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Support Update

Action required for upcoming GPS problem with Week Number Roll Over for GPS units that pre-date 2015

We have been made aware of an issue with the compact white GPS units supplied by us between 2003 and early 2015. During this time, two different chipsets were used in Güralp GPS units, both chipsets were manufactured by Trimble Inc.
•    From 2003, the Trimble Lassen SQ chipset was used.  
•    From mid-2010 the Trimble Lassen iQ chipset was used.

The latest Trimble Product Bulletin explains that these chipsets will both be affected by a WNRO (Week Number Roll Over) event.
•    The Trimble Lassen SQ has an NMEA cut-off date of the 28th July 2019, after which the dates from the GPS unit will not be valid
•    The Trimble Lassen iQ has an NMEA cut-off date of the 29th May 2021 after which the dates from the GPS unit will not be valid (some units may work later than this date but information is currently not clear)

This issue is relevant to Güralp customers using the DM24 and CD24 digitisers or instruments integrated with these digitisers (such as the 3ESPCD, the 6TD and the 40TDE) as they use NMEA.
This is particularly urgent for customers using the Lassen SQ chipset as these will expire on the 28th July, 2019.
This alert does not apply to GPS units purchased since 2015 with serial numbers (visible on the base of the GPS head) starting at G30000 or higher, or, to the new generation black Güralp GNSS Units. The chipsets in these units are from a different supplier and they have assured us that they will have no performance issues.
Our Solution
At this stage we are not offering a firmware fix as there will be no way of testing the firmware release until after the cut off date. Therefore we are recommending that customers undertake one of the following three options:
1.    Purchase a complete new GPS unit
2.    Return the affected GPS units to Güralp for factory fit of the replacement PCB assembly - our usual repair RMA process needs to be followed
3.    Purchase a replacement PCB assembly incorporating a new chipset - this can be manually fitted by the customer - we will provide details guidance on how to do this

We ask that all requests for any of the above options are sent direct to our email address so that we can monitor uptake.
Distributor Service Option
If you purchase Güralp equipment through one of our distributors, they may also be able to office a more local replacement service to you. We have asked our distributors to contact customers regarding this situation, however you may also wish to contact them direct. You can find details of all our current distributors on our website here
How to check if GPS units use Lassen SQ or Lassen IQ chipsets
Any compact white GPS receivers shipped before the 1st of March, 2010 will be Trimble SQ type receivers. Receivers based on Trimble SQ units should be upgraded to avoid problems. Customers with GPS units that were purchased between March 1st 2010 and 2015 with serial numbers that don't start with "G3"  are advised to identify which type of Trimble Lassen GPS chipsets they have. The two chipsets can be visually identified with the top of the casing removed. Detailed instructions on how to do this are in our guidance note.

We ask that all requests for support, or replacement parts/units for this issue are sent through the email address so that we can track demand as effectively as possible.
We are aware that this situation provides some logistical challenges for our customers and we apologise for any inconvenience caused as a result. You may have seen in the media that this situation is not specific to the Trimble GPS chipsets, but is widespread amongst earlier GPS units provided by a number of different manufacturers.

You can read more about the issue in an article on here. (External link)

We will keep our guidance note page as up to date as possible based on the information we receive from the manufacturer and the solutions we can offer to overcome the issues. If you would like to subscribe to hear support updates on this subject please email



For urgent enquiries please call 020 3727 1000 and speak to Fergus Wheeler, Louisa Feltes or Jess Gill. 






Güralp Systems Ltd.( is a leading global provider of sophisticated seismic monitoring solutions used to understand natural seismological events such as earthquakes, aftershocks and volcanos, as well as induced seismic events, or seismic signals, resulting from human activity.

Our solutions are used in research, civil and industrial applications to increase understanding, optimise processes and to protect people and the environment. Our equipment is installed in all major ocean basins and across all continents worldwide.

Our instruments range in performance from very low frequency, very low noise for global seismology to high dynamic range instruments for local, strong motion monitoring. Our sensors and can be supplied for deployment at the surface, in boreholes and on the ocean bottom. We also provide data acquisition equipment, power and communication accessories and data interpretation software.

Our services include installation and commissioning; network operation; repair and maintenance services; data processing and interpretation.

Headquartered in Reading, in the UK, we have been operating for more than 30 years and have established a global network of distributors who provide local customer support and sales services.





Guralp Systems Limited
Midas House
Calleva Park

Tel: +44 118 981 9056
Fax: +44 118 981 9943