RDC6445GT5(EC) HMI-GT5 dead

Based on the described issue, it is normal for HMI 4-5 to be around 5V. Please provide the problematic symptoms of the HMI: Could you share photos or videos of the HMI when it's malfunctioning? If unavailable, you can also test the connectivity of the HMI's connection points (the interface between the mainboard and the HMI) using the continuity test function of a multimeter for 1-1, 2-2, 3-3, 4-4, and 5-5. If any of these connections fail to conduct, the HMI cable is likely damaged.

Based on your description, this does not sound like firmware corruption but rather a power or communication issue with the touchscreen. Your RDC6445GT5(EC) is clearly still running since the RUN LED is blinking and the machine works through RDWorks, which means the DSP core is fine. If firmware were corrupted, the whole board would typically fail to boot, not just lose the HMI.

The issue likely happened when you tied the limit input to ground, possibly causing a short, voltage spike, or ground reference shift that affected the HMI-GT5 power rail or serial communication lines. The fact that you measured over 10V between some pins is a major red flag, because the touchscreen is a 5V logic device. If 10–12V ever reached the 5V line, even briefly, the screen may have been damaged.

You should remeasure each pin relative to ground to confirm there is a stable 5V supply, and test the controller with the screen disconnected. If the 5V output is stable but the screen shows no backlight or activity, it is very likely hardware damage to the HMI rather than a firmware issue.