I've done battle with many Miprom 21's with the Allen Bradley drives, and when they start blowing semi conductor fuses, its never good. You could start throwing drive boards at it and be into Kone Spares for the price of a brand new drive pretty quick. I highly reccomend Access Electronics. They've done 2 miprom 21 drives and a kcm 831 drive for me. Their prices are fair and haven't had a problem with their work.