Thanks Steve. I've been told that there may be a problem with the start up circuitry of some of these APS- SL's. It seems after being in service for a period of a few years if they suffer an external power failure they may not come back when power is restored. They require someone to physically switch them off and on a few times. (this can be a problem if the nearest pair of hand is 50 miles away) However that is not official and I would like to verify or dismiss it if possible. We have a lot of Sl's out there and with Tadiran supporting spares production only from 2007 onwards, my fear is they will not be so readily available. Thanks again for your time Steve...63.