I am using an AD9958 frequency generator on its evaluation board and tried to replace the external frequency reference signal (25MHz) with an onboard crystal (25MHz). Following the sketch in the guidance I soldered this crystal ABLS-25.000MHZ-B2F-T - ABRACON - QUARZ,25M, 18PF CL, HC49/4HSMX | Farnell Deutschland onto connector X2 and 0Ohm resistors to R52 and R53. Onto positions C66 and C67 I soldered first 33pF capacitors and later additional 6.8pF in parallel (which is reasonable close to the demanded 39pF).
Finally I soldered 0Ohm resistors to positions R44-R49 and set jumper W11 ("clock mode select") onto crystal.
While the DDS worked fine with the external reference source, it does not if W11 is set to crystal. The clock signal is monitored on J13 ("SYNC CLK").
What am I doing wrong? Do I have to get rid of the C21 and C21 capacitors to get the crystal to work?