No chime after turn on and no status LED's
I have a lovely but elderly iMac and it doesn’t get to the chime when you turn it on. With the screen dismantled from the computer the fans turn fully on as expected, and connecting the screen temp sensor quietens them. Voltages on the pins for the PSU appear odd - pin2 and 9 is 3.5V to 3.8V. Pins4, 10, 11, 12, 13 are at 12V and pin 6 is at about 13mV. Non of the logic board status LEDs is illuminated. I can see them but there is no signal from any of them… any thoughts?