Checking for parasitic drain on riding mower

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  #1  
Old 08-02-15, 04:55 PM
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Checking for parasitic drain on riding mower

Hi everyone,
So I am chasing a parasitic drain on a neighbor's John Deere stx38 black deck mower.
family skh398u122rb
model cv139 spec 21509
serial 2704801142
id moostxj299848
(this taken from his notes)
Long story short he can hook a test light in series with the negative terminal and it will light. Hook an amp meter and if memory serves he is getting around .4 amp draw.
The only way we have found to stop the draw was to unplug the regulator. Key off engine off the middle terminal is getting battery voltage. For other reasons his key switch has been replaced as well as the stator and regulator. His old switch was .....gunky....inside and I figured he has some bleed over but new switch and he still has the same problems. I could keep writing but will shut up and see where this much info takes me....
long question short - key off there should be no draw on this system right?
thanks folks!
 
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Old 08-02-15, 05:06 PM
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Usually when the key is off there should be no drain.
Do you have a wiring diagram for the tractor or are you just guessing around ?

Found a good service manual for you with diagrams. Section 4 has the wiring diagrams in it and are based on the mowers serial number.
drive.google/file/d/0B_XZLMkMeCkdeHhPWE9Gd0pYdVk/edit?pli=1
 

Last edited by PJmax; 08-02-15 at 05:25 PM.
  #3  
Old 08-02-15, 05:33 PM
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he gave me his service manual to look over and if I read it right it covers sn 210001- so I have a schematic. I'm not following the layout just yet, but it looks like there is a red from battery + that joins a red to the middle wire of the regulator as well as an orange wire to the key switch.
I'll have to verify that orange wire but everything looks like the way it is wired up now. It starts and runs fine, just that little draw.
 
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Old 08-02-15, 06:16 PM
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I posted before I saw the edit - that is the same service manual he has (big thanks for the link though). Would have been nice to include a section for key off engine off test points :-) . I'm overlooking something.
 
  #5  
Old 08-02-15, 07:03 PM
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Check to see if the stator is messed up from loose magnets under the flywheel... been seeing a lot of that lately. If so, replace. If not, try another regulator.
 
  #6  
Old 08-03-15, 12:45 PM
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Why am I thinking there is a relay that disconnects the regulator from the battery on these?? See if it has one. Maybe the contacts are stuck closed in it.. Roger
 
  #7  
Old 08-03-15, 09:42 PM
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There is no relay disconnecting the regulator shown in the schematics.
 
  #8  
Old 08-04-15, 08:41 AM
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no, no relay on this one but I have seen people add them and there are in some of the other series. I just ran over there and this is what I found so far. I can make the drain go away by unplugging the connection to the regulator/rectifier. I can also make the drain go away with the regulator plugged in by disconnecting the short black wire that goes to ground from the regulator. It looks like the center wire on the regulator connection is 'hot' all the time by design but the regulator is seeing a ground when it should not be. Does that make sense? The stator is showing no continuity to ground so is the regulator grounding when it should not be? That is all I can come up with.
 
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Old 08-04-15, 10:13 AM
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Yeah, it sounds like you narrowed it down to the regulator.
 
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Old 08-04-15, 10:47 AM
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he isn't going to want to hear that.......brand new one but that is the only thing that makes sense. I will dig his old one out and see if it does any different.
thanks folks as usual and I will update with a final solution
 
  #11  
Old 08-06-15, 05:24 PM
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Well, the old regulator acts the same as the new one. That's not to say they both aren't bad but I doubt he wants to get another one just yet........final outcome delayed.
He said he replaced the regulator/rectifier and stator because the running tests showed no charging. The new set (and possibly the old set) show good charge now but of course the draw. He said when he took off the flywheel there was a ton of dirt and crud under there. Doesn't change the outcome much, just providing more info for future reference.
 
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