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Chuck,

I haven't had time to try all of these suggestions just yet but, I did get a chance to pull pin #5 out of the TDCM connector and try it again. Same result as before - heard the PTO engage, then popped the 3A fuse. So, I (yet again 馃槀) chased and visually inspected the small wiring harness all the way from the connector back to the seat switch. Still found no evidence of any bare or damaged areas, unless it's just a failure inside the insulation and is just plain hidden.

Based on your suggestion, it sounds like that might indicate a break inside the seat switch harness somewhere - just one that's hidden inside the insulation and not readily visible?
 

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DCT,

A break in the seat switch harness would not result in the fuse blowing, but a partial or intermittent short would. You might try disconnecting the seat switch harness run entirely and run a short wire from the 3 amp fuse to the X22 pin 9 to see if any thing changes (the charge light will still not go out as there would be no voltage at X23 pin 5...)

Let us know what you discover...

Chuck
 

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You'd be ahead subbing in either a 3 amp breaker or an old style 12v incandescent headlight for the 3 amp fuse. If light is dim...all is well, when light gets bright it's drawing current.
This way you can wiggle wires, try switches, unplug/plug back things etc until light glows bright and find your problem.
The light is a current limiter so as to not damage (overheat) wiring. HTH

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Tom and DCT,

There may be hacks (or failures) in the harness that we have yet to discover... I still can't understand why unplugging the PTO from the harness allows the F2 (3 amp) fuse to remain intact when the PTO function is enabled, yet it gets blown if the PTO is plugged back in under those same conditions. There should be no connection between the two functions.

There may be something failing inside the TDCM -- so lets look at how the internals of that module work. I don't have the exact detail of the internal wiring of this module...just the functional equivalent diagram that Deere provides in the manual, as shown below:
View attachment 280985

The 3 amp fuse (F2) connects directly to the X23 pin 5 via the #500 red wire, then continues on through the seat switch and harness to the X22 pin 9 via the #810 pink wire. These are the only two loads on the F2 fuse, so lets look at what they do once they enter the TDCM.

Pin 5 of connector X23 connects internally to the Battery Discharge Lamp Control block in the TDCM. This block has only two other connections shown, the ground connection on the right side going to X22 pin 10, and the lamp drive connection on the upper left side that goes to X23 pin 1. There might be some components inside this Lamp Control block that draws excessive current from the F2 source -- but it is hard to conceive of what that might be that would be conditional on the PTO coil being connected.

The other load for the F2 circuitry is the X22 pin 9 where the seat switch connects to the Time Delay integrated circuit. That block has a single output connection which goes to the base of transistor B. When transistor B is conducting, it provides a ground connection to relay G and through the diode C to the other relay which enables the ignition when its contacts are closed (connecting the X23 pin 3 -- the 20 amp fuse supply input, to the X23 pin 2 -- the ignition coil and the hour meter.) Relay G is the control for the PTO source voltage, connecting the 20 amp source at X23 pin 5 to X23 pin 4 when closed and providing a voltage source to the front PTO switch at X4 on the #760 blue wire.

The power to the relay G coil comes from either the safety switch path when both PTO switches are OFF via diode E, or once the relay contacts D are latched on, through the connection to the other relay and the X23 pin 3 input from the 20 amp fuse.

Since we cannot know for sure what is inside the two blocks labeled Time Delay IC and Battery Discharge Lamp Control, it is hard to envision what component failures might be at play here that could cause the symptom detailed in this thread.

Swapping out the TDCM for a known good unit would perhaps be helpful, but harness hacks can be a source of causing module failure, and it might be risky to do such a substitution. Certainly you would not want to simply start an expensive parts replacement activity here, as these modules are not returnable to the dealer and now cost about $490 each. :eek:

