I had a bunch of mechanical units what I was using to attack an enemy, since they took some damage I sent some SCVs and started fixing them. Instead of getting fixed, they got destroyed. Any ideas why? and how do you fix mechanical units?
To repair a mechanical unit with an SCV, right click on the unit with the SCV selected, or select 'Repair' from the menu on the bottom right. You can also press 'R' then click on the unit you want to repair.
If you accidentally press 'A' then click on a friendly unit, your SCV will start attacking the unit and dealing damage, causing them to explode when they run out of HP.