chstewart
So I was hit by the storm on Saturday lost power and have yet to get it back. :( So I decided to start my generator before I lost power to be ready, it started ran for a bit then smoke came out of the control box
It is generac primepact 70G model 5951
The charging rectifier is Burt to crisp. It runs fine but only getting 3 volts out of the generator. Checked DC voltage at brushes and only seeing just over 1 volt DC. Brushes look fine but one is shorter then the other (is this normal?). I assume next step is to check ohms reading across the rotor but don’t know which two leads and what should the reading be? I was hopping it was just the voltage regulator board went bad but thinking it’s a lot more.
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chstewart
Hope to get some help. So i took wire 4 off VR and flashed the field voltadge came up to 90vac and the red led on the VR light up and droped as soon as i pulled the 12 volts.
16 Ohms between 4 & 2

what is my next step in finding the issue?
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MikeyfromNC
according to the schematic I found online, wire 4 goes from the voltage regulator to a PCB. Without knowing more about the PCB, it would seem to be a crap shoot....i would focus on the magic smoke. The rectifier burnt, so the question is why. Over voltage or a hard ground possibly?
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MikeyfromNC
PCB board--wire 4 from the VR goes to j1-9 on the PCB....J1-10 on the PCB is from the battery charging rectifier...are those two terminals on the PCB connected on the back of the board?
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chstewart
Wire 4 goes from J1-9 on the control board to VR to brushes
J1-10 is wire 66 that leads into the harness that goes to the rotor. When I got this unit it did not even have the charging rectifier in it, and was running fine I put a new one in works fine got me throe Irene and a few other short outages.
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chstewart
Yes J1-10 goes to the charging winding
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chstewart
corect me if I am wrong the PCB flashed the brushes but the VR board then provides the voltadge to the brushes. so if the VR is not putting out volatadge to the brushes it apears to be a bad VR?
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MikeyfromNC
quite honeslty I'm not sure. I would need to get my hands on it along with the prints. This is not something I am comfortable working on. Is the warranty up?
I am still thinking about why the rectifier get fried. If the VR was bad why would it smoke the rectifier? It doesn't look like they are directly connected, other than through the PCB somehow. Just thinking out loud.
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douglas123
Give me a little bit. Had to work 1/2 a day today and need to run to the store for a bit. When I get back I will pull up the schematics for your unit. Could you post the serial number of your unit so I pull up the correct schematics. Back in a couple of hours. PM me your E-mail address and I will get them to you asap.
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douglas123
Ready to help. Need serial number before I can pull up schematic.
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chstewart
Model 0005951
SN 3559529
I was able to get a spare VR to test with same results 7 volts ac. no voltadge at the brushes. If I supply volatadge to the brushes the generator puts out power. I suspect the charging winding provides power to run the VR board which power the brushes and I am betting those windings are tost. If you have the drawings can you confirm this and give me which wires I should check across to confirm the winding is shot.
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douglas123
Send me your Address via PM and the schematics will be there shortly.

Douglas123
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