Turned on the amp with D5, R9, and R10 out. It has not dropped into protection after 35 minutes. I did a couple of checks on pins 2 and 4. Pin 2 was at around -3mV after the amp was turned on and at 35 minutes. Pin 4 was at -100mV initially, and fell to about -10mV at the 35 minute mark. Seems to me that pin 4 on the protection board -> pin 23 on the power amp board is giving high values. In the neutral potential adjustment procedure both 3 and 23 should be 0 +/-20mV, and I know I had them down to +/-1mV when I made the adjustments.