Dodgy IBM PC Convertible power supply

I've got a couple IBM PC Convertibles that exhibit the same problem with their power supply. When I press the power button (which is a momentary switch) it turns on briefly: the disk drive light goes on and the drive starts to spin or the display shows brief activity, but in either case for only about a tenth of a second. Sometimes if I hold the switch just right I can get it to make it through the entire memory test and up to the point where it wants a disk in the drive, but it's very hit & miss. It certainly is not behaving as it should. I've tried cleaning both the switch and the AC adaptor socket but so far this has not improved anything. The switch seems to be doing its job, and the power seems to be making it to the unit. It just seems like the power supply becomes unhappy at some point, unless I hold the switch in a certain position, but then I invariably lose my touch and the power goes out again. I'm using appropriate adaptors, including a car cigarette lighter adaptor plugged into mains using an AC-to-cigarette lighter socket adapter (kind of handy in this case). I've tried swapping the internal power supplies around between units but get the same problem on each. One has a battery pack and one doesn't, but having it in or not in does not make a difference. Seems like the power supplies are dodgy or something? Any ideas? -- Sellam Ismail Vintage Computer Festival ------------------------------------------------------------------------------ International Man of Intrigue and Danger http://www.vintage.org [ Old computing resources for business || Buy/Sell/Trade Vintage mputers ] [ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]