I successfully managed to modify the M18x 330W power supply to work in the M17x, which allows for running the M17x with a fast processor and SLI / crossfire. [Update: some people are having issues with the 330W PS running a 920XM processor with 7970m CrossfireX. This combination draws more than than 330W in the M17xR2 for some reason. I have an 840QM and 6990m CrossfireX with no issues, about 200W average] The modification is easier if you already have a 240W power supply, since you will already have the DS2502 1-wire EPROM that is required for the mod. If you don’t have a 240W supply you can also order a DS2502 and program it manually with the 1-wire programmer I posted here. The first step is disassembling both power supplies to get access to the 1-wire memory. You will need a tamper-resistant T10 bit to get the cases open. Of course you will void any warranties at this point as well. If the power supply has been recently plugged in, there is a large capacitor inside that will bite you. As with all of my projects here if you hurt yourself, others, your computer, etc. I don’t claim any responsibility.
The chip you are looking for is in a SOT-23 package. On my 240W supply, the DS2502 was labelled U208.
On the 330W power supply the memory is a DS2501 in a TO-92 package, identifier IC134. Either desolder or cut the leads of the device, it needs to be removed or it will cause a bus error since the master uses a skip ROM command to interrogate the supply. Then solder the DS2502 to the 300W PCB, in the location for IC133.
At this point there are a still a couple more things to do. Unlike the 240W power supply where the ROM is passively powered, the 330W power supply actively powers the ROM; however it is pulled high with too strong of a pull-up for the M17x to reliably interrogate the device. In the active powered configuration the master can’t pull the line low. The motherboard bus master already has a pull-up so it’s redundant anyway. To convert the 330W supply to a passive configuration you need to cut the ID signal trace after it connects to the series current limiting resistor R141. This is easiest between R141 and the via that then goes to the pull-up. The other side of the series resistor goes to the device and together with the zener diode next to the chip prevents in-circuit programming of the device. In the picture you can see I cut the trace just below and to the right of the device.
You will also need to add a jumper wire to the third terminal which for some reason is left floating on the PCB. This terminal needs to be connected to ground. Without both grounds connected the device doesn’t work.
At this point you should be able to wrap it back up. Try going into the BIOS and make sure that “240″ is displayed for adapter rating. You should not get any “non-Dell” messages. OSD may give you an “unsupported adapter” error the first time you load into Windows with the adapter, it should go away after you reboot.
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