AP 74 not turning on after update of 5.6.1

[lbbailey]

downloaded 5.6.1 to EFIS D100 and all appears to have downloaded properly but the AP74 will not turn on hence no AP.Please advise where to start to find problem. Thankyou Lloyd

 

[dynonsupport]

First question: when you did the firmware upgrade, were all of the devices - AP74 and Servos - powered on?