I have a John Deere F510 riding mower that keeps blowing the PTO fuse.
The strange thing is that it does not blow it right away, and it
doesn't always blow it. Here are the sysmptoms:

1. I put a fresh 15 amp fuse in the PTO.
2. Start up the mower, it runs fine.
3. Engage PTO, it works fine.
4. Mow the yard for at least 10 minutes, it works fine until the first
time I disengage the PTO.
5. Once Disengaged, the PTO will not work again.
6. Wait until the next day and start over at #2.
7. This cycle repeats a few more times and then, while mowing, the
engine cuts off. Upon inspection, the 15 amp fuse to the PTO has been
blown.

Now, some background. I have discovered that when the key is on but
the engine is not running, I can engage the PTO (with a fresh fuse)
and I can hear the PTO clutch engage. No problem here, however, if I
leave the clutch engaged for about 1-2 minutes, I can feel practically
all the wiring becomming hot. Everthing from the Ignition switch
(key) to the wires coming off of the PTO clutch (these are VERY hot).
I thought heat was involved when I noticed that each of the blown
fuses would have the blue plactic melted on the left side if the fuse.

I have a "Technical Manual" for this mower (Thanks E-bay!) but
apparently I need to know more about electrical ciruits to figure this
one out. I have found in the manual were it gives "PTO Circuit test
points". It shows were to place a volt meter and the "normal"
results. I have tested eveything it lists except for one test that I
don't know how to perform. More on that later.

There is only one test that doesn't give me the "normal" results. It
says that if I test the following I should get the battery voltage (my
meter shows 12.4 between the battery's negative and positive
terminals). I don't quite, in this test my meter shows 11.6 (about
10 other tests do show the battery voltage of 12.4). Here are the
conditions: Trans. in neutral, parking break engaged, PTO disengaged,
ignition switch in RUN position, Meter - on negative battery terminal,
meter + on PTO relay terminal 85. The manual shows "if not normal"
check pur/wht wire and diode. I checked the wire itself and cannot
find anything visually wrong. My big question is what is the "diode"?
Could it be causing my problem? Can a new "diode" fix my problem?

The test that I do not know how to do is one in which the manual says
to test the clutch itself. It says that the normal is "minimun PTO
clutch current draw - 4 amps". I don't know how to measure the
"minimum current draw." It says that if this is over 4 amps to
replace the clutch.

So, my questions are, is my problem the diode in the PTO relay
terminal. or the fact that I can't measure the amperage draw on the
clutch and my clutch is really bad. I have attempted to adjust the
air gap on the clutch, and I think I have it set at the .020 inch gap
as recommended.


I appreciate any help you can offer.

Thanks.
CRR
Little Rock, AR