This entry is just a memomrandum.

Last week I made a sum-amp circuit to add the offset to PDH feedback signal.
But the output from the circuit did not contain the input signal, i.e. insensitive to the input signal and could not use though I confirmed all the conduction was fine.

Actually, there was a problem at one op-amp port labeled 5 on the board.
By changing the port, this problem was solved, but what caused this was uncertain...

One possible reason is due to the poor soldering around the op-amp but not sure.