I have a custom designed board that basically functions as an ethernet switch. On it I have 4 ports 3 with magnetics and 1 without magnetics. I could not use integrated magnetics on all of them because the last port is heavy duty and didn't come with that options.
The behavior I am seeing is that if I use any combination of the 3 with magnetics then I can connect to the internet just fine. All of them recognize in seconds. When I use the port with discrete magnetics the internet only works sometimes and without any real pattern as to when it will or will not work. Sometimes I can get connection by unplugging and replugging but there is no consistency.
Things I have tried/check:
- Differential pair impedance 0.25mm with 0.2mm between - same as all the other ports
- Tx/RX length matching - both pairs are within 5mm of each other.
- Changed out ports on board
- Tried different cables
- Unplugged and replugged on both laptop and board side. Will sometimes fix the problem but not reliably.
- Tried another board of the same design without any change.
- Inspected board for any assembly defect.
I really have no idea what could be the problem it seems to be a problem with my board but there is nothing I can think of.
EDIT: More specific details of what circuit entails.
- Switch IC KSZ8895MQXCA
- Mag Jacks: JDL-0011NL
- Magnetics: TG110
- Non-mag jack: MRJR-5381