Replace DG board first, fault constant, measuring between groups stabilized output voltage is normal, heat circuit board parts failure remains. Doubt U plate has a problem, but without a replacement at hand. Oscilloscope measurement A4 each foot level, found that eight feet SCL2 only 3.3 V, A1101 28 feet only 3 V (5 V) for normal, take U plate over the ground resistance measurement, 27 feet for 8 K, 28 feet only 2.2 K, and use soldering iron to heat LC1101 ground resistance after back up to 8 K, commissioning failure again, 2 hours after replacing LC1101 normal commissioning for a few days, troubleshooting.Wk3service manual download site