Lincoln SP 175 MIG welder

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I have a Lincoln SP 175 MIG welder which has developed a problem. When welding, the circuit board will occasionally turn off the wire feed motor, arc and gas but not the cooling fan. Releasing the trigger and immediately reengaging it will return welding function. I believe the two over current sensors are not at fault because I assume they are bi-metal switches which would take a while to cool and reset. The friendly Lincoln repair facility wants to replace the entire circuit board! So much for "techs."The manual does not include a schematic of the control board but it appears a relay control is sensing a over current fault. Perhaps an over temp or excessive wire feed motor current.I have been into circuit boards before but I need a schematic. Any ideas???
Reply:http://www.lincolnelectric.com/asset...OLN3/IM790.pdfThermal switch, wire feed brake to tight overloading wirefeed motor, or fuse.  Try loosening the wing nut in the middle of the spool to allow the spool to spin easier.  This will put less strain on the wirefeed motor.  I sent my 175 HD into thermal shutdown once and it took a few minutes to work again.  The brake should be tight enough so that when the wirefeed motor stops pulling the spool doesn't keep spinning.  Parts manual for SP 175.http://www.lincolnelectric.com/asset...coln1/p460.pdfLast edited by 85cj7boy; 09-27-2011 at 10:12 AM.
Reply:Thanks for the reply. I have adjusted the tension on the wire feed motor to no avail. My next shot will be to measure the current draw on the wire feed motor. Then, contact Lincoln and see if they can give me a "normal" current draw on the motor. If the current draw is within specs, at least that part will be eliminated.
Reply:When you say tension on the wirefeed motor are you talking about the drive roll tension or the spool tension.  Drive roll tension should be adjusted to the point that you cant keep the wire from coming out of the tip but no tighter.  Start with it loose and grab the wire with some pliers while you squeeze the trigger.  You should be able to hold the wire and the drive rolls will spin on the wire.  Tighten that wing nut a little bit until you can no longer hold the wire back at the contact tip.  The spool tension might actually be a nut inside the center of the spool instead of a wingnut like i mentioned earlier.