The PV150’s positive lead has a black section half way down, which contains a sealed 15A fuse and it’s likely that this fuse has blown due to connecting to a system with an output of greater than 15A (usually connected to two strings at a time, or more than one fuse is closed at once in a combiner box). Voltage is still displayed as a safety feature to show the system is still live. There is a separate link in the black section that measures voltage. Only solution is to buy a new positive lead as the internal fuse is not replaceable (part number 388A688).
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