As part of my master's internship, I am going to be using the NanoBrook 90Plus PALS apparatus, which we have in the lab. Unfortunately, it suddenly started giving us some troubles when trying to measure the size of our particles. More precisely:

• After setting up the SOP and starting the new measurement the count rate remains oscillating between 900 and 700 cps (barely reaching 1 kcps for some instants). It is important to note that this happens regardless of the sample that is inside, whether it is the prepared sample or the standard (polystyrene latex standard). It is really strange because just a couple of days ago it was working properly.
• The apparatus is currently operating with the software version 3.5. We tried updating the system but after clicking on that specific button nothing happens (the internet connection was indeed confirmed, we tried both Google chrome and Internet Explorer browsers).
• The diagnostic window helped us obtain for the "Forward Scatter Shutter Open" and "Reference Beam Shutter Open" the values of : 72 kcps and 1652 kcps, respectivly, for "90 Degree Scatter Shutter Open" it remained again oscillating between 900 and 700 cps.

We would really appreciate your support and any insight you could share on this problem and we are open to send any data that could help having a better understanding of the situtation.