Electrical Gremlin in JD 757 Z-Trac

Discussion in 'Mechanic and Repair' started by Liberty Lawn Management, Jul 21, 2007.

  1. Liberty Lawn Management

    Liberty Lawn Management LawnSite Member
    Messages: 13

    I own a 2003 757. Just recently it's been blowing the main fuse after it gets up to operating temp, usually about 20-30 minutes. After that it blows it within a few minutes or seconds. I've gone throught the wiring harness as best I could and found no exposed wire.

    On a different note (This has been for about 1 year). The safety inter-connect has somehow gone haywire and will only allow movement of the machine with the PTO engaged.

    I appreciate any assistance with either of these!
  2. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    What's the engine?
  3. Liberty Lawn Management

    Liberty Lawn Management LawnSite Member
    Messages: 13

    Sorry, Kawasaki FH721D (25 H.P.)
  4. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Given the fact that you have a safety interlock problem, I would guess that if you solved this problem your fuse blowing problem could be solved also.

    First I would ohms test the PTO switch with a multimeter, Bad/burnt contacts inside could short out.

    Under your control panel you will see four relays, The second one from the front is for the PTO. The first one is for the starter. Swap the two then see if the unit starts ok, This will eliminate a bad/shorted PTO relay once warmed up.

    Some of these units have a optional interlock delay module, That could be heating up and shorting to ground also.

    Hopefully this little tid-bit of info. will help.....

    Good Luck
  5. Liberty Lawn Management

    Liberty Lawn Management LawnSite Member
    Messages: 13

    Restrorob I appreciate the info, and will test first thing tomorrow. I'm familiar with the relays. Any pointers on the interlock delay modules (Locations, What I'm looking for?)Thanks again!
  6. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    This is the only pic shown, If your unit does have this module it will be mounted in the control panel near the relays. I don't know if there is a test for this module, That's why I suggested checking the other things first.

  7. Liberty Lawn Management

    Liberty Lawn Management LawnSite Member
    Messages: 13

    Well it looks as though the PTO Switch is bad, I'll find one tomorrow. That should solve the interlock issue. Relays seem fine, I even interchanged with a known good I have. I checked the stator Coil Resistance. It was 0.3, Book says 0.01 - 0.1 is acceptable range. Would this possibly be causing the fuse problem? Lastly, there is a "Diode" (Thats what JD calls it) located on the wiring harness near the relays, it's a small red end cap, just wondering the purpose. Thanks!
  8. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Sorry I haven't gotten back, Had some computer problems.

    I really don't believe the 2 ohms difference would cause your fuse blowing problem. Did you check each stator lead to ground to see if it was shorted ?

    The diode only lets current flow in one direction, Example; Most charging systems have some type diode installed to prevent DC current from flowing back into a AC current output stator and burning it up.
  9. Liberty Lawn Management

    Liberty Lawn Management LawnSite Member
    Messages: 13

    Silly me, I did't zero the meter, stator is within spec's. Went through all connections on the mower (cleaned and checked). Ran fine today, so perhapse a week electrical connection was the cause for the fuse blowing. Tomorrow will be a better test though. Turns out the PTO wasn't the solution to the interlock problem. I'm still stumped. Thanks for the diode info, even the local shop wasn't sure what to make of it.
  10. fixer67

    fixer67 LawnSite Silver Member
    Messages: 2,098

    Diodes are also use to shunt back surges from things like relays and PTO clutches. If the machine has any fancy electrics diodes will be used on any device (relay, PTO clutch, and so forth) that could cause a back surge spike when switched off. When the electromagnetic coil is turned off and the field collapses high voltage spike can be produced. That is the basic way a ignition coil works.


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