The UP9600 hack does not work on the C128 computers. By default, the WiModem is shipped with this hack is enabled. To disable it, you need to cut one jumper. There are actually 3 jumpers that control the UP9600 hack, but only one interferes with the C128's SRQ line used for burst mode, which will prevent the IEC bus from working while in C128 mode with 1571 & 1581 drives (including the C128DCR). C64 mode works fine. Only the C64 can take advantage of the UP9600 hack, which gives you the ability to run the C64 at 9600 baud.
Cut the trace that is between the two jumper pads shown below. To restore the hack, solder between the two pads. You can reach these pads even with the OLED screen. If you feel that this is too difficult for you to do, then return the board to me and I will ship you a version with all of the pads cut to disable the UP9600 hack completely.
Cut the trace that is between the two jumper pads shown below. To restore the hack, solder between the two pads. You can reach these pads even with the OLED screen. If you feel that this is too difficult for you to do, then return the board to me and I will ship you a version with all of the pads cut to disable the UP9600 hack completely.