21st Century Technology Chairman Jan Holmstrom has quit in the latest in a series of board changes this month.The AIM-listed company, which supplies on-board CCTV systems to Arriva and FirstGroup buses, said interim Finance Director Mark Elliott had agreed to act as Executive Chairman as the company starts its hunt for a new Chief Executive following the incumbent boss Wilson Jennings' decision earlier this week to step down. Jennings has agreed to stay on for up to 12 months while the search goes on.Elliott said Holmstrom had told the board he was not able to commit sufficient time to an executive role. 21st Century Technology said it would also be looking for a new Finance Director and another Non-Executive Director. The company said: "Once these appointments have been made, Mark Elliott will revert to the role of Non-Executive Chairman."On Thursday, 21st Century announced that Jamie Cumming was joining the board as Non-Executive Director, replacing David Voss.The boardroom shake up comes hot on the heels of a profit and revenue warning from the company earlier this month which sent the shares tumbling.They were down 7.9% at 5.88p at 09:02 on Friday. TB