Stihl 028 problem.

New to forum.
Purchased a used Stihl 028 AV Super, Electronic Quickstop.
Starts OK, runs great, cuts great.
However, when turning it off, or it dies, it is impossible to restart.
All I hear is a simple 'pop', like a small rock makes when hitting a windshield.
Another owner of a Stihl says it might be an electronic switch or board.
I have no idea.
The last Stihl I owned was an 075 forty years ago. Wish I still had it.
Any help solving this is appreciated.
dlw