Kiwi not booting with GPSDO connected


i have two kiwis here on my bench which are not booting as soon as a LeoBodnar GPSDO is connected to the

ext. clock input. The kiwi and the GPSDO are connected to different isolated 5V power supplys. So there is no groundloop.

When i connect the power to the kiwi, the ethernet port lights up for a short period and goes off and stays off.

The blue lights continue to blink.

When the kiwicape is on an AI, it boots with the GPSDO connected without a problem.

Does anyone has an idea to get it boot on the original BBG?

Thanks, Holger OE9GHV


  • Power quality is the #2 source of problems with Kiwi installations. Go buy a 4A+ 5V SMPS and feed it to the Kiwi and Bodnar together. If the combination works then you know your assumption about your two supplies not having a ground loop (or some other issue) is not correct.

  • hi,

    thanks for you answer, but on the rx site i have a 5V 25A linear power supply to power all kiwis.

    At the moment they are powered from a linear dual channel lab power supply. both channels are isolated. but there is no difference if i connect both to the same cannel.

    I upgraded both kiwis with the newes image. No difference. Also tested two different LeoBodnar GPSDO. No difference. It will not boot.

    Thanks, Holger, OE9GHV

  • edited September 2023

    Does the kiwi boot if the GPSDO is connected but with its clock output disabled?

    It could be RFI to the BBG. You could try to reduce the signal level from the GPSDO. Or add a 50(?) Ohm load across J5 on the kiwi.

  • Yes, If the GPSDO is connected but off it is booting. As soon the kiwi gets a clock signal, it is not booting. 50 ohm load on the kiwi on J5 i have to try.

  • Finally i found the bug. the beagel was booting, but the ethernet port was not coming up when the GPSDO was connected. I found this:

    2. Sometimes the Seeed Studio BeagleBone® Green's network port does not work and must be restarted to resume work. Occasionally this happens.

    Please replace a stable power supply and try again. Usually mobile phone USB power adapter is more stable than that computer USB. Or you can remove the capacitor C162.

    on the website:

    So far i removed the cap from one BBG and now it is working flawless with the GPSDO connected.

    vy 73 de Holger, OE9GHV

  • Is this BBG from an "old" Kiwi? One purchased in the 2016-2018 timeframe?

    There was a run of BBG's that had bad Ethernet PHY chips around that time. They had this ref clock problem but also sometimes shorted internally and self-destructed.

    On the schematic that C162 is a 33pF across the PHY refclk marked "EMI". So they must of had to add it to pass EMI testing. Interestingly however the BBB does not have this. And 33pF is an awfully large value to be placing across a high frequency clock driver like that. So maybe not surprising there are reliability problems when multiple power supplies and external connections in use.

  • i am not shure how old the kiwis are. The S/N was #3112 and #2141. But it is possible the capes where mounted on a different BBG. But it is possible that these are the oldest two BBG we own. All other kiwis boot without an issue with external clock.

    vy 73 de Holger

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