may be this is a bit off topic here but I bought a 3 year old D-Series lattitude leasing laptop D600 in Ebay. My old notebook had a 2 pin power connector and the switching supply worked down to 12 Volt. Only battery charging was disabled if power supply was not 18 Volt. From this reason I always used a direct 12V supply in my car without step up converter.
I tried to do the same with my D-series Dell and it did not work. First suprise was a 3 pin connector at the well sealed power supply. I found the pins for GND and +18Volts but the appliance switches off at a threshold of of only 17,5 Volt. No chance without step up converter. Therefore I tried a simple switcher from National Semiconductor and I can switch on the Dell with it. After that an error message from the BIOS appears becouse of unknown power source. From this reason I tried to find out the signal of the 3rd pin. No success with ohm meter or meassuring volts at this pin. Therefore I opened the well sealed primary switched power supply with brute force using a saw blade. Luckily I hit only the aluminum heat sink and the power board is still working for further analyses.
The secret of Dells third pin is a custom chip with supsicious similarity to the Dallas DS2401 2 wire silicon serial number. See datasheet at maxim-ic.com. Probably it is a DS2401 with its content factory lasered for Dell. Disassembly of Bios shows that the number is checked to distinguish between 60Watt and 80Watt power supply models. The D800 works only with 80 Watt Power supply and the D600 works with both models.
There are still many open questions an maybe anyone else is able to give some hints:
- what circuit is inside the Li-Io battery pack? 3 cells make 11,2 Volt but there are additional active control pins in use. Even if I have a power supply in parallel the computer switches of after one second when removing the battery pack. In general it must be possible to run the computer directly from 12 Volt source.
- the BIOS is CRC32 secured and flash memory contains a service tag and optional passwords. Dells support is using a tool what can calculate a password from the service tag what resets all user passwords. Anybody already disassembled the Bios or knows more about this feature ?
- the port replicator can power up the laptop with closed display. Anybody found something for the pin assignement of the port replicator? That would be an interesting feature if the notebook is used in the car under the seat (with external monitor and keyboard)