RE: DX7 / AR7000 problem (reproducible loss of signal)
I have seen loss of signal from a loose fuse as opposed to a loose battery connection. It took a while to diagnose that problem but it was caused by the pilot shaking/trembling as he flew. He was just excited to be flying and then very nervous when he got glitches :-) The fix was to re-tension the fuse-holder clips
I have not been inside a DX7 so I don't know what the fuse situation is like.
If that was happening you should hear a beep or something if the DX7 beeps with on and off switching?
Just theorising.
Regards,
Eric.