Symptoms of this problem are be-ing unable to power up the Xbox using the power button, Xbox mysteriously being powered on everytime the power plug is in, missing LED colors, eject not working properly.
All these signals are grouped in the vicinity and are the same thin (easily corroded open) track width. They are also all situated around the edge of the board, never seen the corrosion happen in the middle (memory traces etc.), maybe my sample size is just not big enough.
This page has lotsa details on how to probe and determine if you have an open trace.
|Minor Corrosion Fix|
The xbox will randomly turn on if the trace is broken, simply because the input is now left floating ,usually it breaks just after the signal resistor. Why they don't use say an internal pull up (most PICs have this functionality) is beyond me, at least the Xbox won't randomly power on.
Anyways onto the fix itself. You can run a wire straight from the signal resistor to the PIC, or you can choose to patch just the trace that's broken. I chose the later as it wouldn't look so messy. For the minor corrosion, what I did was to carefully remove the solder mask and then tin the traces using flux and solder. For the traces that were already broken, I had no choice but to wire up a patch.
Darkmatter on Llamma.com has this covered really well, however I don't recommend soldering from the tiny vias on the bottom of the board, I've tried it myself and I find it bloody impossible, even with careful scraping to expose fresh copper and some flux, it just wouldn't take the solder. So I opted to solder from the topside (straight from the resistor), fold the wire over the edge of the board and then run it to the next point. Traces A and B are for the Power and Eject (can't remember which is which, some probing will clear this). C & D are the signal wires for the LED colours (Red & Green, again can't remember exactly which is which). Trace E is a power line, if you see any corrosion which will affect any of these traces, patch them as required.
On the right shows the board I did, after soldering the wire in, I then taped and RTV'd (with electronics safe RTV, standard RTV released acetic acid during cure and may cause other problems, maybe you can use a dab of hot glue) the wire to stop it flopping around (and getting caught on something below) and give it some strain relief.
Board now works 100% after the patch, no more random power-ups, non-responsive buttons and having to yank the power cord everytime you want to switch the box off. xD