this page has some details on testing the thyristor:
and a great verview PDF here: http://www.jawamoped.com/JawaMoped_Electrics_-_ignition.pdf - if nothing else read this one.
and common issues here: https://www.mopedarmy.com/wiki/Jawa_ignition_testing
the DIY instructions to build one are here:
I have done that twice and it goes from a weak little zap to fucking inch long lightning bolts.
Glad it works but theyre notoriously problematic and I still support Franks suggestion of replacing it when you can. Do read that PDF if nothing else.