Hi, I have the Meldas M500 control which should be very much the same.
If all comms are set up correctly, this is the procedure I use for DNC:
1) Get DNC program ready for DNC dripfeed
2) Set machine to "Tape"
3) Push "Monitor", then "Search"
4) Type the program number in the O( ) field
5) Change the DEV(0) field to DEV(1)
6) Tell my DNC program to begin dripfeed
7) Press "Input"
8) Cycle start
Can answer any other questions if this doesn't help.
I googled the M50 control and I think it is similar.