DK40HST Won't Start.

[k0ua]

In looking at circuit diagrams, I notice the HST ROPS tractors have the series and parallel diodes whereas the Cab model just has the parallel diode. I wonder why that is so? No wonder I don't understand these diagrams!

My Diagram shows both models have both diodes. The series diode is biased to allow a "low" to be thrown by the Cruise module so that current will flow in the Start relay coil. Follow the circled 16 connection point over to the cruise module. Just exactly why the series diode is there, I am not certain. It may help protect the cruise module from spikes but I am just not sure.

 

[kco]

My Diagram shows both models have both diodes. The series diode is biased to allow a "low" to be thrown by the Cruise module so that current will flow in the Start relay coil. Follow the circled 16 connection point over to the cruise module. Just exactly why the series diode is there, I am not certain. It may help protect the cruise module from spikes but I am just not sure.

I think you meant to say parallel or suppression diode, K0ua. That's what I thought after reading your response mentioning the two diodes. My reading about suppression diodes said as you state, it is to protect the circuit from high voltages when voltage is removed from the relay coil. Therefore, I think it is likely the series one is what stopped it from starting.

Here are partial scans for the two overall drawings for the ROPS and CAB models where it seems to omit the series diode for the cab model:

View attachment HST_CAB.pdf View attachment HST_ROPS.pdf

It also changes the number for the cab to 14 from the HST's 16, but they both end at the same function on the cruise module.

 

[k0ua]

I think you meant to say parallel or suppression diode, K0ua. That's what I thought after reading your response mentioning the two diodes. My reading about suppression diodes said as you state, it is to protect the circuit from high voltages when voltage is removed from the relay coil. Therefore, I think it is likely the series one is what stopped it from starting.

Here are partial scans for the two overall drawings for the ROPS and CAB models where it seems to omit the series diode for the cab model:

View attachment 421434 View attachment 421435

It also changes the number for the cab to 14 from the HST's 16, but they both end at the same function on the cruise module.

Isn't that interesting. Your Cabin diagram is different.. Mine isn't.. It also shows the series diode just like the ROPS model. I understand the paralled diode to the coil, for spike suppression, but the series blocking diode, I am not sure why it is there. Also not sure why your diagram is different than mine.:confused3:

 

[Nick61]

Ok, I picked up my tractor on Friday. I forgot what it feels like to have a tractor that starts with the key and not a jumper wire. The Diode that they replaced works. They also gave me a spare just in case something is causing the diode to fail. Cross my fingers....

Nick