What could make BLE sample applications not work, but radio works ok?

Question

Hi, got an interesting problem, this is on a custom board with nRF51822 QFAB that we are bringing up. The radio test (not using softdevice) works ok and produces strong transmit signal (as strong or even stronger than from the eval board). However none of the BLE/softdevice examples work. What can cause this? How to troubleshoot? 
 Is there anything different that needs to be done because this is one of the AB (128k) chips? 
 Is there any basic self-test that allows to check that softdevice itself is flashed and working correctly? (correct memory map, calls go to the right functions? etc) This is as opposed to testing that the radio hardware is working ("radio_test_example" ) or that BLE is working ("ble_app_dtm" )

Ole Morten · Accepted Answer

My best guess is the low frequency clock settings. If you try to enable the softdevice, telling it to use an external crystal, if you don't have any external crystal, it will hang. I'd therefore suggest that you try changing the clock source to RC, to see if it helps. 
 This could be worth doing even if you have an external crystal, since there could be something else with the crystal causing trouble. 
 If this is not the problem, it would be very helpful with a little further description than "it doesn't work". :-) (i.e. what exactly happens, have you tried running with the debugger, does it hang, where if so and so on.)