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Then again the SCR board I repaired on the 1974 model blew the SCR's to pieces which makes me think there could be some pretty high back EMF generated when power is turned up. The 2 wires that go to the reactor core are pretty light gauge.
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If it will work with just a 0-30 volt DC driver circuit I would be game ( but have some serious doubts).
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How to build a simpler drive circuit than what Lincoln eventually ended up with, before they changed the reactor core part number, it used a single driver card that incorporates the diode board and SCRs. It is too bad that it doesn't include a higher quality schematic diagram.Yeah that's where I get hung up. I'm not sure exactly how the magnetic amplifier works, but it is pretty simple as long as any critical parts aren't burned up. The fine current control is accomplished by the "magnetic amplifier" that sends a DC voltage to magnetize the "reactor" core that the coarse current switch selects the number of windings on the reactor. It has a very useful trouble shooting guide for the problem here.
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That is a very nice user manual that was written at a time when machines were intended to be repaired. If not shorted or completely open then an Inductance test of those windings. Then a resistance test of the MAG amp windings is where I would go next.
All of the diodes in this old of a welder are Selenium and definitely could be suspect. Next a break over test of all the diodes- near the MAG amp. If so the main transformer windings are probably OK. But I am switching over to my BILs TIG 300 300 and putting mine away since he has never come to get it or until he does.ġst test is to verify just over 70 volts at the output studs. Lincoln may be able to supply the wiring diagram if you request an email of the schematic.Įven with the half baked repair on my TIG 300 it will still TIG /stick weld to over 370 amps if needed. The OP may be lucky and just have a bad wire or bad rheostat or other problem.
changing the main current control (1000 ohm) to a 10k ohm unit as well, the foot pedal would also need a 10K wire wound pot Would also need the SCR / diode board and Caps. If there were some boards still around from the 1970's models (and I had more free time to play with the wiring on mine) (right now i just don't) I would try and copy the newer models wiring since I believe the main reactor core and output windings have the same number. On an Oscilloscope the output current is not the same on the + and - wave and does not match the newer SCR drive TIG 300 300 in my Sig which works correctly. It "works" but is not "right" I can't lower the amps down below about 15 amps on the lowest setting. the previous owner (a college) removed a single diode (out of a bridge rectifier) on the reactor drive and then wired the buck winding as the driver. Lincoln used a Boost Buck double winding in the center of the Mag amp assembly. I agree scrap it if you cant get the amps to vary.If it leads to your hair falling out or pulling it out.īecause that is an early TIG 300 300 and from my experience with my 1962 model, a possible and maybe even likely cause of not being able to control current output is because the Magnetic amplifier windings are burned up/broken and there are no replacement MAG amps from Lincoln. You can buy a much better, and much smaller, welder for under a grand.Īgree and disagree with Louie on this one. But honestly unless you have a crap ton of room in your garage or shop, I say scrap it. In the past I would have been in the fix it camp.