Pressing the RESET button should have an effect on the LEDs, they should go off and back on again. That's concerning.
Yep that's not happening, led's still red, MACT & RESET buttons are working since they cut the voltage when press, so something could be holding the reset state.
If you put a DMM on the TX pin of J5, you should see the read-out changing for a while after you press the RESET button (or after a power cycle)
On J5-2 when RESET button is press, nothing happens, steady at -5.6v, but when power off, the voltage dips to -1.4xx, and to -5.6v when power on steady, it seems is stuck.
Did some more measurements with the unit power on:
Continuity test, J5-2 it's tied to C366, C364, C367, and to Maxim3232cwe pins 1,2,3,4,5,7,9,10,11,12,14,15,16
On C366 on one side I've 5.947v on the other side 0.0118v
On C367 on one side I've 5.605v on the other side 0.0001v
On C364 on one side I've 5.958v on the other side 3.279v
Seems that something is happening with Maxim
In attach there are the voltages of my Maxim3232cwe, I could try and plug pins 9 & 12 to a TTL --> RS-232 board with a Max3232, and see if there are some communication, what do you think?
If nothing of the above happens, most likely you have a faulty unit.
Let's see if I need to buy some new units.