PVM 20m4e ext sync problem


Previously A04_msh.
Hi guys,
After changing some settings I have this problem: if I power on the monitor, without the AES powered on, the screen goes black and the tally light is lit red. The same thing happens if I turn off the AES while the monitor is on.
It all works fine if Ext sync button is pressed after the AES is turned on. Before I turn off the monitor I have to turn Ext sync off and then turn off the AES. Any clues what setting I changed? The monitor and screen is in great shape otherwise. Thanks