No power on my ML SL3 on a stepdown voltage

I need your help.

I have recently moved back to Tanzania with my Martin Logans. The voltage down here is 240V, so I am using a stepdown converter on the Logans, which are 120V. They power-up for about five seconds before shutdown again. Has anybody experience this? Is there a way to by-pass the AC and hook up the needed DC voltage to charge the speakers?

Thanks in advance.

Tasi