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318 PTO blows 3A fuse

5K views 13 replies 3 participants last post by  twparker 
#1 ·
I have a 318 with the P218 engine.
Everytime I try to engage the electric front PTO, it blows the 3A fuse.
I haven't seen anything like this in the technical manual.
Any suggestions out there?
Thanks,
Tom
 
#2 ·
Tom,

First, welcome to the WFM site! There are many great folks here with much to share on their experiences with these fine vintage tractors.

If you have the TM1590 technical manual you will find this schematic on page 240-15-5.


Fuse F2 is the 3 amp fuse and it is involved in the TDCM and seat switch interlock circuits, per the following description from the manual:
<font size="-1">When the operator is on the seat and key switch (S1)
is turned to the RUN or START position, current
flows from the positive terminal of battery (G1),
through circuit breaker (F3), to key switch terminal
“B”. The current flows across the switch contacts to
key switch terminal “A”. From terminal “A”, current
flows to fuses (F1 and F2). From fuse (F2), current
flows across the closed contacts of seat switch (S6)
to pin “9” of TDC module connector (X22).

The rest of the theory of operation is found on the page following the schematic where I pulled this quote.

You mentioned that the F2 fuse blows, so look closely at the wiring harness to the seat switch. Since the wires pass under the fender deck and through to the underside of the seat, look for pinched or shorted wires.

Let us know what you find and we can go on from there...good luck!

Chuck
 
#3 ·
Chuck,

Let me begin by saying I have been getting answers to all my problems here for the last 5-6 yrs concerning this great old 318 I have.
I have made many repairs/replacements successfully thanks to this forum.
But this one has me baffled.
A little history.

Starting last year, my PTO started acting up. After it got hot and the PTO was shut off it wouldn't engage. Checked forum and adjusted gap and seemed to work well for awhile.

Then a few days ago while I was mowing, the battery light came on. I was almost done so I kept mowing. After about ten minutes the PTO self disengaged.

I figured that I may need a new PTO, so before I went out and bought a new 300 dollar unit, I decided to remove end inspect the old one.
Some one had replaced the original with a Japanese brand, oguma or something.
The field coil looked good and had about 2.5 ohms resistance. Not great but after reading some posts, enough.
I cleaned up both plates, checked the bearing(which was borderline), cleaned everything up and re-installed and adjusted.
I had the 3A fused holder out at this time as I was waiting to get a new one so I wire-nutted the two together to test the PTO and it worked great.

I also replaced the old battery, which read good but had some very cloudy water in it, with a new Red Top Ultima 34.
I checked the resistance of the stator, 019 right on specs, both regulator specs, right on, replaced both in-line fuse holders w/new fuses and started her up. Ran great. Then hit the PTO switch and immediately blew the 3 amp fuse.

That's where I'm at a loss.
The tech manual says a shorted wire will blow that fuse when you turn the key on and there's no mention of the PTO having any effect on that fuse.
I put a 20 amp fuse in and retried the process and the engine started but the PTO would not engage and the battery light came on.

Also the fuse holder was getting warm.
The manual says this fuse is only to make sure high voltage does not get to the dash lamps. So I'm thinking that is where the problem is.

I have had the fender deck off numerous times and have always made sure the wires were in a good place so I'm very doubtful that is the problem, but will check anyway.

Thanks to all you guys out there.

Tom
 
#7 ·
Tom,

While the PTO coil does get powered from the 20 Amp fuse (F1) the interlock is from the 3 Amp fuse, so the seat wiring is where to start. You should find and fix any bare wires you find -- look for pinched or flattened insulation along the length of the wires. You should restore the safety function provided by the seat switch as well when you are doing this (using a jumper is only recommended for testing purposes and not for operation of the tractor)

A PTO coil resistance of 2.5 ohms translates to an operating current of around 5 amps at normal charging voltages of 12.5v volts and above...might indicate some internal shorting and would be consistent with both the balkiness / failure to engage when hot and the charge light coming on.

The TM1590 has this to say about blowing the 3 Amp fuse in section 240-25-9:
• If the 2 or 3-amp fuse blows each
time the key switch is turned to the
RUN position, a short is probably in
the 2 or 3-amp fuse power circuit or
inside the TDC module. Check red
wire running between fuse and TDC
8-pin connector and pink wire
running between TDC 8-pin
connector and seat switch.
• If sitting on the seat blows this
fuse when the key switch is at the
RUN position, there is probably a
short in the pink wire running
between the seat switch and TDC
2-pin connector or a short may be
inside the TDC module.

