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I have a SCAG STT52V-27CH, sn D7400052. Bought used last August, worked fine end of last year. Went to start this year, and fuse blows on yellow circuit when is turned on. Where should I start looking for problem. Thanks!

http://www.scag.com/OpManuals/STH/STHOPMANcomplete01043.pdf

Page 11 wiring diagram. Hands on, check all wiring for chafing, bad spots as in exposed wire where sheathing is missing, corrosion, loose connections and wire harness connections are on all the way at switches, relays, and ground connections are tight. You might have to purchase a multimeter tool, instructions included, and test circuits. This is an inexpensive tool that will serve you well, shop online for best price.

Hi wcwhite,
Attached is the wiring diagram for your machine. The yellow wire is the charging system positive. It is connected to the keyswitch and when the keyswitch is in the off position, the circuit between the red wires and the yellow wire is open. When the keyswiitch is in the on position, battery power is back fed thru the yellow wire, thru the fuse, down thru the harness to the engine connector. There the yellow wire, (may change color in the engine harness) connects to the output of the regulator/rectifier, which in turn is connected to the charging system stator located under the engine flywheel. I suspect that anywhere in this system there is a short circuit, and with a bunch of new 20 AMP fuses, you can disconnect the engine connector, then the regulator connector and then the stator connector to the regulator, one at a time and checking the fuse each time.
The reason the charging system is isolated when the keyswitch is in the off position is so battery power will not backfeed thru the charging system which will discharge the battery overnight. These charging systems are basic half wave systems and very different for the typical automobile alternator/charging system.
The attached wiring diagram does not show the Kohler engine harness, it connects to the connector labeled engine.
Let us know how things go for you troubleshooting this problem.
Mad Mackie in CT:laughing::biggrin::smile:

Mad Mackie:

Thanks for the starting point. I have a copy of the service manual for the Scag and the Kohler engine with the wiring diagrams, just wasn't sure where to start. I've got a vacation scheduled for a week or so and will be leaving this weekend. I will start on the troubleshooting when I return and will let you all what I find. Thanks again.

Okay, it was a bad regulator/rectifier. Engine running, not blowing fuses. Thanks for your help.

Hi wcwhite,
Glad we could help and thank you for telling us what resolved your problem.:thumbsup:
Mad Mackie in CT:laughing::biggrin::smile:

Okay, changed the rectifier/regulator and still blowing fuse. With the rectifier disconnected, the engine will start and run without blowing fuses. With engine running, I measured the DC voltage from the B+ lead from the stator to ground is 12.8; measured AC voltage across the stator leads is 19.9. With engine stopped, measured resistance across the stator leads is 0.1/0.2; measured resistance from each stator lead to ground is 1.4. According to Kohler CH740S Service Manual, stator leads are shorted to ground, so the stator is bad and needs to be replaced.

Does this make sense, as far as blowing the fuse, and the stator needs to be replaced? Thanks for a second opinion on this.

wcwhite said:

Okay, changed the rectifier/regulator and still blowing fuse. With the rectifier disconnected, the engine will start and run without blowing fuses. With engine running, I measured the DC voltage from the B+ lead from the stator to ground is 12.8; measured AC voltage across the stator leads is 19.9. With engine stopped, measured resistance across the stator leads is 0.1/0.2; measured resistance from each stator lead to ground is 1.4. According to Kohler CH740S Service Manual, stator leads are shorted to ground, so the stator is bad and needs to be replaced.

Does this make sense, as far as blowing the fuse, and the stator needs to be replaced? Thanks for a second opinion on this.

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The AC volts are low should they be up around 28 volts. resistance across the stator also seem low, I would also say go for a replacement of the stator, but the odd thing is you say in post 5 "it was a bad regulator/rectifier. Engine running, not blowing fuses." which makes you think is it a bad wire coming from the stator, you do not say how long it run for before it was blowing the fuse again.

I assumed it was a bad regulator/rectifier when I disconnected the stator leads and turning the key on didn't blow the fuse. Then the engine would start and run. So I changed the regulator/rectifier and still had the problem. Went to the Service Manual and ran the tests on the charging system. With the results shown above, now thinking it is the stator. Looking for second opinion to confirm changing out the stator too. Thanks.

The stator should have no reading to ground and read infinity or open circuit on a ohmmeter. But check the stator wires from the regulator connector to the stator itself.

Okay, I got the flywheel off. The magnets around the the stator were broken and loose. Is there a part number for the magnets or are they a part of the flywheel? I don't see them in the parts list. Thanks!

Mad Mackie said:

The stator should have no reading to ground and read infinity or open circuit on a ohmmeter. But check the stator wires from the regulator connector to the stator itself.

Click to expand...

Time for a new flywheel and stator!!!

Woohoo! Installed new stator and flywheel, and all is right now. Cut grass today, no problems at all. Thanks for the help.

Thanks for the update:thumbsup: