can I access for JEE MAIM without 12th pass and based on diploma ?

Here are the list of qualifying exams below.
List of Qualifying Examinations (QE)
i. The final examination of the 10+2 system, conducted by any recognized central/ State Board, such as Central Board of Secondary Education, New Delhi; Council for the Indian School Certificate Examinations, New Delhi; etc.
ii. Intermediate or two-year Pre-University examination conducted by a recognized Board/ University.
iii.Final examination of the two-year course of the Joint Services Wing of the National Defense Academy
iv. Senior Secondary School Examination conducted by the National Institute of Open Schooling with a minimum of five subjects.
v. Any Public School/ Board/ University examination in India or in any foreign country recognized as equivalent to the 10+2 system by the Association of Indian Universities (AIU).
vi. Higher Secondary Certificate Vocational Examination. vii. A Diploma recognized by AICTE or a State board of technical education of at least 3 year duration. [Only for Admission to IITs]
viii. General Certificate Education (GCE) examination (London/Cambridge/Sri Lanka) at the Advanced (A) level. [Only for Admission to IITs]
So as you have a diploma you can give JEE main exam but you can only get admission into IITs through that.