hi, remove u412 and connect ttl adapter and test. maybe u412 connects to some mcu and your comm is affected.
converting from ttl to rs232, why?
Hmm,
I did test the pins out on u412. Pins 2 and 3 are connecting to the db9 serial connector on wires gray and white. Pins 1, 4, and 7 connected to ground.
Pins 5 and 6 to the DS80C323 and I just realized I didn't trace pin 8. And, the path between pins 2 and 3 may be intercepted as didn't review the path end to end.
As to why covert to RS232, I don't have a good reason other than what is there isn't working, the pad is available and other units such as this with different options have the MAX232 chip installed. Yeah, not good reasons.
You gave me a couple of ideas and I'll try that. I don't recall probing the traces between the small chip and the DS80C323 microcontroller.
And removing this small chip isn't a bit deal and I can tap right onto the pads for TTL.