Sears PTO clutch problem

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  #1  
Old 06-07-08, 06:56 PM
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Sears PTO clutch problem

Craftsman lawn tractor. Model # 917-273632,18.5 HP-42 inch mower deck. When engaging PTO, amp meter indicates full short to ground. I believe I have isolated problem to electric clutch. Wiring diagram shows a diode in parallel with the clutch coil. I believe diode may be shorted. Is the diode internally mounted in the PTO clutch? Can not otherwise locate diode. Thanks for any information available on my problem
 
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Old 06-08-08, 08:46 PM
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I'm not looking at a diagram for that, but I know of no diode on those mowers other than the one on the charging stator.

If your mower is not charging (have you tested it?), then this diode could be bad, and is found on the red wire coming out of the charging stator under the engine flywheel.
 
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Old 06-09-08, 11:02 AM
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I have the Sears wiring diagram. There is a diode across the clutch coil. When applying 12VDC to the clutch coil wire the amp meter indicates a maximum discharge. The battery is charged. The alternator produces the nominal voltage of 12.9VDC...With the engine running and applying voltage to the clutch coil the PTO engages, but the amp meter shows a max discharge and if the voltage remains applied to the coil the system fuse will blow in about 15-20 seconds.
 
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Old 06-09-08, 09:32 PM
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Sounds to me like the clutch coil is shorted. To which wires is the diode connected, and which way is the polarity oriented?
 
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Old 06-15-08, 08:59 PM
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Diode Location

In dealing with a non-functioning electric clutch I found what appears to be a burned diode. It was located on the harness side of the electrical connection with the clutch.

It is right next to the connection and covered by heat shrink tubing. It runs between the positive and negative wires (red and black)

slice the shrink tubing lengthwise to expose it.
 
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Old 06-16-08, 11:58 AM
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Thanks for the information. If it ever stops raining here in Tulsa, OK, and the ground dries up, I will attempt to locate the diode.


Originally Posted by dlkassel View Post
In dealing with a non-functioning electric clutch I found what appears to be a burned diode. It was located on the harness side of the electrical connection with the clutch.

It is right next to the connection and covered by heat shrink tubing. It runs between the positive and negative wires (red and black)

slice the shrink tubing lengthwise to expose it.
 
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Old 06-25-08, 07:29 PM
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Problem solved!!

I found the diode, its located at the first disconnect from the clutch housing. It checked OK. I removed the clutch, ohm metered it and it indicated it WAS SHORTED. Found a repalcement on the 'net and at a price less then half of Sears cost. Recieved it today, installed it and mowed that once tall grass. Thanks to all that replied, it was much appreciated.
 
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Old 06-27-08, 12:52 AM
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Glad you got it fixed, and thanks for the update. I haven't seen or at least haven't paid attention to a diode on that circuit before, so now I know. I suspect it is probably there to discharge the voltage spike from the collapsing magnetic field in the coil to ground instead of letting it backfeed the positive side of the system with a spike that could harm more sensitive components.
 
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Old 06-27-08, 08:53 AM
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there to discharge the voltage spike from the collapsing magneti

Sometimes they just use a resistor for this. They're probably more reliable.
In this case if the normal current draw is I, the highest voltage spike you get is I x R.
 
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Old 06-27-08, 10:32 PM
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ok,

I don't think a resistor is used for this application...as the diagram specifies a diode and a resistor would not work in this application. Reliability isn't an issue, as diodes don't generally give trouble in the first place. The equation doesn't make sense mathmatically or electrically.

I'm not trying to be mean, but I can see your post confusing a lot of folks who are trying to figure out this problem with their mower for themselves. Thanks anyway for trying to help, but I wanted to clear this up for those who will read it in the future.
 
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