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Having said that it does sound like the Reg is U/S as well.

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Removed the reg as I was pretty sure thats where the fault was and gave it a shake .
I could hear loose pieces so I pulled it apart and the top of two transistors fell out
plus there was a burn mark where they were, So the printed circuit board is US.
That reg cost $100 with a discount about '94. Brought on on ebay today for $14
for a 20 amp reg mppt

Doesn't the reg have blocking function built in ??