Make sure your meter isn't burned out. Very unlikely though. Another issue is the FET transistor. I am not familiar with your tester, but I have the B&K 747 and am having issues with getting it to work properly. It seems that several of the meter circuits are much the same in the solid state versions, It could be a bad switch. Very common issue on that point.
Sure is funny about no schematic being found. A lot of B&K products are without any support. You could look in the B&K Web page for support, but I doubt you will get any satisfaction. I have seen schematics from some manual sellers at around $12. Good luck.
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