Here we go..another iMac G3 Rebuild Thread!

[ultmtfloydian]

Alright, so I know this project has been attempted many times by many different people..some successfully at that I've always loved the G3 iMacs more or less due to their uniqueness, nostalgia, and of course, those killer colors. Probably my all time favorite computer made. The model I'm looking to do a rebuild on would be a slot loader iMac.

Now the typical way that people have gone about doing this is by removing the CRT tube and naturally the ancient logic board inside. I'm going to be getting a hold of a few of these iMacs soon for the purpose of a rebuild..and maybe a fish tank (we'll see). I've dug around in these machines a lot over the years, but probably not as far as I will have to this time around. My primary question before I get this thing going is (and bear with me) is it 100% necessary to even take the CRT out? Is the monitor unit itself actually built into the logic board itself or fused together somehow? If I recall, the tray loaders actually had an internal display port connected to the caddy/logic board didn't they?

My reasoning for even considering salvaging the internal monitor unit is for the sake of preserving as much of its vintage charm as possible..nothing beats that electrical dong noise those old tubes make when they fire up! To be honest, I have a feeling these units' monitor is somehow fused to the logic board to prevent this sort of thing from being done..not to mention the radiation/health concerns of tinkering with the tube.

Anybody have any thoughts on this endeavour before I start laying the framework down? Oh and pardon me if this happens to be in the wrong category. Doesn't seem to be a terribly specific place to stick this thread unless I missed it.

 

[havokalien]

ifixit dot com. CRT needs no removal to take apart. its seperate from the logic board, the crt power supply is seperate from the logic board also, its capacitors are known to go bad at this age. its a lot like the cube really, shell and trim come off then you can take apart all the innards pretty easy.

 

[MagicBoy]

Depends on the age of the iMac. Early machines (like most CRT all-in-one computers) the logic board and drives etc come out as a single assembly to be worked on away from the CRT in the main chassis. Later iMacs had a trapdoor for the RAM thereby avoiding having taking the entire thing out.

They like to keep consumers away from the CRT itself as a 20kV shock won't do you any good.

 

[0248294]

The CRT's circuitry is separate from the main logicboard of the computer itself. The problem however is that next to the video signal, the computer sends signals to the CRT to wake it up from sleep or at boot. Even though you can feed the display video (in the case of the trayloaders, with the DB-25 video connector, or with the slotloaders by tapping the RGBHV lines in the connectors from the motherboard to the PAV board), it needs to be powered up, and there you'll find little to no information on how that's done. There was a guy who had done this with an eMac G4, but he vanished leaving no documentation of how he did it from what I remember. So unless you're good in backwards-engineering the CRT control system of the iMac G3, you're probably not going to figure out how to do it.

EDIT: Looking back, he was able to feed it a VGA signal while the eMac's logicboard was still attached which made the CRT work. He never figured out how to get those I2C signals to be emulated by something like a PIC controller, and then vanished. So you're kind of out of luck on that.

 

[ultmtfloydian]

The CRT's circuitry is separate from the main logicboard of the computer itself. The problem however is that next to the video signal, the computer sends signals to the CRT to wake it up from sleep or at boot. Even though you can feed the display video (in the case of the trayloaders, with the DB-25 video connector, or with the slotloaders by tapping the RGBHV lines in the connectors from the motherboard to the PAV board), it needs to be powered up, and there you'll find little to no information on how that's done. There was a guy who had done this with an eMac G4, but he vanished leaving no documentation of how he did it from what I remember. So unless you're good in backwards-engineering the CRT control system of the iMac G3, you're probably not going to figure out how to do it.

EDIT: Looking back, he was able to feed it a VGA signal while the eMac's logicboard was still attached which made the CRT work. He never figured out how to get those I2C signals to be emulated by something like a PIC controller, and then vanished. So you're kind of out of luck on that.

Ohh sounds like some Godfather kind of stuff. They'll "disappear" if they find out the secret of the CRT. I figured there was going to be some trickery involved there between the logic board and the monitor itself. Perhaps it may not be worthwhile. Wonder what other options are possible. Maybe even something of the likes of removing the internal CRT and placing an unoriginal CRT monitor inside without its case . Though admittedly that sounds pretty unsafe.

