I've already posted something in the apple support discussion forums but this site seems a little more active and seems to have more people that aren't only on because something broke. http://discussions.apple.com/thread.jspa?threadID=1902823&tstart=15 My June 2004 Dual 1.8 G5 lost a processor in the month of August. Might have had to do with the some 20 fuses poped per week for about 3 weeks (too many people on breaker and all with 3X as much stuff as they should have had). What would happen is it would run for a few minutes, then freeze up and fans rev up, then the grey kernel panic message "your computer must be restarted" would display in 100 languages. I would do a hard reset via the power button. Once started up it would run for any length of time without a problem. I eventually noticed that only 1 processor was displayed in "about this mac" and activity monitor only showed 1 processor bar. I found out that resetting the PRAM would potentially cause the missing processor to come back, so I tried that. After it started up it showed Dual 1.8, but after maybe 45 seconds it had another kernel panic, and of course restarted with only 1 processor. So I tried over and over for a while with no luck and used it as 1 processor. As soon as I could I took it in to an authorized shop. They removed the processors, blew out the dust, switched them around and ran a diagnostic. They told me it was running fine and I could pick it up. As soon as I got it back I started it up and it worked... for a few minutes. After that I could no longer get it to start up at all. My guess is that the defective processor was the lower one and while it was ok to disable it before, the system can not run with only 1 processor in the lower position. Does that sound right? So, I took it back, I went in the back to talk with the guy and we both agreed that we should try finding and removing the defective processor. After that it has been working fine as a single 1.8 for months (except kinda slow). First, it sounds like it really was the processor and my logic board is alright. But would it also be possible that something happened where the 2nd CPU connects and the actual CPU is ok? I don't see any sings of damage or burning on the logic board. I found a 1.8Ghz G5 on ebay (a couple actually) that I think would work. My CPU is a V2 RDU. Does the other processor have to be an RDU as well, or will any NVC, Q79, Q9B, QEH, QJN, QLY, QLZ, QWX, QX4, QYS, QZY, R05, RDT, RDU work? I was looking at a couple web sites that sell parts too and I found that a 2.3Ghz will go for a similar price as a 1.8 on their sites (but ebay is cheaper for the 1.8). The 2.3 is even cheaper than the 2.0. My guess is that there are many many more dual 2.0s out there than 2.3s, and the 2.0 seems to have had reliability issues so maybe the 2.0 is in much higher demand than 2.3s. Does anyone have any experience buying from DV warehouse http://www.dvwarehouse.com? Their parts are a lot cheaper than the new parts shown on other sites. ie, $300 vs $800. I guess they sell refurbished or used parts. But $800 for a processor in a 4 1/2 year old machine is a bit much. I know you cannot stick a 2.0 in a 1.8 machine etc. But my understanding is that the only thing in the whole computer that actually knows what processors should be there is the logic board. So if I replace that with a 2.3's, then my FSB should be 1.15Ghz which matches the processors and there should be no issue. I believe all other components (video card, RAM, ODs and HDDs) are compatible with any G5 from 2003 to early 2005. A bigger question is will it board fit? Since the case is from June 2004, will all the screws and pins on the case be in the right place? Will the little temperature sensor at the front that you are supposed to disconnect when replacing the logic board be compatible with the new board? Will all the fans still be compatible and be sufficient to cool the hotter processors? Also, my computer has a 600W power supply. On parts sites it states that it is compatible with the dual 2.7Ghz (also uses 600W) with the only difference being the older power supply does not have some rubber ring somewhere. Is that part important? Also, the dual 2.3 only used a 450W power supply. Is having a larger power supply going to cause a problem? Does it affect the voltage or power given to the machine? I don't want to fry a logic board because of the wrong power supply. So does it make sense to spend $200 to get the machine back to a dual machine (it really does feel slow)? Does it make sense to spend $1000 on a logic board and 2 processors, then sell mine for about $450 on ebay, making it cost over $550? Or if you think about it a $350 upgrade to go from a dual 1.8 to a dual 2.3 (1Ghz more power). The idea would be to be able to hold off buying a new MacPro at least until the late fall, until these next ones have gone through the teething process, especially with the new OS. And finally, does anyone have some advice for the installation or removal of all the components? The only things I have done before is RAM, graphics, HDs and airport. I have the 2003 G5 service manual (I hope it still applies) and I have an ASD 2.5.8 disk which should work for both dual 1.8s and dual 2.3s. P.S. I'm going to be gone all weekend and have a lot of work to do today so I may not reply right away. Feel free to post away as I'd like all the help I can get so I don't screw things up. Oh and the part numbers I think work would be: 661-3143 for the 2nd 1.8Ghz 661-3587 for the 2 2.3Ghz 661-3584 for the 2.3 logic board And I have looked at 2.5s and 2.7s but the liquid cooling scares me reliability wise.