While testing the conditional branch, I saw that the value of the instruction register was not correct...relay for bit[4] of the instruction register was not able to store the information. The result of this problem was that the BZ (branch if the value stored in the accu is zero) was not working.

But i have 3 spare relais in the instruction register....bit[0..2] are not used at the moment. So i changed the wiring to use relay[2] instead of relay[4]...and the BZ command worked fine.