Yaesu FT-901DM Maintenance Service Manual page 76

KEYER UNIT MODIFICATIONS
Several minor changes were made during the
production of FT-901DM units using the Curtis
8043 IC. The diagram below represents the final
version of the KEYER UNIT, and if you should
have to perform service on this board, we
recommend that the circuit be modified as shown
here.
CURTIS 8044 IC CIRCUIT MODIFICATION
Beginning with the No. 8 production lot, the Curtis
8044 IC was used in the KEYER UNIT. The 8044
includes both dot and dash memories, and several
changes were made in the circuit board to reflect
the use of the new IC. Notable among these was
the removal of the symmetry control.
The corrected schematic for the 8044 IC KEYER
UNIT is shown below.
3-21
SERVICING