Howdy Larry.......You didn't mention having a schematic so I'm assuming
you're troubleshooting blind. Do you have any receive audio noise and/or
does the squelch seem to work? If no noise is heard I might start with
injection AF at the volume control to see if you have an audio stage (and
make notes continuously when troubleshoot unless it's a very familiar radio
to you) Does the radio seem to switch from receive to transmit? I'd
probably start by looking at the basic transmit chain for activity starting
with PTT and looking for some low level on a known frequency....say 156.300
(CH6).....of course make sure you're dumping into a suitable dummy load
(good for 25watts at least). Use that fancy scope of yours to look for the
TX chain activity.......It wouldn't surprise me if you had something "like"
a problem with the basic T/R circuitry if you don't have any activity at
all - a typical setup might use a dedicated IC for this purpose. If you
have a schematic.........and could attach it via e-mail I'd be glad to walk
you through some troubleshooting.

Note: Having a second receiver capable of receiving these frequency's
(cheap scanner for example) can make quicker work by finding out whether
you have any low level activity when placed in the vicinity (same room
etc).

73 - Gord VE1AJF