 

[0248294]

The closest you could get is by putting a tiny computer in the case, like the credit card format computers, and put it in a trayloader. With some finagling you could stuff it above the original logic board, making sure to not have the two touch, run VGA from it to the DB-25 connector with an adapter, and solder the side connectors to the credit card computer. And you'd have to find out a way to make the switch turn on the iMac and the credit card computer at the same time. If the iMac has no OS, it will keep the CRT on, but that instead will show the credit card computer's image. The problems with this are that you can't properly turn it off (after turning off the CCC, the iMac will remain on), and you'd have to find out how to get the speakers working with it. A lot of effort that might not be worth it.

 

[ultmtfloydian]

The closest you could get is by putting a tiny computer in the case, like the credit card format computers, and put it in a trayloader. With some finagling you could stuff it above the original logic board, making sure to not have the two touch, run VGA from it to the DB-25 connector with an adapter, and solder the side connectors to the credit card computer. And you'd have to find out a way to make the switch turn on the iMac and the credit card computer at the same time. If the iMac has no OS, it will keep the CRT on, but that instead will show the credit card computer's image. The problems with this are that you can't properly turn it off (after turning off the CCC, the iMac will remain on), and you'd have to find out how to get the speakers working with it. A lot of effort that might not be worth it.

All valid points you are presenting for sure. I debated if this project was indeed worthwhile myself. Just thought it would be a nifty winter project.

After a little bit of though, I came up with an interesting idea..which I'm fairly sure people typically do with these projects; and that's go the Mac mini route. But see, what if that idea is taken a step further. What if instead of a Mac mini, I were to stick in the logic board from a modern iMac? Fiddle around with the power switch assembly to accommodate the differences in cable length/position. Either way, we still run into the CRT issue. But my figuring is I wonder if it would be easier going this route and figuring out how to convert the power signal that's sent from the modern logic board in a way the old tube could understand. It still sounds incredibly challenging but probably still more possible than the put a whole new CRT in. Plus this way, the speaker issue could also be resolved by rerouting the wiring from the modern board to the front facing speakers on the G3 (considering the modern iMacs G5's design and up also have internal speakers). This is assuming that modern iMacs logic board would even fit into the case which I'm not too optimistic on.

On the other hand, if I was to drop a whole new CRT unit in, maybe I could secretly relocate the CRT's power switch to the port area on the side (this could solve the monitor staying on in limbo issue). Seems no matter which route is taken, a primarily preservation route in keeping as much of the original unit together isn't looking too hot. But in the end, maybe that doesn't matter as much. As long as the original "feel" is still there, then the objective goal is still met.

But you have to admit, it's certainly fun to consider the possibilities here

 

[bobesch]

I wouldn't do any changes to the iMac but use it for ScreenSharing / FileSharing in combination with another high-performance machine - maybe the mini as a separate unit close by.
So the winter project will be more on the software than on the hardware side. But will preserve the iMacs soul and a way back to macOS8/9 etc.

PS: hopefully that guy with CRT knowledge didn't vanish because of the 20k volt ...

 

[0248294]

I doubt your iMac logicboard swap is going to work. The only true way to get the CRT to work, is to find out what signals the logicboard sends to the CRT to switch it on, and make a PIC controller emulate this by turning the CRT on when the new computer inside is turned on, and shut it down if the computer is shut down as well. This could very well be possible. I imagine the VGA signals could be used to signal the PIC to turn the CRT on, so that when the PC goes into sleep mode, the PIC turns the CRT off to save energy, and turn it on when the PC is back in business. This is definitely a possibility, but I don't know if you're technical enough to do this. I'm certainly not.

 

[ultmtfloydian]

PS: hopefully that guy with CRT knowledge didn't vanish because of the 20k volt ...

Funniest thing I've read in a while . It's quite probable. Maybe avoiding testing that theory out might be beneficial to my continued existence. But you're right. I believe this is going to be just as much a software project as a hardware project. Maybe some firmware fiddling is in order.
[doublepost=1478684563][/doublepost]

I doubt your iMac logicboard swap is going to work. The only true way to get the CRT to work, is to find out what signals the logicboard sends to the CRT to switch it on, and make a PIC controller emulate this by turning the CRT on when the new computer inside is turned on, and shut it down if the computer is shut down as well. This could very well be possible. I imagine the VGA signals could be used to signal the PIC to turn the CRT on, so that when the PC goes into sleep mode, the PIC turns the CRT off to save energy, and turn it on when the PC is back in business. This is definitely a possibility, but I don't know if you're technical enough to do this. I'm certainly not.

