I believe that if you have a new enough version of the software (7.2 I think) the series two boxes will all work with the same version of the OS. Just drop it in. If it fails to boot then verify that all the connections are good and try again. If it still fails then the answer is no It won't hurt anything.

One thing that likely won't work is the ability to watch what you recorded on one - on another box - i.e. the stuff on the 140 will not be viewable on the 540.

If dropping the drive in doesn't work then the drive itself will work (unless it got damaged also) but you will likely need to use one of the TiVo upgrade CDs and copy the info from the 540 onto the new drive.

 

I don't think it will work, but it can't hurt anything to try.

 

You will need to re-image the drive with the OS from the 540 box. The OS is different enough to matter.

 

Okay so new question... can I swap the power supply out of the TCD540040 and put it into the TCD240140? Should they be compatible?

There seems to be a guy selling S2 power supplies, and his ad suggests that the one he's selling will work in the 540's and the 240's. Who knows though, given that this is eBay we're talking about...

 

Is this the ebay item in question?
http://cgi.ebay.com/Tivo-Dtivo-Seri...QitemZ110012646902QQihZ001QQcategoryZ79865QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
For what ever it's worth, the pic in the auction is a 240xxx power supply.

For $25, I'd try it out.