Problem with BG7TBL GPSDO

[DH2FA]

I have a BG7TBL 10MHz GPSDO (pcb version 2018-02-10) which was always on and working fine for about 4 years. A couple weeks ago I noticed that the green LED PWR is off.
I noticed that the red LED ALM comes on for about 6 seconds, then the green LED PWR shortly blinks with the ALM still on. Then both LED are off shortly and it starts again with the red LED ALM.
I checked the 12V supply, it is OK.

I opened up the GPSDP and noticed a blue LED D2 near the antenna connector which also comes on shortly when the red LED ALM starts to light up.
I appreciate any input how to get the GPSDO working again.

There is a little battery next to the TCXO which shows less than 1V instead of 3V nominal. A Google search showed that this battery seems to hold last settings of the satellites for a quick warm start. Could it be the culprit?

[thinkfat]

I think not. You could replace the battery or just remove it entirely, if your use case is "always on". The GPS is not doing any warm starts anyway.

There are only few things that "wear" on a GPSDO. One is the oscillator itself, OCXO's have a limited service life,
Or it could be the antenna or cable. Eventually, moisture will creep in.

Are there no diagnostic outputs that you could use apart from a few LEDs?

[Runco990]

ALWAYS start with the power supply!!!   These little switching plugs are crap and don't last long.  I crack them open and change the bloated capacitors every few years at minimum.  Have been thinking of making a true linear power supply for mine.

[DH2FA]

Thanks for your input. Unfortunately there are no fault messages other than the LEDs.

The 12V wall wart was my first suspect. I used a linear bench power supply with the GPSDO but it didn’t change anything. The GPSDO draws 250mA at start up and after a few minutes it goes down to 120mA. This probably shows that the OCXO has reached its operating temperature.

Unfortunately I can’t find any contact info for BG7TBL. Otherwise I would ask him.

[thinkfat]

Provided all the supply voltages are good, these are the next steps I'd do for diagnosis:

I would start with trying to find a debug UART. Failing that, I would check if the EFC voltage of the OCXO has run towards a limit: then the OCXO is likely end-of-life. In that case - just replace it. Those GPSDOs use surplus OCXOs of unspecified quality anyway.

Next I'd try finding the serial output of the GPS and the 1PPS output. The GPS UART output is likely NMEA and should be easy to decode. This will give you an idea if there's a problem with the antenna.