Maybe I may have to concede the CRT preservation of this project. Either that, or have two different iMacs to fiddle with. If I was to give in to a flat screen, I wonder if any company has ever created a curved monitor that unintentionally or intentionally resembles the curve of a CRT. For some reason, having an LCD in a unit designed for a CRT bothers me. It just looks..off. I have two slot loader iMacs in my possession I've had for years, so maybe I'll rip the thing apart to see what I'm getting myself into here (this particular iMac in question won't be the project computer. This machine was my first Mac, so I think I'm going to gut the whole thing just to have the case. Sounds goofy but yeah).

If I can track down the wiring and see what makes these particular things with the CRT ticks, perhaps there's some hope. But I still wonder about the unoriginal CRT unit idea and having the power dip switch somewhere accessible on the outside. Not entirely sure how I would wire the power both the monitor and the logic board itself together from one power cable. Hack job three way splitter hiding on the inside perhaps

 

[bobesch]

Funniest thing I've read in a while . It's quite probable. Maybe avoiding testing that theory out might be beneficial to my continued existence. But you're right. I believe this is going to be just as much a software project as a hardware project. Maybe some firmware fiddling is in order.

I happy with my iMacG3 Graphite to run Tiger, macOS9 or use it just as a kind of fat client to run an additional user-session on any of my intel macs with El Capitan - so it nearly feels like really running El Capitan on that old chap ...
Steering a tiny RasPi-kind of computer box via VNC is also possible but I would be a challenging project when it comes to my knowledge about Linux. With VirtualPC you may even run Win98 or Win2k both with macOS9 and Tiger and speed really compares to my old intel-PC from 1998.
A friend of mine gave me another indigo iMac G3 as a present but unfortunately VNC-equalizer malfunction completely blew away both speakers. So I removed all the inside stuff to use I for ... well, after a year I still don't know for whatever.
I have a lot of respect for the CRT - so I nearly removed everything as a block except from the RAM, Optical drive and HDD. The inner parts are really crammed into a tiny space compared to and beneath the CRT. Dismantling the machine had been really a hassle but I don't want to think about putting everything together again.
The plastic case became also very fragile after such a long time and tend to break.
So I really like to keep the graphite iMac untouched - it's also very nice to see it side by side with my graphite Clamshell both in original and good shape.

 

[ultmtfloydian]

I happy with my iMacG3 Graphite to run Tiger, macOS9 or use it just as a kind of fat client to run an additional user-session on any of my intel macs with El Capitan - so it nearly feels like really running El Capitan on that old chap ...
Steering a tiny RasPi-kind of computer box via VNC is also possible but I would be a challenging project when it comes to my knowledge about Linux. With VirtualPC you may even run Win98 or Win2k both with macOS9 and Tiger and speed really compares to my old intel-PC from 1998.
A friend of mine gave me another indigo iMac G3 as a present but unfortunately VNC-equalizer malfunction completely blew away both speakers. So I removed all the inside stuff to use I for ... well, after a year I still don't know for whatever.
I have a lot of respect for the CRT - so I nearly removed everything as a block except from the RAM, Optical drive and HDD. The inner parts are really crammed into a tiny space compared to and beneath the CRT. Dismantling the machine had been really a hassle but I don't want to think about putting everything together again.
The plastic case became also very fragile after such a long time and tend to break.
So I really like to keep the graphite iMac untouched - it's also very nice to see it side by side with my graphite Clamshell both in original and good shape.

I also have an Indigo iMac which happened to be my first Mac. This was the onexact I tore apart as sad as that makes me, but I suspect the logic board has cooked on it or is in the process of doing so. And when I purchased it off ebay, the monitor has always been dull and blurry even after I adjusted the CRT switches on it. So yes, pulling the thing apart breaks my heart, but my figuring is that maybe this iMac can be the rebuild machine to honor it's legacy..even if it's just a case presently which is still sad.
[doublepost=1478785760][/doublepost]I believe I've tracked down the internal display port on the rebuild machine. It looks proprietary but I'll pull it off and see what it is. Either way, I have an additional graphite iMac standing by for parts and will take the CRT tube out of that one seeing since the CRT in the indigo model that has been selected for the upgrade is dull and blurry. I'll post more info as I dig around further.

