X200 with faulty dc power supply on motherboad

[Scottie1971]

Hi all, I have an X200 with a faulty motherboard. When i try to turn on with battery power alone the laptop is dead apart from a low buzzing noise coming from the motherboard which can last from 1sec to a couple of minutes. However when i power on with the adapter and battery in it powers boots up no problem and shows the battery is charging. If i take the adapter out the laptop turns off and i can't turn it on again until i remove the battery and then put the adapter in. I have removed the hdd, fan and RAM from the motherboard and get the same problem. I've also tried a known good battery and also get the same problem. Correct me if i'm wrong but this leads me to believe i've got a problem with a component on the power supply from the battery and since the battery is charging ok that limits the fault to only a couple of components? My problem is i don't have a circuit diagram for the battery supply on the mobo and that my knowledge of laptop mobos is fairly limited. If i could determine the component(s) involved then i'd be confident enough to change it myself so any advice would be greatly appreciated, thanks in advance. Forgot to mention, it's an X200-7459.