Motor tripping fuse when switched on

The most obvious reason for the db board trip to trip is current overload. Current overload in a case like this is normally due to a short. The first thing thus is to test for this while the machine is static (ie disconnected from the supply):

Connect your ohm meter (lowest setting) to both the machine's supply terminals. A zero reading will indicate a 'dead' short somewhere along the cable or in the machine itself.

To eliminate the cable, open the machine and locate where the supply wires go. Disconnect them. Measure the disconnected ends - they should read infinity (ie open cct). If a zero reading is obtained, replace the cable. If the supply cable is not shorted, read the input terminals in the machine while you close it's start switch. If OK they should not read zero which will indicate a shorted field or armature wire. A reading of a few ohms, say around 20- 50 ohms will indicate you are measuring the field wiring. Now spin the machine by hand (try to locate where the motor shaft connects with the resiprocating base plate). Loosen it if necessary to be able to turn the motor by hand. With the ohn meter leads still connected, turning the motor either way will cause the meter needle (an analogue multimeter is best for this purpose) to move either way in concert with your turning the motor. A digital meter will alternately show a positive then a negative reading. This will indicate the motor is probably OK.

Failing to detect your short this way leaves a dynamic short: could be worn brushes, a starting/running capacitor or control cct problem.

An eye inspection will often reveal burnt field or armature winding wiring.