
Last seen: 3 years 10 months ago
Joined: Dec 20 2003 - 10:38
Nicely documented :D

Nicely documented Biggrin

Last seen: 8 years 5 months ago
Joined: Oct 24 2009 - 01:59
Next step: Slot loader

So before even really attempting this on a slot loader, I have to first figure out how to get video to work. I made a video cable using the pinouts from this page:

But, although connecting the T5V and PFW wires on the HE20 connector shown there seem to turn on the power supply, no video will show. I need someone to help me figure out what the wire labeled L/S does.

Another test might be to connect the -10V to pin 12, because connecting the T5V to either pin 10 or pin 12 turns on the power supply, but I'm afraid to try without knowing more. I've got to find out what the trick is to turn on the display before I can move forward.

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