By hvhipot 
If the loop resistance tester has the following failure phenomena, the troubleshooting methods are as follows:
Trouble phenomenon:
1. There is no response after booting, and the LCD screen has no display
Troubleshooting: 1) Check whether there is AC power supply;
2) Check the power cable;
3) Check whether the fuse in the fuse base is blown.
2. During the test, the resistance value is obviously too large or displayed as over-range
Troubleshooting: 1) Check whether the measured resistance value is too large;
2) Check whether the voltage input line is connected to the inner side of the current output line;
3) Check whether the polarity of the test line is reversed;
4) Check whether the voltage output line is connected well, and whether the joint of the test piece is oxidized.
3. No response when rotating the mouse
Troubleshooting:
1) Turn off the power and restart;
2) Press the reset button to reset the instrument.
4. Communication is unsuccessful
Troubleshooting:
1) Check whether the data cable is connected properly;
2) Check whether the instrument is online;
3) Reinstall after uninstalling the driver;
4) Press the reset button to reset the instrument.