Is my hitachi 46f500 projection tv ready for switch to digital

You need to disable SAP function is located on the remote of your set.

Yes - You have to put the TV in DCAM mode. Goto www.TvRepairKits.com - on their tips page they have directions for running DCAM.

on/off sensor/switch went out

If this problem has been gradually getting worse, it is most likely to your picture tubes getting weak, and it is time to replace the set I'm afraid.
If the red is smearing off to the side of reddish objects in the picture it is most definately the tubes.

I just had the convergence replaced and have a great picture

This TV will need a converter box. It was made in the days before the digital tuner was required on big TV sets.

Just remember the converter is only needed if you get off-the-air reception with an antenna for local channels. If you have cable or satellite and get your local channels that way, you don't have to do anything. The change to digital will not affect you.

If you are now using rabbit ears or an old worn-out outside antenna, you might think about upgrading your antenna when you get a converter box. Signal strength is very important with the new digital broadcasting. Too weak a signal means no picture at all or one that freezes up or turns blocky. The antenna that worked for analog may not be adequate for digital.

You can find a new Hitachi replacement protective screen and screen assembly for a model # 46F500 from a major Hitachi distributor at the following links:

Hitachi 46F500 Replacement Part Screen Assembly

Hitachi 46F500 Replacement Part Protective Screen / Ultra Shield

You Dont need one your set is HD. So when the switch happens you are good to go. The only TVs that are going to need converter boxes is those who do not have HD or only have antenna.

It is my understanding that the 46F500 HD Ready only goes to 1080i and for Blu Ray you need 1080p. There are no ports for this format.

replace convergence amp ic
http://home.earthlink.net/~oleg.filippov/ConvergenceFix.htm
http://cmpalmer.blogspot.com/2006/11/fixing-my-own-tv-part-ii.html