I wanted to answer this earlier but I have been out of town for the last couple of weeks for work.
but i think a lot of o2 users it's still thinking:
..if i'll want upgrade my o2 RM5200 cpu board...
-what i must do?
-the mods it's reversible? ...i'll get back the parts changed?
-have you detected "floating point" problems?
-what's the price?
-news from the 900mhz ?
The first thing to do is get an O2 300MHz or 350MHz cpu board. The cpu boards I have upgraded have both been FAB no 034-1451-004 rev A (this is the p/n of the cpu board itself, not the entire cpu board assy with parts) I know there is at least one other rev of this cpu board (it looks slightly different) that I have seen on eBay, I see no reason why it would not work to be upgraded, but I can make no promises.
Contact PMC-Sierra http://www.pmcsierra.com/
and they will put you in contact with your local agent. You will need an RM7000C 600MHz chip, they are about US$140 each + S&H.
Contact me through my e-mail (Nekochan.net members can find this under the "memberlist" link at the top of the page) and I will sell you a preprogrammed PROM chip (for the 600MHz cpu), or you can arrange to send me the cpu board and I will put the chip on for you.
You will need to adjust the core voltage regulator from 2.50V to 1.20V by changing the resisters (R50 and R46) on the cpu board. If you arrange for me to put the PROM chip on the board, I will do this at the same time.
Contact a pcb repair shop and explain to them you have a pcb that you need to replace a "BGA" (ball grid array) cpu chip, you have the chip, and you will expect a guaranty of their work. This should cost about $100 - $175 per board + S&H.
Put the heatsink back on the (new) cpu and you should be ready to go.
you should be able to reverse this mod, but there is a finite number of times you can solder and unsolder from a pcb.
I would ask for the original parts back, ther belong to you.
I have seen no problems at all (floating point or otherwise) from either the 400MHz or 600MHz boards and they have been running pretty much 24/7 since I received and installed them in my O2s.
The samples of the 900MHz chip are going to "big" customers, something about thousands of chips bought per month.
My plan is to document this upgrade process on my website, this is a very busy work time of the year for me so I will do this as quickly as possible.
I am starting on my next project which is to upgrade the R10K 175/195MHz cpu chips to R12K 300MHz chips on the O2 cpu boards. I found a cache of new old stock R12K 300MHz chips for a very good price and this looks like a very "doable" upgrade, I will keep everyone posted.