Chuck
A few weeks ago, my 318 battery indicator light would flicker about an hour into mowing. Found a loose headlight wire, assumed that was the cause. Next time out, same problem - but after flickering for 5 minutes or so, it stayed on and then blew the 3A fuse. Fuse appeared to be original and was so degraded I had to replace the in-line fuse holder. Now, the machine fires and runs fine, but battery light stays on. As soon as I engage the PTO, the blades run for 1-2 seconds, then blows the same 3A fuse. Found a mildly exposed/broken section on the 2-wire PTO harness, replaced that as well as the PTO switch with OEM parts. Still has the same problem. However, if the coil is unplugged, the battery indicator stays on but the fuse does NOT blow when flipping the PTO switch. I get the same result with the engine either running or off. Coil plugged in, fuse blows. Coil unplugged, fuse doesn't blow - but the battery light remains on either way. Searching other WFMachine threads I find this circuit only goes to the seat switch and TCDM - and it's typically a seat switch issue. I did in fact find a loose wire at the switch that I have since reconnected - but the problem persists. If the coil has a short (my current theory), why is the battery indicator still lit up even with the coil unplugged or disengaged? Fender deck and battery tray are both still out and I have looked for any bare or broken wires along every inch that isn't sheathed in the harness - found none and couldn't elicit a reaction by messing with any of the length of harness or connections that might be suspect, including the newly crimped in-line fuse. I'm a mildly (but not overly) intelligent human, just a poor mechanic. Any suggestions from the group?


Here goes I had a problem like this years ago. After looking everywhere I pulled the electric pto and noticed that some of the insulation was worn away. Some one told me to get liquid tape and add to cover the worn area. Put electric pto on when it dryed and it worked. Dont know if this helps but good luck.
 

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A few weeks ago, my 318 battery indicator light would flicker about an hour into mowing. Found a loose headlight wire, assumed that was the cause. Next time out, same problem - but after flickering for 5 minutes or so, it stayed on and then blew the 3A fuse. Fuse appeared to be original and was so degraded I had to replace the in-line fuse holder. Now, the machine fires and runs fine, but battery light stays on. As soon as I engage the PTO, the blades run for 1-2 seconds, then blows the same 3A fuse. Found a mildly exposed/broken section on the 2-wire PTO harness, replaced that as well as the PTO switch with OEM parts. Still has the same problem. However, if the coil is unplugged, the battery indicator stays on but the fuse does NOT blow when flipping the PTO switch. I get the same result with the engine either running or off. Coil plugged in, fuse blows. Coil unplugged, fuse doesn't blow - but the battery light remains on either way. Searching other WFMachine threads I find this circuit only goes to the seat switch and TCDM - and it's typically a seat switch issue. I did in fact find a loose wire at the switch that I have since reconnected - but the problem persists. If the coil has a short (my current theory), why is the battery indicator still lit up even with the coil unplugged or disengaged? Fender deck and battery tray are both still out and I have looked for any bare or broken wires along every inch that isn't sheathed in the harness - found none and couldn't elicit a reaction by messing with any of the length of harness or connections that might be suspect, including the newly crimped in-line fuse. I'm a mildly (but not overly) intelligent human, just a poor mechanic. Any suggestions from the group?
Have you load tested the battery. A cell going bad can cause some of the problems. When I'm trouble shooting electrical problems I start there to know that I have a good battery.
 

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Chuck, do you know or have you heard of anyone who repairs tdcm鈥檚? I have 3 now that have the same problem, no power to the pto. They work perfectly for everything else just no pto power. It sure would be nice to have these working! Thanks
 

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I would be willing to try and repair them. Tom
 
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Temp,

You can take the cover off the TDCM units and look for obvious damage. Often one of the diodes shown below will be open and that causes the PTO relay to not get properly actuated. These diodes can be damaged by getting improper voltage and/or load connections made in the tractor harness -- hence my standard comment on keeping the factory configuration on all wiring and safety systems.
Circuit component Font Electronic component Electronic device Engineering


The diodes are very generic and you can use any equivalent to the 1N4004 or similar -- these are just a few cents each, but finding them locally is a bit harder now that Radio Shack stores are no longer common.

Chuck
 

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Im still after re reading the thread over a few times, leaning to wire connection failure. when replacing original fuse holder. AND a mis adjusted or worn PTO gap setting. OP states he replaced the fuse holder with correct colored wiring and asked if possibility of switched wires on harness or pins... Q1... PTO gap wore causing the low V at PTO? could me the main culprit and the fuse blowing could be the effect... am I mis understanding, but did OP originally state fuse blows when PTO was attached with or without engine running? but only when systen was active.... ie key on? I think the battery light has nothing to do with the issue here, and is simply reporting the problem , not the cause. (I'm learning here as well,) and am anxiously following this thread... I'm older and look at the ROOT problem, I think if not PTO gap it would be in wiring to the PTO. .
 

