To determine whether there is an internal circuit problem with an electric vehicle charger,observation and testing can be carried out from the following aspects:

　　Firstly,observe the appearance of the charger.If the charger casing has obvious damage,cracks,deformation,or heating deformation,it may indicate that the internal components are loose or the circuit is short circuited,resulting in abnormal voltage and excessive heat generation.This is one of the signs of internal circuit problems.At the same time,if there is any odor emitted,it should be immediately stopped and checked,as odors are usually related to internal component burnout or electrolyte overflow.

　　Secondly,conduct power cord and interface testing.Insert the charger into a functioning power outlet and observe if the power indicator light is on.If the power indicator light is not on,it may be a problem with the power cord or internal circuit of the charger.Next,connect the charger interface to the charging port of the electric vehicle and check if the charging indicator light is on.If the charging indicator light is not on or abnormal,it may indicate a fault in the charger interface or internal charging circuit.

　　Furthermore,use a multimeter for measurement.Adjust the multimeter to the appropriate voltage range and measure the voltage at the input and output terminals of the charger separately.Under normal circumstances,the input voltage should be AC 220V,while the output voltage varies depending on the charger model,but usually should be within a certain range(such as 36V to 48V).If the measured voltage value exceeds or falls below the normal range,it may indicate a fault in the internal circuit of the charger.

　　Pay attention to any abnormal behavior during the use of the charger.If the charger makes abnormal noises or vibrations during operation,it may be caused by damaged or loose internal components.In addition,if the charger charges for a long time but the battery level does not significantly increase,or the indicator light cannot turn green after charging is completed,it may also indicate that there is a problem with the internal circuit of the charger.

　　In summary,by observing the appearance of the charger,conducting power cord and interface tests,measuring with a multimeter,and paying attention to any abnormal performance during the use of the charger,it is possible to preliminarily determine whether there is an internal circuit problem with the electric vehicle charger.Once a fault is found with the charger,it is recommended to contact a professional repair service as soon as possible for inspection and repair.