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Another busted Trailblazer 251 with only 290 hours! Anybody have bad PC2 boards?

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  • denwhit
    replied
    Fixed it!

    After getting good ohm readings across the diodes in the bridge rectifiers, yet getting screwy voltage readings, I just decided to replace them both. That worked! She's back to performing like a new one. I guess the lesson is that when the actual current hits those rectifiers, the real test begins. Anyway, my thanks to everyone who participated with help and advice.

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  • denwhit
    replied
    Originally posted by walker View Post



    While while testing, I bumped a wire and it sparked. Just pull apart your molex connectors to check for corrosion, and loose ones will make themselves apparent.
    thanks for that

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  • walker
    replied

    Originally posted by denwhit View Post
    I hope mine turns out to be that easy (cheap fix). What reading, voltage or resistance, showed the problem?
    While while testing, I bumped a wire and it sparked. Just pull apart your molex connectors to check for corrosion, and loose ones will make themselves apparent.

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  • denwhit
    replied
    Originally posted by Can You Weld This For Me? View Post
    Just want to triple confirm, you do have the output contractor switch "ON" correct?
    Both switches are in the up position.

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  • Can You Weld This For Me?
    replied
    Originally posted by denwhit View Post
    Have power at the convenience plugs but no weld power.
    Just want to triple confirm, you do have the output contractor switch "ON" correct?

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  • denwhit
    replied
    Originally posted by walker View Post
    FWIW, mine turned out to have a broken wire in one of the wires going down to the slip rings. The terminal in one of the molex connector cracked. Since the other wires were fine, that one stayed in there, but didnt excite the generator.
    I hope mine turns out to be that easy (cheap fix). What reading, voltage or resistance, showed the problem?

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  • denwhit
    replied
    Originally posted by duaneb55 View Post
    And your resistance reading between the center and front rings is a little low and should be 31ohms but the exciter rotor would be good at 12-12.5ohms.
    Had a minute this morning to check those out and I get 30.8 and 12.1 ohms.

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  • walker
    replied
    FWIW, mine turned out to have a broken wire in one of the wires going down to the slip rings. The terminal in one of the molex connector cracked. Since the other wires were fine, that one stayed in there, but didnt excite the generator.

    Leave a comment:


  • duaneb55
    replied
    I wouldn't throw in the towel just yet.

    Enjoy the vacation!

    BTW, if you can't find me here on the Miller sight, I spend most of my time over on WeldingWeb http://weldingweb.com/forumdisplay.p...&s=&daysprune=

    Leave a comment:


  • denwhit
    replied
    Originally posted by duaneb55 View Post
    And your resistance reading between the center and front rings is a little low and should be 31ohms but the exciter rotor would be good at 12-12.5ohms.
    I'll check those when I get back from a four day short vacation. When I get back, I'll take all of those resistance readings. Is anyone looking for a low hours 20 hp Onan motor? I'm about to give up. If it's PC2 or the windings, I think it's totaled and will part out. Thanks for your help, I really appreciate it.

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  • duaneb55
    replied
    And your resistance reading between the center and front rings is a little low and should be 31ohms but the exciter rotor would be good at 12-12.5ohms.

    Leave a comment:


  • duaneb55
    replied
    Yes, LED #2 and #3 should be lit when the board is energized.

    Did you check DC voltage between the center and rear slip rings?

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  • denwhit
    replied
    LEDs on PC2 are not lit

    Should two of these be lit?

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  • denwhit
    replied
    Originally posted by duaneb55 View Post
    I appreciate the compliment but I'm no expert by any stretch of the imagination. I'm more the blind squirrel that finds a nut once in awhile. If you're now only getting 24VAC at the auxiliary outlets my guess is you're only getting 12VDC flashing voltage (battery +) across the brushes. If that's the case, I would check for a blown exciter output fuse F1 and/or failed exciter bridge rectifier SR3 for starters.
    SR2 and 3 are good, fuse F1 is good, I cleaned the rings and the brushes are making good contact. Had about 24 ohms between front ring (from control panel) to middle ring and about half that from middle to back ring.

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  • duaneb55
    replied
    I appreciate the compliment but I'm no expert by any stretch of the imagination. I'm more the blind squirrel that finds a nut once in awhile.


    If you're now only getting 24VAC at the auxiliary outlets my guess is you're only getting 12VDC flashing voltage (battery +) across the brushes.

    If that's the case, I would check for a blown exciter output fuse F1 and/or failed exciter bridge rectifier SR3 for starters.

    Leave a comment:

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