First check the power supply circuit, power circuit have been found to work properly. Check TB1237AN voltage 3 feet, also is normal, check voltage, 8 feet also normal. Use oscilloscope to detect 4 feet, no conduct pulse output, 4 feet of dc voltage is not normal (only about 0.5 V). Waveform measured again 1 foot, also do not have sandcastles pulse, doubt TBl237AN damage, after replacement, troubleshooting. Note that TB1237AN integrate block TB1238AN is not same, their structure is totally different, cannot be used to replace TB1237AN TB1238AN.BXxservice manual download site