 

[ultmtfloydian]

Someone over at tonymacx86 seemed to have a similar idea as I did. This image was him trying to homebrew a cable that converted the video signal from the internal 20 pin proprietary to VGA. Perhaps I could attempt to reproduce this cable he made. Now if I were to get ahold of a non original 15 inch CRT somewhere, perhaps I could take the case off of it and attach it to the center plate. My figuring is that because most CRTs already have the capability to turn themselves off when no signal is present, I could bypass the logic board sending the power signal issue.
[doublepost=1478920405][/doublepost]This is the link from tonymacx86 for credits for the picture: https://www.tonymacx86.com/threads/imac-g3-slot-mod-video-connector.125515/

If I stick a Mac Mini logic board inside and reproduce that cable with an adapter that converts the signal either to HDMI or mini-DVI, perhaps that might do the trick. Very hack job approach at this though in my opinion.

 

[128keaton]

Someone over at tonymacx86 seemed to have a similar idea as I did. This image was him trying to homebrew a cable that converted the video signal from the internal 20 pin proprietary to VGA. Perhaps I could attempt to reproduce this cable he made. Now if I were to get ahold of a non original 15 inch CRT somewhere, perhaps I could take the case off of it and attach it to the center plate. My figuring is that because most CRTs already have the capability to turn themselves off when no signal is present, I could bypass the logic board sending the power signal issue.
[doublepost=1478920405][/doublepost]This is the link from tonymacx86 for credits for the picture: https://www.tonymacx86.com/threads/imac-g3-slot-mod-video-connector.125515/

If I stick a Mac Mini logic board inside and reproduce that cable with an adapter that converts the signal either to HDMI or mini-DVI, perhaps that might do the trick. Very hack job approach at this though in my opinion.

second gen intel Mac Minis can be found for cheap on eBay. Upgrade the CPU and RAM, throw in an SSD, and you'll be in business. Get some SATA extenders and move the CD drive in front of the slot. DVI onboard + USB. Heck, you could even move the headers if you really wanted to.

 

[ultmtfloydian]

I've come across an unfortunate truth which I thought might be an issue. The PSU board itself is partially integrated with the CRT. Foxconn decided to hot glue some of the monitor's connectors straight to the PSU board. This issue might very well be the issue that makes me abandon preserving the original CRT because of course I need to connect a Mac Mini to a PSU. So the route of acquiring a non original CRT seems necessary at this point.

 

[MysticCow]

If I were to junk one of my iMac G3's I'd likely cry.

That being said, I know there will come the highly unfortunate date where this has to happen. Fortunately, I have cats! So the G3's will likely be repurposed as cat beds.

 

[ultmtfloydian]

If I were to junk one of my iMac G3's I'd likely cry.

That being said, I know there will come the highly unfortunate date where this has to happen. Fortunately, I have cats! So the G3's will likely be repurposed as cat beds.

I totally hear you. I hate that I had to do this to my beloved iMacs, but the unfortunate fact is that the logic board in my first Mac which is my indigo iMac was beginning to go and since the day I bought it the monitor has been messed up. I wanted my first Mac to live on with new life (I've literally had to fix that thing 12 times throughout its life, so one final rebuild would let it's legacy live on).

 

[0248294]

I actually bought a dead Indigo to revive. This was when I was crazy into iMac G3s, but more and more I start to notice the major flaws these machines have: Bad CRTs. They just aren't of good quality, so many CRTs of that era still live, yet these are nearly all going bad. I know, there is a reasonably warm G3 machine underneath, but still, they are just weak. The fan-less-ness (that word is a mess, I know) of the slotloaders just adds insult to injury. Both my Bondi and Tangerine trayloaders already exhibit problems, as do my Graphites occasionally. I plan to sell them cheaply as is for another collector who is willing to take their time to fix them. Maybe I'll part the Tangerine, since it's in such bad condition. I will keep the Bondi due to its historical importance, and I'll mess with the Indigo as well. Maybe try and upgrade it to a G4 someday, when I get the soldering equipment and the appropriate 7410 G4 CPU.

 

[havokalien]

The CRT's are not bad. The power supplies are weak normally for the load of the motherboard, drives and CRT. New capacitors on the power supply normally fixes most issues. Still not bad for 15 years old, and the size of the power supply is small.

 

[Cox Orange]

second gen intel Mac Minis can be found for cheap on eBay. Upgrade the CPU and RAM, throw in an SSD, and you'll be in business. Get some SATA extenders and move the CD drive in front of the slot. DVI onboard + USB. Heck, you could even move the headers if you really wanted to.

Or, if he wanna keep it PowerPC, he could use the mainboard of a late ibook G4 or small PowerBook (faster CPU and better GPU than mac mini G4, if one plans to use a G4 mini instead of Intel) or in case of a hackintosh or Win-PC a NUC-like PC could be used.