kf laser cv joint or transmission ?? How to tell

[lup1]

Thanks, Dirty Hands for your reply.
The c.v joint was replaced 1300 kms ago during a service.
Car rolled to a stop last week, with elderly M. in Law at
wheel.No noise or clunk or crunch, just unable to move.
After 10 minute inspection, emergency mechanics
suggested transmission (4 speed auto) needed replacing. Cost up to $2000. Decided to hold off.
Not been able to get trusted local mechanic to have a look yet but wondering if there is a simple way of working out if it is transmission or cv joint. Reluctant to tackle anything in case it is the faulty new cv joint and then it would be the responsibility of the mechanic who put it in.
Grateful for any ideas.