MOST LIKELY AREAS TO CHECK FOR
SHORTS:
Wires routed through panels or between frame
and deck.
Wires routed near exhaust manifold or muffler
Wires routed near the drive shaft.


The TDC Module is very expensive and can't be returned to the dealer if it turns out that it is not the failed part, so be sure to test everything else first. The module can be repaired sometimes as well, search the site for "TDCM + diode" or similar search criteria.

Hope this helps...

Chuck

(Message edited by chuckv on July 08, 2008)
 
#8 ·
Tom,

I looked up the Ogura PTO clutch coil spec and it should be 3 to 4 ohms. Yours is definitely beyond the end of recommended 'good' range and may be the root cause of your original issues with pull-in reliability.

These clutches were original equipment on some John Deere tractors (not some cheap replacement...) and are said by many to be the most desirable version. You can replace the winding on these PTO clutches instead of a complete unit replacement, which may save you some money.

Here is the trouble shooting page from the Ogura site:
http://www.ogura-clutch.com/products/pto/troubleshooting/will-not-engage.html

Chuck
 
#10 ·
Tom,

Yes, that 9 volts is not enough to charge the system if the terminal you are reading is the output of the regulator. The other two pins are the AC from the stator, and I don't recall which pin is in the "center" of the part. Since you have a voltmeter handy, what is the voltage across the battery when the engine is running at full governed speed? This needs to be more than 12.7 volts for the charge lamp to go out.

Is the 3 amp fuse still blowing? It only goes to the seat switch and the TDC for the charge lamp control circuit.

Have there been modifications to this harness by a prior owner? Any crossed connections would cause very bizarre behaviour. How long have you had this tractor functioning normally prior to the present problems?

Chuck

(Message edited by chuckv on July 13, 2008)
 
#11 ·
Chuck,
I've owned this machine for at least 5 years and have never had any electrical issues until last year.
After scanning some old posts, some guy named Greg or something said he had a similar problem with his PTO and it was a gradual thing, like mine.
I think I may have fried the regulator myself with neglect in keeping it grounded properly while testing.
I was performing the test of measuring the voltage across the battery this morning and the needle on my tester spiked and then blew the fuse in the tester.
I got the hardware stores last fuse and didn't retry that particular test, but did check the reg output(center pin) and got the 9v reading.
I've checked all the grounds with a continuity tester and all wires seem good.
I even replaced the 25 amp circuit breaker.
After reading some old posts, I believe I should just replace the PTO and regulator.
Some guy named Greg or something said he had a similar problem with his PTO and it was a gradual thing, like mine.

I'm thinking replace the regulator first, then PTO next as maybe it's drawing to much amperage>

Tom
 
#12 ·
Tom,

As mentioned in my posts #1044 and 1045, your reading of 2.5 ohms for the PTO coil resistance is outside of the recommended range from the manufacturer Ogura. Your PTO needs to be replaced for sure if you have had difficulty getting it to engage when warm.

I think that you are referring to the thread by Greg McMahon at:
http://www.wfmachines.com/discus/messages/335/99746.html

Note that he bought just the Ogura coil from Deere and it was about $120. Complete PTO units go for more than that... and since they seem to have a service life of only about 20 years, I would not bother with buying a used one.


Definitely repair and verify the ground connection when you replace the regulator, then move onto the PTO repair / replacement.

Chuck
 
#14 ·
Hey Guys,

I replaced the Regulator and got 14+ DC volts from it. My stator checked out at 48 AC volts.
Same problem.
I checked the PTO switch with the unit running and found that to be heating up also, with some melting to the plug.
Replaced the PTO switch, same result.
Finally, I replaced the big dollar Item, the PTO Clutch itself.
Bingo!
Runs like the tractor I've loved for years!
When I took out the field coil this time there was a pronounced crack in it that wasn't there before.

In summary, I would like to say that in my first attempt at electrical repair, this was a great learning experience thanks to all you out there.
And I hope someone else will benefit from this.

Tom
 
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