I am still at calibration stage and need some info from the PCB. I connected the USB and ran Repetier. The PCB wants to talk at a higher baud rate than my serial port says it can do. I tried setting the serial port to its highest setting 125k and reduced the PCB baud in Repetier setting to 125k. No joy. PC port reverts to 9600 every time I check it. Thoughts?
PC running Windows 7 Home Premium 32bit.
Are you sure that the A8 connects to a PC using a serial port? I don't know of any 3D printers that do that. Typically, 3D printers connect to PCs using a USB connection, and there will be a type-B USB socket on the printer.
However, there will be a USB bridge chip on the printer's controller board that connects the microcontroller to the USB socket. This bridge chip does have a serial port that is used to communicate with the microcontroller. Typically, these serial ports operate at 115,200 bits per second (115.2 kbps), although this may vary. Some USB bridge chips are capable of operating at 250kbps.
Often, the software running on the PC needs to know what speed the serial port on the bridge chip runs at, in order to send data at a suitable rate. Of course, the USB connection is capable of handling data at a much higher rate, but the microcontrollers used in many 3D printers are not capable of handling such speeds.
Note that the USB bridge chip on the printer may appear as a virtual COM port on a PC.