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Monkey - I think a lot of us are having the same thoughts about possibly the fuse wires getting swapped or something simple that recently changed because DCT mentioned the tractor used to work fine before the fuse blew initially. This fuse question has been asked before and DCT says the wires all match up like you said....still we all scratch our heads. This will be a fun one to keep following and learn from once it's solved.

DCT, you are getting excellent advice from others and I hate to butt in, but Chuck's advice is spot on in testing the inputs to the TDCM. If by chance you are uncomfortable testing for voltage at various pins on the TDCM harness, with everything connected as usual, take the 3A fuse out of the holder, sit on the tractor, start the engine and move the hydrostatic control lever to either forward or backward. In my experience, the engine will die because the TDCM module will think no one is sitting on the seat. If the engine dies, it is highly likely the 3A fuse is located in the correct fuse holder. If the engine does not die, it's time to trace wires, fully charge the battery and then test the inputs to the TDCM. Something is probably miswired, the TDCM has failed or the PTO clutch might be the culprit. Just my two cents but DCT, you have a lot of folks wanting to see you get this problem behind you.
 

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Just want to comment that the PTO gap has nothing to do with the DC voltage impressed upon the PTO winding, and only a marginal effect on the static amperage drawn by the PTO. The air gap in a magnetic circuit does have some influence on the dynamic conditions...see this reference:

Don't worry about all the higher math...these reluctance parameters only apply to stored energy and dynamic performance of a magnetic circuit/solenoid during the instant of change -- not to the steady state conditions of the PTO either on or off.

Chuck
 

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Two things:
1) I would be 100% sure all fuses are the correct amperage and didn't possibly get switched around. Chuck provided the schematic, I would double check that.
Certainly if the 3A is where 20A should be (PTO circuit), it will blow immediately engaging PTO, which is why it DIDN'T blow with PTO coil unplugged.

2) A quality Multimeter! Check battery voltage mower off (good battery as already mentioned should be 12.5 to 12.7 volts. Then at idle (what is it?)...then revved up (what is it?).
Post 8 Chuck's chart gives testing procedure.
Post 12 you said "My cheap, analog multi-meter showed something between 12-13 volts earlier today while the mower was running and the light was on."
Which means you have a charging problem & light is on. You want to see (motor revved) about 13.4 to 14.2 volts (roughly).

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I volunteered also having spent my entire career as an electronic tech. Maybe we can team up on this? Looking at the schematic, it is not rocket science, and the units are not potted. Where are you located fuddyduddy? My profile shows I am in Rockford, IL so you do not need to ask. Tom
 
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I appreciate the help guys!! I don鈥檛 want to hijack the op鈥檚 thread, but I guess I already did (just a little,lol) anyway we鈥檒l figure this out in pm鈥檚 and I鈥檒l start another thread as we progress, ty
 

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Yeah, these threads are not really 'hijacked', it 's more like a stream that meanders and ends up somewhere other than where it started. It's interesting to look back at the first post and go 'Oh yeah, that was the original subject'..
 

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I volunteered also having spent my entire career as an electronic tech. Maybe we can team up on this? Looking at the schematic, it is not rocket science, and the units are not potted. Where are you located fuddyduddy? My profile shows I am in Rockford, IL so you do not need to ask. Tom
I'm in Forest, Va.

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Not sure what constitutes a "high failure rate" since NONE of my several tractors had any issues with the TDCM even though many had high hours. I have determined that MOST of the failures attributed to the TDCM in this forum's archive posts actually have a root cause elsewhere in the harness (and many are from owner "hacking" of the system to bypass safety systems, etc.) It is possible to damage the TDCM internally by jumping/shorting the external leads such that components such as the diodes are overloaded. I have seen only one or two instances where the board components had a real self contained failure, like a relay not working as it should, but again these are rare.

Here is a list of what the external connections to the TDCM are meant to have as inputs and outputs. If you cross the wiring or short to other places then you are likely to cause a failure -- but it does not count as a spontaneous one.

Font Material property Parallel Paper Document


Chuck
 
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