I might be wrong; but I think I’ve got everything covered when I say that there are only three options for a I-Yod verb:
- It says where it is but quiesces – so it’s obvious. (for example יָטַב in imperfect is יִיטַב)
- It disappears:
- like a I-Nun – so look for a dagesh in the second root letter – but this type is quite rare.
- The vowel under the preformative undergoes compensatory lengthening (i.e. it goes to a tsere instead of a hireq)
- It changes into a waw (in stems like Niphal, Hiphil and Hophal)