[Adamki2000]

This is a different kind of motherboard upgrading question than any of the others I've been able to find on the 'net and I'm wondering if anyone's ever attempted this before and how successful it may be. I have a slot-loading iMac G3 350MHz machine that I want to upgrade since I don't really have the money to go out and buy a new computer and probably won't be able to for the next year or so at the minimum.

I recently purchased the motherboard pulled from a 600MHz iMac G3 and I was hoping I could figure out how to install it into my machine with no problems. I know that it's not quite as simple as "swap out the old and in with the new" kind of thing but what I really need to know is are there any kind of possible hardware incompatibilities I should be aware of before I try to install this new logic board? The down converter (power board) I think was the same across the entire 350-700MHz iMac line. However, I know there were 2 kinds of CRTs used and therefore 2 analog/video/power boards as well. I know my iMac right now has the LG CRT display and the corresponding PAV board (with the switch for either an LG or CPT CRT). The question is, if I plug the down converter board onto the iMac 600MHz logic board, attach it to my current PAV board and try to power it up, will it work? I'm afriad of blowing out a board or making the CRT explode or something. I doubt it'd be that bad but should all the parts of the iMac 350 be compatible with the newer logic board?

I'd think the answer would theoretically be yes but I don't know. So far I do know that my heat shield had to have the cutout on the back for the VGA port sawed out so it'd fit around the 600MHz logic board and I know that I'm going to have to move the heat sink on the divider panel down just a bit and apply a thermal pad to keep the 600MHz processor from overheating but aside from that, do you guys know if that's all I need to do? No parts of my iMac 350 need to be replaced with newer components from a 600-700MHz iMac?

Thanks for all the help!

[Detrius]

The only thing you need to worry about is the processor heatsink. As long as the metal that comes up from the machine's frame is in the same location, you are fine. That's all you need to worry about. Everything else is compatible.

You have to match the PAV board up with the CRT.

[Adamki2000]

Oh thank you, thank you, THANK YOU!!!! I was hoping that was all that was needed and that the PAV board would be compatible. Looks like that's the case and I already took care of moving the heatsink down a bit on the divider panel and it's now mounted in it's new position, with fresh thermal pads in place. Now to reassemble it and let you guys know if all goes well as planned! Again, thanks so much for that much-needed information! :-D

[Adamki2000]

Ok, well I reassembled my iMac 350 with the 600MHz motherboard and booted it up and all seems fine for the most part. For some reason, my ethernet port doesn't show up in the network configurations part of the Network pref. pane. I haven't tested whether the FW ports work because I don't have a FW device but when I get a chance I'll test them. The ethernet port is a priority because I'm at college and obviously we connect to the campus network using ethernet. The other odd thing is that the power light on the front of the iMac now stays a solid (if slightly dim) orange instead of the green color it was before the upgrade. As far as the procesor heatsink, I moved the metallic piece that was on my divider board down and over about an inch and I had to wedge some aluminum foil underneath it in order to raise it to the level it needed to be at in order to make contact with the processor. Of course I remembered to apply a thermal pad to the processor too. I'm wondering if that was enough though because after about 20 minutes of use, and a couple restarts to try and see if I could get OS X or OS 9 to recognize my ethernet port, the computer froze midway through rebooting and I had to hold down the power button on the front of it to shut it down. I'm wondering if it froze up because the processor might have started to overheat? I shut it down for a little while and will try booting it up again later but if anyone can help suggest why these things may be happening I'd appreciate it once again. I'm wondering if my PAV board from my iMac 350 is providing enough power to the new logic board but don't know if that's a possible cause...

[Detrius]

You shouldn't be having power issues.

It's possible the heatsink isn't making proper contact, as the two were designed differently. I haven't tried doing a permanent mod.

As far as the ethernet port, you swapped out the logic board, so the software is still looking for the old one. This is common with Airport cards. You have to hit Apply in the network pane before it will work. 10.3 is weird like that.

As far as OS 9, if you don't have the latest version of 9, you may not have drivers for the ethernet port.

That's my first theory.

[Adamki2000]

Detrius--Thanks so much for all your help, I couldn't have done all of this without you! I'm an Apple Tech in training and have done many repairs and upgrades and stuff myself so I'm pretty knowledgable but since this is a hack, most Apple resources are no help with this kind of troubleshooting.

I took the computer apart last night to see if I could spot anything out of the ordinary that might have been causing problems and while there's no visible indications of anything wrong, I took the logic board out and will have to wait on replacing it because I don't have any more thermal pads. I'll have to run out and get some later today.

Oh, speaking of thermal stuff, the tech. manuals say to use a thermal pad but could I use a thermal grease like Arctic Silver 5 or something like that or do I have to use thermal pads? It's just that thermal pads are almost at the bottom rung of the thermal ladder and I know I can't use a thermal epoxy because they're pretty much permanent but I was thinking about trying Artic Silver. Also, because I used the heatsink from the 350, it has this black, almost rubbery stuff coating the contact area and after I diassembled the iMac once again I saw that the thermal pad melted onto it and made a mess that was a pain in the ass to clean off. I wound up having to scrape the whole contact are of the heatsinbk off (including the black stuff) to clean it all off. The problem is that the metallic surface underneath is minorly scratched up and I'm not sure if that's going to cause major problems when I apply a new thermal pad (or grease)? Any thoughts on these issues?

