If the charger is completely "dead" with no lights, the main power transistor often needs replacement.
A standard diagram for this board reveals several critical sections:
Because these chargers are used on job sites, dust and moisture can lead to poor contact at the B+ and B- pins, triggering "Charge Suspended" errors. Safety Warning
This section provides the DC voltage used to charge the battery cells. It includes diodes for rectification and capacitors for filtering the output.