Hey,
as in Step 2 described, I tried to measure the voltage at TP22 after plugging the 9V Input at J10.
Unfortunately there is no Voltage (= 0V) at TP22, even the LED doesn't blink after I plugged the 9V in, so
I think it hast to be some bad welded contact. But I can't find any with my eyes. Where can I start to search?