SR620 error...

[browndav]

I'm calibrating a SR620 counter made by stanford research and am having a problem with it from about 5 Mhz up.  It reads dead on at 10 hz but at 10 Mhz the frequency fluctuates about 200 hz up and down.  Running ACal doesnt help, adjust trigger levels has no effect, we've even tried the 10 Mhz adjustment with no luck since the 10 Mhz signal is so bad.  I'm leaning to a NRTS action but was wondering if anyone else had any ideas about it or new anything more about this counter.