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Solved. Q502 was missing.

Q501???

Nice find.

Reminds me why carefully inspecting the whole board under magnification is so important.?

On Apr 1, 2025, 11:28 -0700, Martin via groups.io <mail.martin.thoma@...>, wrote:

Yes you’re right. It’s a typo. I meant Q501. I was checking the schematic to check where to look for a fault on the board. I realized that there might be an inconsistency between schematic and silkscreen. I couldn’t find Q516 (from the schematic)on the board. I think it’s labeled there as Q12. Just for now I took the mosfet from ptt for Q501.

Reminds me that an automated comparison of board images taken after assembly should be able to catch this sort of fault before it gets shipped thousands of miles around the world.? You can even see the dimples in the solder paste where the transistor didn't stick.

Or actually not! It looks as if the transistor had been in place and fallen off. When this did happen cannot be said. It even would have been possible to pass a function test.?
I’m happy that it was possible to fix it easily. This even makes building the kit more fun. The next days I will run further tests to see what I might have done wrong. But I really love the stacked design and the great debugging utility. It’s a great piece of tec! Love it!