SA 250 no arc

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Recently picked up a SA 250 (code 8917)  that starts, runs, and produces power at the auxillery outlets.   It won't strike an arc,  only shows 7 volts between the studs for the leads.   Need advice on where to start checking.   Thanks
Reply:Check the weld brushes. Open the doors and there should be a cover going  around the generator. Check to make sure the brushes are free and not stuck.
Reply:Also could be your rheostat. Had a buddy with same problem a week ago and it was his rheostat
Reply:Have been studying the wiring and parts diagrams and not many external parts to check.   The brushes were the first to be checked and seem to be making good contact.  What would I be looking for in checking the rheostat, full wave bridge, reed relay, and the pc idle board?  Thanks for the suggestions.  Keep them coming.
Reply:follow your excitation circuit. from the source through the controls to the generator coils.look for bad connections and broken wires.
Reply:Rich68,This sounds like it's headed for shunt coil problems.May as well concentrate your troubleshooting there.Good Luck
Reply:Checked all the external wires, rheostat checked at 64 ohms.  Is there a way to check the idle board  and reed relay to be sure they are good.   Looks like Denrep's suggestion of shunt coils is where we are headed.   Thanks
Reply:Decided the shunt coils are the problem .    Is there a trick to getting the exciter armature off or is this one just really stuck?
Reply:bend back the locking washer and use a large six point socket. breaker bar or impact wrench. when you put it back together use a dial gauge to get it centered. Try not to bend shaft.