Z121 start circuit diode?

cdma_pro

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anyone know where the diode that's in the solenoid circuit is located? suspect it may be bad, preventing the solenoid from fully closing. hoping it's user accessible.

getting the dreaded solenoid clicks but no crank


start diode.JPG
 

Dave_eng

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anyone know where the diode that's in the solenoid circuit is located? suspect it may be bad, preventing the solenoid from fully closing. hoping it's user accessible.

getting the dreaded solenoid clicks but no crank


View attachment 59304
I am not convinced your diagnosis is correct.

Diodes fail open or closed but not a bit closed.

Have you jumped your starter to establish it is completely OK.

Jumping the starter defeats every safety feature on your machine and needs to be done with an abundance of caution. The engine could start with the blades engaged and cut off your feet or worse.

Have someone knowledgeable in the seat.

Starter jump.jpg


When you jump the starter, the engine should crank instantly. If it does not then stop looking for problems in the controls and focus on the basics. Poor cables, repair ends on cables, bad ground to tractor frame......

Dave
 

whitetiger

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If you are hearing a "click", the solenoid is probably working. It has two large posts on it, one has the cable from the battery attached, the other has a cable attached that runs up to the starter. With a test light or voltmeter, check for current at each post with the key in the crank position. You probably won't have any going to the starter, which means the solenoid has failed. We see this quite frequently.
 

lugbolt

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the diode is built into the harness. To answer the question, yes I know where it is located. In order to get to it you have to pull the fuel tank, then remove the wiring harness from the machine and then split it open. When they fail, they just fail and go "open", thus nothing works. No clicks or nothing.

There is a real simple diagnosis procedure for these. If it's clicking you (usually) either have a bad solenoid or a bad brake switch. Brake switch failures were real common; Kubota updated them along with a host of other changes. You "could" install the update kit if you don't have it, but it's a pain in the neck. Kubota no longer pays for it either. How do ya know if you have it? LOok down beside the battery, you'll see the brake switch down there. You may have to wiggle the park brake lever to see it. If you have a metal tab on the front side of the switch you have the updated switch. No metal tab, you have the old style. It's possible to update the switch with the new metal tab but the hole ain't there in the crossmember to bolt it to, so you end up having to take the mower apart to drill a hole. Secondly the switch itself is different and the hole it fits in is a different size. Just get the whole kit. I don't remember the part number. Might be K3011-95300 but I don't remember for sure.

Dave_eng the pic of the starter you posted is incorrect for the Z121. Z121 has a Kohler engine that uses a direct drive starter, actuated by a divorced starter relay (aka solenoid)--like an OLD Ford pickup.
 

cdma_pro

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thanks for the replies. Yes I have jumped the starter with a wrench and the mower strarts and runs fine. I've tested the solenoid it works fine when battery voltage applied directly to the coil. I also put a new solenoid in and still get click no crank. both solenoids test fine on a bench.

I then measured the voltage at the + solenoid coil terminal and get +12V during start attempt. I then measured DC current coming from the +12V solenoid coil terminal --- there I only get 0.5-0.8A, I would expect about 3A to fully engage that solenoid. thus I suspect resistance inline with the solenoid coil + wire.

Relay (5) is closing or the solenoid wouldn't click and the mower wouldn't run when starter jumped. Since relay (5) is closing I conclude the brake switch, motion lever switches, and PTO switch are all fine since they control realy (5).

That leaves the seat switch, diode, and key swtich. I tested the key switch and it works fine, and ohms fine. I have not yet ohmed the seat switch or diode, and those are the only 2 things left other than bad wires.

not sure if I'm missing anything else.
 

GeoHorn

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CDMA.... I believe you have overlooked Item 9, “Starter Relay” ...and I had a similar situation I wrote about only yesterday. The “click” is heard... but the starter-mounted solenoid does not activate. The “click” being heard was my starter relay.
The Genuine Kubota replacement relay costs between $82 and $110 plus freight... but I solved it with a $2 part. Here’s a link to my solution (See Response #6):
 

Dave_eng

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Lugbolt.

Dave_eng the pic of the starter you posted is incorrect for the Z121. Z121 has a Kohler engine that uses a direct drive starter, actuated by a divorced starter relay (aka solenoid)--like an OLD Ford pickup.

Thanks for pointing out the obvious error in my info. Only yesterday I was cautioning another member about using the Ford style solenoid because of of the high current draw the safety switches would be subjected to in the absence of another smaller relay. I should have done my home work before posting the image.

Dave
 

cdma_pro

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CDMA.... I believe you have overlooked Item 9, “Starter Relay” ...and I had a similar situation I wrote about only yesterday. The “click” is heard... but the starter-mounted solenoid does not activate. The “click” being heard was my starter relay.
The Genuine Kubota replacement relay costs between $82 and $110 plus freight... but I solved it with a $2 part. Here’s a link to my solution (See Response #6):
I guess i don't see how relay 9 would have any impact on this. you could take it out and the mower would start fine. it could fail to operate and the mower would start even if the PTO were on and the brake were disengaged. to me it looks like all it does is disable relay 5 if you try to start with the PTO engaged or brake disengaged.

thanks for the link to the alternate realys, I may just replace one or both for the heck of it.
 

GeoHorn

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I guess i don't see how relay 9 would have any impact on this. you could take it out and the mower would start fine. it could fail to operate and the mower would start even if the PTO were on and the brake were disengaged. to me it looks like all it does is disable relay 5 if you try to start with the PTO engaged or brake disengaged.

thanks for the link to the alternate realys, I may just replace one or both for the heck of it.
You know what..??.... I may have misread the schematic. I see there are Two relays labelled “starter relay” and I agree with you now that I’ve studied it more. It does indeed seem to be PTO-related in the start sequence.
Sorry.
 
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cdma_pro

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I still think it's the brake switch.
well once I find the friggin' brake switch and ohm it I'll let you know. but I don't think that's it... realy (5) is closing... so the brake switch must be working or that relay wouldn't close...
 

Dave_eng

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thanks for the replies. Yes I have jumped the starter with a wrench and the mower strarts and runs fine. I've tested the solenoid it works fine when battery voltage applied directly to the coil. I also put a new solenoid in and still get click no crank. both solenoids test fine on a bench.

I then measured the voltage at the + solenoid coil terminal and get +12V during start attempt. I then measured DC current coming from the +12V solenoid coil terminal --- there I only get 0.5-0.8A, I would expect about 3A to fully engage that solenoid. thus I suspect resistance inline with the solenoid coil + wire.

Relay (5) is closing or the solenoid wouldn't click and the mower wouldn't run when starter jumped. Since relay (5) is closing I conclude the brake switch, motion lever switches, and PTO switch are all fine since they control realy (5).

That leaves the seat switch, diode, and key swtich. I tested the key switch and it works fine, and ohms fine. I have not yet ohmed the seat switch or diode, and those are the only 2 things left other than bad wires.

not sure if I'm missing anything else.
If you want to rule out the diode for your piece of mind, wire one in parallel externally using alligator clips.

Here is one I have used and which is readily available to a few $.

Diode for Toro.jpg


The design purpose and use of these "flyback" diodes varies amongst manufacturers.

Some use the diode to absorb high voltage electrical pulses when the magnetic field around a coil of wire suddenly collapses.

The starter solenoid is a large coil of wire not unlike half a transformer. Same for the electric clutch.

When the solenoid is energized, a magnetic field swells up over and outside the coils of wire of the solenoid.

When the power going to the solenoid stops, as when you release the ignition key, this expanded magnetic field collapses around the coils of wire.

This produces a high voltage called back emf for electromotive force.

It is a high voltage and can move back through the wiring damaging other sensitive electrical devices like the coil of your relay.

Manufacturers are now taking steps to drain this damaging energy using a "Flyback Diode."


Below is a situation where Toro uses a diode.

fly back diode explanation.jpg


John Deere makes extensive use of diodes to protect the machine from reverse booster or battery charger connection to the battery.
They use so many the group them in relay sized blocks as shown on the attached page.

The presence of a diode in a Kubota wiring diagram could mean many things. I have not found their manuals to offer much if any explanation.

Dave
 

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GreensvilleJay

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I suspect 'starter relay #5' may be faulty. it's in the ground leg of the starter solenoid #16. ANY resistance there and solenoid won't fully engage.
The fact that you get a 'click' means the diode should be fine.
If you jumper the starter solenoid lug going to the #5 relay, turn key and the starter spins, that proves the #5 relay (or wiring) is faulty.
 
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