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GARMIN GPS 25 / 35 Date Error


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In October - November 2014 three users of our STVASTRO, GPSBOXSPRITE and GPSBOXSPRITE2 units reported the same error in which the date displayed by the video overlay was incorrect. Apart from the date, all the other information displayed, position, time and altitude was apparently correct. Thanks to user Jose Madiedo this problem was rapidly diagnosed as a fault in the Garmin GPS-35 receiver antenna units used with his STVASTRO units. It was found that this problem could be cleared by reseting the device using the Garmin sensor configuration utility SNSRCFG. Thanks to Garmin technical support the procedure for performing this reset is given below.

The date problem is caused by the non-volatile memory of the Garmin GPS receiver and is related to the GPS 1024 week rollover error. It is nothing to do with the STVASTRO or GPSBOXSPRITE video overlay electronics so we cannot provide a general guaranteed fix to everyone who may have this type of problem. If you have any questions about any of the information presented on this page please contact us directly sales@pic-osd.com. If you have questions about the nature of the error please contact Garmin technical support via the Garmin website.

The current version of the GPSBOXSPRITE2-U is not affected as it uses a different GPS receiver.

Image taken on 29/10/14 showing incorrect date of 15/03/95

The incorrect date problem affects the Garmin GPS-35 combined antenna receiver and the Garmin GPS-25 receiver module. Both of these receivers use the same chipset. It is believed that the error occurs due to an incorrect setting in the non-volatile memory of the receiver after a GPS euphemeris update related to the 1024 week rollover. The GPS-35 is used with the STVASTRO unit we sold from 2001. The GPS-25 was included in the GPSBOXSPRITE and GPSBOXSPRITE2 units we sold from between 2009 and 2011. Users with the GPS-35 can apply the reset fix below via SNSRCFG from a PC directly.

GPS35 with STVASTRO

GPSBOXSPRITE

GPSBOXSRITE2

If you have a GPSBOXSPRITE or GPSBOXSPRITE2 with the date error you cannot use the SNSRCFG fix as the Garmin GPS-25 receiver in these units does not have it's RS232 receive line connected externally. It therefore cannot communicate with the SNSRCFG program. The internal GPS-25 receive line is connected to the microcontroller in these units so that in the event of the receiver losing it's application specific setup it could be reset. However this problem with the GPS-25's non-volatile memory cannot be cleared with the programmed reset procedure.

There is no way to change this without taking the unit apart and either using a connector for the GPS-25 or rewiring the GPS-25 to the existing external connector. Neither of these options can be done simply by the user. Although any competent electronics hobbyist could do the required work, it is slightly complicated by the tight space inside the unit. Details of the change which needs to be made are given below. If you are able you may make this change yourself or have the change done locally by a competent person. Based on the experiance of some users the problem can reoccur. We have not diagnosed this fault or studied its origins ourselves. Therefore we cannot guarantee that this fix will work in all cases. Also we cannot guarantee that this error will never happen again or that there may not be some other fault either unknown or undetected that may show up in the future.

Owners of the most recent GPSBOXSPRITE2-U units are not affected as these units do not use the Garmin receivers.

Garmin GPS Receiver Reset Procedure

The following procedure was sent to us by Garmin technical support. It is for for the GPS25-HVS, but this is the same chipset as the Garmin GPS-35 and has been shown to work with that device. As it was for the GPS-25 they advised that the antenna be removed. You will not be able to do this for the GPS-35 as the receiver and antenna are a single unit.
First you need to download the Garmin configuration software SNSRCFG and set it up on a PC with a serial port you can use to connect to the GPS. If using with the GPS-25 remove the antenna from the receiver.
 
1 Run SNSRCFG (or SNSRXCFG), choose the appropriate model of GPS receiver and click OK
2 Use Comm/Setup, choose the correct com port, choose Auto for baud rate and click OK
3 Use Config/Switch to NMEA mode and click through the pop-ups
4 Use Comm/Connect (must be successful in order to continue, but a connection at a baud rate of 38400 or higher indicates a wiring error)
5 Use Config/Get Configuration from GPS ( This step is critical. If missed the receiver may no longer send the correct data to the video overlay )
6 Use Config/Sensor Configuration, make sure that Phase Output Data is not checked (this is called Garmin Binary Output when running SNSRXCFG), make any other desired changes and click OK
7 Use Config/NMEA Sentence Selections, select the desired sentences and click OK ( Skip this step if only the date is being reset )
8 Use Config/Send Configuration to GPS
9 Use Config/Sensor Configuration and click the Reset NonVol or Erase NonVol button, whichever of these is present on the version of configuration software you are running
10 Cycle power to the GPS receiver, re-perform steps 1 through 4 and then proceed with step 11
11 Use View/NMEA Transmitted Sentences and see what date is coming from the GPS receiver. If it is still 1024 weeks behind, then follow steps 12 through 16. (Otherwise, you're done.)
12 Set your computer's clock ahead 9 years
13 Use Config/Get Configuration from GPS
14 Use Config/Send Configuration to GPS
15 Repeat steps 12 through 14 two more times
16 Cycle power to the GPS receiver, set your computer's clock to the correct date and time, re-perform steps 1 through 4 and proceed with step 17
17 Use Config/Get Configuration from GPS
18 Use Config/Send Configuration to GPS

GPSBOXSPRITE2 GARMIN GPS-25 Connection

In order for the reset procedure above to be used with the GPSBOXSPRITE2 units the following change needs to be made. The internal GPS-25 connector, below left, needs to be rewired so the serial input line is disconnected from the board and connected to the external GPS out serial connector, below right.



The GPS serial in pin on the GPS serial out connector is shown below left. It will be unconnected as shown. The wire that you will find connected between the GPS-25 serial input and the board will not reach this pin. Therefore a short length of wire needs to be connected to this pin which can then be spliced with the wire you disconnect from the board. The GPSBOXSPRITE2 is shown. In the GPSBOXSPRITE unit the serial out connector is a female DB9. The connection should be made to pin 3 of this connector.


The wire from pin 5 of the GPS-25, grey in this example, is the serial in connection to the GPS receiver. It is connected to the video overlay board as shown below right. This wire must be cut at the board end. It should then be spliced with the wire added to the serial in pin of the serial out connector. This will then allow the serial cable sold with the unit to connect a PC to the internal GPS-25.

 
 

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