This usually points to the Atmel being unable to communicate with the Si5351a.
Not always the case of the Si itself being faulty.
On the Si5351a board double check the soldering. main things to check:- the 5 volt power supply which feeds the Lm317,the ouput from this should give 3.3v. No voltage here and the Si is unpowered!
Then on to to the 27mhz crystal, and the two bs170's that provide
the level shift to communicate with the Atmel. These form the bulk of what is going on with this board.
Hans does provide a schematic for this which should be easy to follow. Check the two lines coming from the bs170's on the board
with the power off, and see there are connections to the Atmel328 with a DVM for continuity.
If the Bs170's are suspect these would be easier to replace than the Si chip.
I would personally suspect the LM317 first, as any power supply problems to the U3S, the Si5351a hides behind this device, and usually protects The Si from any abuse it may get Hi!
Hope this helps, and i'm sure others will chime in.