Sometimes this can be misdiagnosed as a bad charger or a bad charger control board. It appears you have a charger problem when in fact you may have a battery problem.
In the majority of cases the golf cart has sit for weeks or months and the battery charge has drained down below the acceptable level of 28 volts for the charger to turn on. If this this the case all you need to do is check the voltage coming out of your entire battery pack to figure out how much voltage you really have. You can also attempt to charge each battery with a standard battery charger for 2-3 hours per battery to help get the total battery pack voltage above 28 volts.
Golf cart chargers must sense 28 volts coming from the batteries in order to even turn on. Any voltage from the batteries less than 28 volts would not allow the charger to turn on.
To check and verify this information please see the attached pictures.