IMO the fact that it won't power up brings this back to the basics of these ski's, not so much thats its a DI. Where the DI's get specific is diagnosing the trouble faults, & air/fuel injection problems. Other than that, they still operate like the rest of them. The fact that it won't power up really shouldn't be that hard to pin down. There is a plug that provides the main power & ground to the MPEM through a 30A fuse in the rear Ebox. from there it goes into the MPEM & is disbursed though multiple fuses directly on the module. on the 2002, the power is there all the time & should be easy to check with a meter, but you need the ski in front of you & a meter. The MPEM is powered up from the DESS post & key. If there is good power & ground, there a good chance the DESS post is bad. Heck, if you can find another shop to diagnose it & they are not to proud to jump on the forum, have them join this thread & we will have this thing figured out.
On a side note, I am trying to remember if the 2000-2002 DI's will power up for 30 seconds from hitting the start/stop switch. MY skis are all still in storage, or I could give you some better & very specific info. I have been through a few skis in the past couple years, so off the top of my head I don't recall what ones have that feature. I know the 2003's & up do not has they have a power cutoff relay controlled from an extra reed switch in the DESS post. 2002 does not have that feature.
While I hate to make assumptions, I would like to believe your current mechanic has properly tested that there is power to the MPEM & all the fuses are good, so good chance its a deeper issue, but again, no power up shouldn't be hard to figure out.
I am thinking the guys here that program keys can confirm if more connections are needed to power up these up besides #24 & #25, but I don't think there is. But again, to try & trouble shoot this without somebody being able to test the suggestions is going to be nearly impossible.
What's your comfort level? Are you a hands on guy, or do you prefer to have a shop do the work? For sure no harm either way, It's always hard to know what somebody is comfortable with, & we sure don't want to talk somebody into doing something that makes them uncomfortable.
I enlarged this diagram so you should be able to open it & zoom in pan/scan & see what is what for connections.
I also circled the DESS connections that are responsible for power up the module if there is power to it. There is a thread from last year where a member had a bad post & no power up. in that thread, there was mention of the correct way to test the post. I will see if I can find it & add it here. This is not everything, but its a place to start.