DNZ15

Hi, I am using a R820T2 DVB-T SDR (USB dongle from NooElec) and was wondering how I can measure the oscillation frequency (crystal) on the PCB. I've hooked up an oscilloscope. Ran an FM receiver program using Gnu Radio. Then I connected the probe of the oscilloscope to the XTALO and connected ground. However the program stops running when I measure and don't get any value. Any suggestions would be great!