Nidec is facing renewed investor backlash after disclosing details of quality control misconduct involving motors and other products, compounding the challenges confronting a once-admired manufacturer on top of accounting problems and the exit of its charismatic founder.

Shares in the world¡¯s largest maker of precision motors fell as much as 18% in morning trading in Tokyo on Wednesday ¡ª the steepest decline in six months ¡ª after Kyoto-based Nidec said the issues involved changes made to materials, processes and designs without approval.

What began as a drawn-out scandal caused by a series of bookkeeping errors has now spread to concerns over the integrity of Nidec¡¯s manufacturing? ¡ª built over five decades by its founder Shigenobu Nagamori, who famously said he was willing to ignore investors if he thought they were wrong. With the stock trading at roughly a third of its level five years ago and the chairman¡¯s departure leaving a leadership vacuum, Nidec now appears to face a greater reckoning.