Assuming that no wires have been cut/disconnected and with the power off/removed, measure the resistance (use the lowest resistance setting on your multi-meter) between 0V on the transformer secondary and the designated ZERO VOLT REFERENCE point. It should measure 0R (ZERO Ohms). If it measures zero Ohms, power on and measure the AC & DC voltages between both points. Again, you're looking for a ZERO - 0V (ZERO Volts). Anything other than ZERO (allowing for meter inaccuracies) indicates an unknown fault. View attachment 1002331 View attachment 1032069 Good Luck!