[Coco] Coco3 appears to be dead: green screen with no text.

[Michael Furman N6IL]

I just received a coco3 that I got on Ebay.  I have connected it to a
monitor with composite video input (not RGB) and when I turn it on I just
see a blank green screen and am not greeted with a ROM copyright info or
OK prompt.  I've looked at the service manual, but have not checked
anything yet.  The fact that the screen shows up at all when power is
applied suggests that the video stuff is okay on the surface.  My
intuition tells me that it is a "Processing problem" (as the
troubleshooting section 6.4 calls it), possibly due to an IC that needs to
be reinserted in its socket.  I can't tell from the service manual or any
pictures on the web which ICs are in sockets and which are not.  I am just
looking for suggestions at this point.

--Mikey