OnOff Shim keeps causing reboot


My OnOff shim is working strangely. It powers the PI 3 just fine and when I hold the button for a second it starts a shutdown as expected but after the shutdown the Pi reboots straight away.
I tried a shutdown from the command line and from the GUI menu and in both cases the Pi shutdown and then immediately restarted again.
I reinstalled the software with the curl command a few times but nothing changed. If I take take the OnOff shim off and power the Pi as normal it does shut down so it suggests something about the shim itself is the issue.

I soldered it to the supplied female header so I can take it on and off. The solder looks ok, it all seems to be making contact with the copper and I did re-do the pins but that didn’t fix it.

It does shutdown so the button is registering and the software does cause the shutdown to happen but it seems something is going wrong, maybe with Pin 4, causing the restart. 1-wire is disabled.

How do I troubleshoot this further? Is there something in a config file to check or some way to monitor Pin 4 or check that it is being pulled low at the end. Is it worth powering the shim away from the Pi and checking voltages and what would I check? Can I change the config to use a pin other than pin 4 or 17 to see if other pins work? I have a voltmeter and can supply 5v to the shim away from a Pi if needed.

Any ideas?


Have to ask the obvious question. ;)
Power supply is connected to the shim and not the Pi?


Yep, power to the shim not the Pi directly, but worth asking :)