Well, you could try the unit with a known good battery ... but it's beginning to sound like the problem could be on the battery charger board (AC Charger Assembly) or the Battery Interconnect board. I would suspect the former (which is, I believe, basically a SMPS). frown

I don't have any of these units to look at (nor indeed, a circuit diagram), Hassan ... but if you have other units available, you may need to do a bit of board swapping now, I reckon.

Maybe someone else on here has recent experience on these defibs (and would like to chime in)? think