50Ω Ohms is somewhat low and without the Terminator RJ45 in J8 you should measure ~120Ω —- There should be a jumper across JP3 on the M1 main board. Make sure JP3 on the M1 is in place — power down the M1 System and:
- Unplug each Bus Devices from the M1DBH
- Connect the RF45 with built in resistor into J1 on the M1DBH
- Measure the resistance which should be ~60 – 70Ω
- If so then move the RJ45 to J2 and connect a device to J1 and measure again
- Keep repeating this adding another device to the M1DBH and moving the RF45 with Resistor to the next port and measuring the resistance
- Each time you should measure between 60 – 70Ω