Encounter this type of problem, at first you need consult the customer if he hears the sound of the cash drawer.
1) If there is a sound:
First confirm whether the bottom lever of the cash drawer can be used to open or use the key to open (the three gear lock cash drawer has one gear which can be opened directly using a key). If it cannot be opened, it may be the cash drawer at the locked state.
Second If there is no problem with the above, then we need to check the voltage of the printer and cash drawer and the supply voltage of the cash drawer needed.
Final Check again whether the paper jam causes the cash drawer can not be opened. If there are no problems, it may be caused by insufficient elasticity of the cash drawer spring or an electromagnet problem.
2) If there is no sound:
it may be caused by the problem of the cash drawer interface. This kind of situation needs to take the replacement test (the printer also needs to confirm whether there is an option to open the cash box in the drive item).