Sorry to hear about the microUSB damage. It’s possible to develop a serial connection that bypasses the Unmatched microUSB port.
Please note that the UART signals on J8 are low voltage (1.8V). If you drive signals higher than 1.8V into the FU740 you can damage it. The receiver you connect to J8 may also need a level translator such that it can discern the 1.8V signaling from the FU740.
Using J8 UART with a host machine will typically involve two components:
- USB to RS-232 to TTL translator. Such as: https://www.mouser.com/ProductDetail/SparkFun/BOB-12731?qs=WyAARYrbSnbHMBc18Yr9rg%3D%3D
- Bidirectional level translator to convert 3.3V to 1.8V. Such as: https://www.mouser.com/ProductDetail/SparkFun/BOB-11771?qs=WyAARYrbSnbdm%2F0zn%2B5p2g%3D%3D
I haven’t tried these specific devices above, only describing the process. It also looks like the reference boards above may need soldering but there may be alternatives that don’t require soldering.
Note that permanent damage can occur if the UART signals are driven incorrectly - for example by higher voltage or with contention. They connect directly to the FU740-C000. There is also no specific ESD protection for signals on J8 so there’s a danger of damage by static electricity.