hi thorsten,
sorry, i measured again more carefully this morning, and counted the pins more carefully.
so, with the USB plugged in i measure 5V on P2.1/RXD1 and 0V on P2.0/TXD1
(also i checked P0.1/RXD3 and P0.0/TXD3 and get also 5V and 0V respectively).
the voltage directly at the MIDI socket is 3.3 V at J12 and J20
(between middle/GND and square via / middle left pin of socket in rear view).
this confuses me a little since according to the schematic i would expect 3.3V on the right side (M+).
these voltages are the same with and without the ICs (IC1,IC2,IC4,IC5, LPC17) or jumpers (apart from J17) in their sockets.
to me the soldering looks clean, all blobs look concave, shiny and covering just the pad ...
and i also thoroughly cleaned the board with alcohol
(if it is possible to attach images here i could attach a picture of it?)
do you have further ideas of points where i could measure to find a short if there is one?
thanks,
Gerhard