This board is out of an appliance test station (Clare A433). The unit tests the earth circuit, insulation resistance, load current and also has a HV flash probe to check for flashover from live parts to metal casings. The insulation resistance function is faulty - it’s meant to apply 1 kV ac between L+N and E (ground) and measure the leakage. I’ve narrowed the problem down to this board:UIKEYINPUTRIGHTARROW The component PD1 is open circuit. Here are some details of the numbers, but they are hard to read: Is PD1 a power diode? Do the (obscure) numbers ring a bell? The best I can make out is CP2060A. Many thanks.