Yeah, I don't know what is up with the power button LED issue but I'll see if maybe the cable to it is loose or something. I figured it mayjust be the result of the new logic board because I also noticed that when it sleeps, the pulsating is much slower and gradual than before. I think the FW ports are probably fine but the network issue is the only thing at the moment that has me concerned. I hear what you're saying about having to click "Apply" in the Network prefs. to get the network port to be recognized but what I'm saying is that while System Profiler seems to recognize the ethernet bus, when I plug in my ethernet cable, the Network pane doesn't even list "Built-in Ethernet" as an available port in "Network Status". It lists the modem fine and Ethernet is checked in
"Network Port Configurations" and unchecking and rechecking that and clicking "Apply" doesn't seem to make any difference. Do you think an OS X reinstall may do the trick or can you clarify your earlier suggestion a bit better?

The only remaining issue I have with my iMac is an issue that has nothing to do with this logic board upgrade as I was experiencing this well before I started this whole thing but I'm having major problems with my DVD drive. I have a 6x SR-8185 DVD drive (yes I said SR-8185 and not the SR-8186) and because the 8185 was originally a PC slot-load drive, the firmware updates for it are in PC format only. I wanted to try to make it a region-free drive and last semester I disassembled the drive to clean it and to try to hook it up to my friend's PC to see if he could flash the firmware for me. Well, he couldn't do it because I guess I bought the wrong connector for it and his PC wasn't recognizing it but anyway, when I reassembled it and put it back in my iMac, it wouldn't work. I'd put in a CD and it'd spit it right back out. I've disassembled and reassembled the drive about a dozen times now and I'm fairly confident that everything is where it should be inside it but it still spits CD's back out at me. Last night I figured out that there was one part out of alignment and I put that back into place but when I tried it out and inserted a CD, it made a really loud noise when it was trying to spin up the disc and then it just spit it out and said the disc was unrecognizable. The iMac recognizes the DVD drive when it's connected so I think it's a mechnaical problem and I have been desperately searching the internet for a take apart guide for these slot-load optical drives in the iMacs but haven't had any success at all. Do you know where I could find a manual for taking apart and reassembling these drives to make sure I'm doing it right? If not, it's ok, I'll either eventually figure it out or have to just plunk down $60 on ebay to get a replacement but I'd like to fix this one if possible.

Thanks for all your help and if you'd rather talk with me on AIM or iChat, my AIM sn is Adamki2000. Hope you don't mind but I added yours to my buddy list! Ok, take care and hopefully I'll hear back from you soon!

[Adamki2000]

Ok, well a couple updates--one good, the other not so good. First, the good news is that I was able to repair the mechanical problem with my DVD drive and it's working just fine once again! :-D

The not-so-good news is that there's definitely something wrong with the new 600MHz logic board. I'm not sure what caused it but like I said, I used it successfully for about 15 or 20 minutes with no real problems but after a 3rd or 4th restart, it froze midway through booting up and I was forced to hold down the front power button to shut it down. I then took it out of my iMac to inspect it and when I reassembled it to try booting up with it again, i think I may have accidentally put the logic board battery in backwards and when I tried to boot up, I only heard a faint rapid clicking sound coming from either the back of the computer or the logic board (I wasn't able to pinpoint it). The monitor didn't turn on at all when I tried this and there was no other sound or anything coming from any other part of the computer. However, the clicking sound continued at a steady, even rate until I would hold down the power button and shut it down. Puzzled, I tried booting it up like that again 2 more times but the same results each time. The reason I say that I'm not sure if the bttery was in backwards is because I honestly don't remember if it was when I disassembed the computer again after that. However, I seem to think that I did put it in backwards.

Well, since then, I let it rest a day or two while I went out and got more thermal pads and yesterday when I had all the necessary supplies, I readied the logic board again (this time with the battery correctly oriented) and tried booting it up. The weird thing is that I had slightly more success booting it up this time than the time before it--meaning that I can get the LED to light up upon pressing it, and I hear the monitor come on like it's receiving power (but no image pops up on it at all), but I still hear a few of those weird clicking sounds before the computer will automatically shut down. Repeated attempts at boot up produce these same results each time. I've tried replacing the logic board battery and resetting the PMU a few times but still nothing. Does this sound like a symptom that the processor may be fried or that the logic board is screwed up because I may have put the battery in backwards? Thanks for any help anyone can give me! I hope this logic board isn't truly dead!

[Adamki2000]

No helpful comments or suggestions on this situation from anyone? DetriusI--can you help me out again man?? Thanks!

[Detrius]

Locating the click would be useful, but it could be extremely difficult to distinguish between the PAV board and the logic board due to their proximity. As far as reviving it, I'm no miracle worker. I'm just an experienced bench technician. Once the boards were swapped, you were on your own.

As far as the optical drive, the laser may be out of alignment. In theory, this should be fixable, but I don't know how it would be done--and it wouldn't be done by hand.

[Adamki2000]

DetriusI--Thanks for the reply!

Well, I know that the PAV board and all other parts besides the logic board are fine because I put my old 350MHz iMac logic board back in and I've been using the iMac fine ever since. The DVD drive seems to be fully repaired and to be honest, I'm not sure where the mechanical problem was but I'm thinking it may have been a spring that was a little too loose that I tightened up a bit. So, really the only thing left is to figure out where on the 600MHz logic board the problem lies and then see what can be done once it's been pinpointed. Just curious but is it possible to remove the large square metal heat spreader that's on top of the 600MHz logic board's processors? If I could see the actual CPU chip underneath it, I might be able to get a better idea of if the processor truly is fried but it looks like the spreader is glued on on something.