You need to test the field coils to make sure its not them, if it is you will waste cash rewinding the armatureIf the welder does not supply voltage anymore, please do the following checks:
b. The machine doesn't supply voltage. Disconnect the capacitors and, with an analogical (select the reading scale in Ohm X100) verify if there is a short circuit on one or more capacitors. If there is no short circuit, reconnect the capacitors to the stator, start the machine, put it at maximum Rpm and with 2 cables connected to a starting battery (12V cc), feed for an instant 2 poles of one of the capacitors in order to have an external excitation (please pay attention in doing this operation as, if the machine starts to supply voltage, on the capacitors you have a linkage voltage of about 400V). If after this operation the machine does not supply voltage, the fault is surely in the alternator.
- disconnect the cables coming out from the alternator which feed the diode bridge (no. 11) and disconnect the cables which feed the distribution panel (this is to avoid a possible short circuit which could de-energize the machine). Please note that all the disconnected cables have to be insulated and numbered in order to reconnect them in the right position
after this test.
- Start the machine and put the machine at maximum Rpm, at this point there are 2
possibilities:
a. The machine starts to supply voltage. In this case there is a short circuit either on
the diode bridge or on the front panel.
In order to find out where you have the short circuit, do the following test: stop the machine and reconnect to the diode bridge one of the cables previously disconnected and verify, starting the machine, if it supply voltage. If you have voltage, reconnect to the diode bridge the second cable 11 and start the machine once more in order to find out if it supplies voltage. Do the same test with the 3rd cable 11. In case after having connected one of these cables the machine does not supply voltage, check the diode and the SCR connected to the phase that has de-energized the machine.
In case after having reconnected all the 3 cables to the diode bridge the machine continues to supply voltage, then check the front panel.