Thanks Mate,
I've posted on another site and happened to bump into (of all people) an ex-compaq engineer. He says that this is an inherent problem in the Armada range from the 1500 series through to the 1750. Apparently there is a problem with the daughter-board which plugs into motherboard a bit like a riser card. Anyway he says that the whole range of Armadas had been sold before this became an issue and Compaq had a general recall of the whole 1750 range a couple of years ago. I just need to dig up another faulty old armada and half-inch the board from it (obviously one that is not displaying the same problem). Anyway mate thanks for your suggestions. By the way, the engineer says that if I hold down the button which switches the lcd screen off when you close the lid, the display sometimes resets itself.