I was working on this for kicks mainly as I had a dead XBox mobo laying around. I've got two chips soldered onto the bottom of the mobo as well as the standard 64mb it comes with. One of the chips is currently missing a pin as I accidentally broke it (mostly) off during the removal process. I'm going to take a dremel to the casing and see if I can get a wire soldered to it and the appropriate pad (its near the corner of the chip so it should be a piece of cake). So far when I've booted it up it doesn't issue any FRAGing or any behavior indicating something horrific has happened, so far so good. However when I popped in a Duo X2 GS today and booted up with the Cromwell BIOS (one that DEFINITELY supports 128mb of ram added in and not just via a debug box) it only showed 64mb. I must admit I'm not a knowledgable enough hardware hacker/engineer to know how ram is counted up at boot on a standard PC let alone an XBox but I'm guessing it either isn't counting the extra 32mb either because one pin is missing (I checked the datasheet and its function IS duplicated but I'm not 100% sure the pin isn't necessary for the function to still work) or because it needs all four chips soldered in correctly at the same time. I'm guessing its like RIMM needing a terminator or else it won't work but on a chip level? I haven't a clue. Or does the XBox only enumerate 64mb or 128mb? As in nothing in between? Hey I just realized that this topic is better served in the XBox development section. I'd be thrilled if a mod could move it. Pretty please?. On top of that I think there could be potential for Chihiro hacking.
Why don't you post the chip datasheet and the number of the pin that you borked. I'd bet on a soldering issue somehwere. Macro pic of the job?
Did you mount it correctly to the MoBo? How did you desolder from the dead MoBo? You could have damage the chip from heat. I use Chip Quik and I never have any problems.
Yes I made damn sure to mount it correctly as removing it potentially means damaging the working mobo somehow. I could have damaged it from heat but I've no way to test it. I will pull up the datasheet and post a shot of the appropriate page as well as a macro as soon as I'm awake enough to figure out how I get a small hole in my leg that is bleeding a bit.
Sorry guys I can't find my good camera atm. My cell phone does an OK job at macros but I haven't cleaned up the mess the flux left behind so it looks like someone left oil all over the solder pads. I can't *find* any shorts so I'm assuming there aren't any. However I also have no current way to test if the pins are actually connected to the pads beyond my glasses which are scripted to 20/15 vision (I love em). http://pdf1.alldatasheet.com/datasheet-pdf/view/37032/SAMSUNG/K4D263238F-QC50.html The appropriate datasheet. Page 4 has the pinout and without checking the chip itself I'm 99% sure it is pin 79 which is listed as VDDQ. I haven't taken any formal electrical engineering classes nor do I have any books on hand (I'm about 95% self-taught) so aside from their description of: "Isolated power supply and ground for the output buffers to provide improved noise immunity." I haven't much idea what VDDQ is. I'm praying that I can fix the wire by using a dremel to grind off some of the silicon casing and soldering to a bit of the wire inside but I'm not going to bet on it. I'm also hoping that the function is 100% duplicated and nothing of importance is required I've also never heard of Chip Quik. I was using a method I've seen others use where you use desoldering braid to remove as much solder as possible and gently slide a needle between the pins and the pin gently popping them up one by one. I can assure you that it is a less than pleasing method especially with the anxiety it causes. I shall go look into Chip Quik right now. If it'll remove SMD chips as easily as I'm hoping it will It might just solve all of my problems. Then again owning a $500+ rework station would solve my problems as well. Key is doing things on a budget for fun/profit until I can finish my BA.
You can take those chips off in 30 seconds with a aoyue 968. $150 VddQ is an additional power supply pin, it will likely be 3.3v. Even though it may be possible to run the chip without it, it's bad practice.
Good to know and I agree. I plan to see about fixing the wire later today. In the mean time I'm going to go eyeball my DDR sticks for a set of chips that match the specs as closely as possible. I've seen a handful of compatible chip models on the XBox Linux wiki but nothing more than "these 3-4 are known to work as well". Probably could use chips with better timing but I doubt I'd see an improvement at all given half the ram would still be stock.
Funny, I thought they were more in common with video RAM used on OLD GeForce cards (I believe the old GeForce 256), and not so easy to get (even from a vendor).
As far as i can remember, one of the lower level functions of most xbox bios's is a check which sets the highest stable ram speed. As you guess it will drop it to the lowest useable clock of your existing stock ram.
