Hans

I have no experience to comment on that. Why is the 1 MHz clock speed of importance to you? Btw, the github version of Attinycore supports more clock speeds between...

You could try to use one of the working ones for attempting to burn the bootloader on one of the defective boards.

You need [LGTISP](https://github.com/SuperUserNameMan/LGTISP) to burn the bootloader via SWD and SWC.

There is a LarduinoISP sketch amongst the examples. Did you compile and load that one? It also mentions how to wire it up. You need to look at the right...

This is the example I mean. It comes with this core. 

LGT as ISP has these connections.  If that does not work, I will dig up my LGT's and hook them up. Has been a few years since I had...

Well.... you are posting your question in the Github forum of the core I am using, so I assumed you will have the LarduinoISP as well. But apparently not Here...

That's the one I use.

I honestly have no clue. Here is the LarduinoISP sketch ``` // 20 July 2020 David Buezas // - Bundled and added menu utility // * When uploading to the...

LGTISP.ino may be a newer or older version. I have not used it myself as I usually grab my dedicated SWDICE programmer. The sketch I just uploaded here I have...