Early Zenith PC Laptop

I recently came across an early Zenith PC laptop, that was not working and the price seemed right (free!). It's a model ZFL 181-92. My web research came up empty as far as a service manual goes, and am wondering if anyone has any leads/pointers to one. Plugging in a 12 vdc adapter does nothing, however if I take out the battery pack (it's a sanyo and the cells do add up to 12v!) and connect my power source there, it comes alive. This leads me to think it's either a bad connection on the connector or some bad components at the power input side. I should be able to figure that out when I open it up, but the thing that has me puzzled is a 'hum' that is directly proportional to the brightness control. Any ideas on what this could be? The other problem it has is a "disk seek failure". I am assuming this is a cleaning and lubrication issue with drive a:? Swapping drives is not an option since they are not stock 3.5" drives... Any ideas would be appreciated Cheers Alex