I don't have an answer for your question, but I find it interesting enough to ask that you post the original "Solution for a dead G 5", as I and others, I am sure, will find it interesting also. Their are many experts here that will know of this "mystery fan" you speak of. Hang in there, many reply's are sure to come.
It's not really hidden, it just sits between the media (drive) bay fan and the side panel so that it isn't obvious.
The blower pushes air down behing the logic board to aid airflow around the chipset coolers.
Those two fans are "part of the case" (2004/early 2005 G5's) as far as Apple service guidelines went. If either failed, the case needed to be replaced.
Keeping all fans clean is always a good idea. They are a pain to clean. Cleaning behind the logic board is a bit involved as well.
Yes, ALL G5's are subject to BGA failures. The memory controller BGA is a common failure in spite of the blower present to push air behind the logic board.
While I was on my search to find this original posting, japamac gets up on the other side of the Pacific Ocean, all bright eyed and bushy tailed, with a fresh cup of Joe, and way more knowledge than me, and beats me with all the info. I stumbled upon, with my lack of skills & knowledge of working / mining this site for bits of info. ..... I bow to the Master !!!
Posted 2:07 am
OK, I found the original Discussion posting and the links for the attached photo's does work, you must rt. click and open in a new page, and their right there. Here is the link for the original discussion ; http://https://discussions.apple.com/message/9024212#9024212 : .... this includes download of tech. pages on the research into the BGA cooling findings. And JeffDy's photo's.
Now I can see (thank you all very much) JeffDy's photos of his filthy fan and other items in his post. And thank you japamac for pointing out the location of this fan. On my G5 I can see that squirrel-cage fan behind the optical drive fan as you said. Japamac refers to "two fans," I think I see one. As for removing them for cleaning that's another matter!
A quick look at my "PowerMac G5 (Late 2005) Service Manual" doesn't seem to mention anything but the media (optical drive) fan. Nor do I see them on the "exploded diagram" of the guts. But I am probably wrong again.
JeffDy's recommendations for improving the seating of the proc or chipset is another issue I may ask about later.
Editorial sidebar: I've fiddled with a variety of PCs over the years but I've always admired the testosterone-rich G5 construction from afar. Now that I have one to learn abt, I think this "simple" dual proc 1.8 must be the most complicated/difficult to work with PC I've encountered. However, they say that "form follows function" and I may well learn to appreciate this beast.
Various ThinkPads with Windows/Linux