DFR System part of machine automation and is for the control of in-feeding crop from the header into the feeder house and then thresher, combine automation allows for variable speed control, (setting adjustments on the go) of the different functions of a combine such as crop feeding, crop threshing, cleaning, etc.
This machine would not react to operator use/input of the toggle switch to increase the DFR speed via electric over hyd solenoid in a hyd manifold / valve stack, the original troubleshooting went in the direction of a no flow thru the manifold.
The main valve was replaced with no improvement, at this point the dealer asked for on site support.
The circuit is comprised of a toggle switch for manual operator control to speed up and slow down the feeder drive, the switch is an input to the armrest control module (acm), the acm communicates via CAN to the universal control module (ucm) which controls the coil on the main valve for increase and decrease of the DFR.
The machine has switch diagnostic capability via the field computer or machine display, the switch diagnostic function indicated there was no issue with the switch input to the acm, this tells us the acm is seeing the input from the operator so the next check was to scope the circuit from the ucm to main valve coil for DFR control.
Heres the wiring diagram for that circuit.
I placed a current clamp and back probed the control side of the circuit, cycled the DFR meaning speed increased then speed decrease.
We could see that the increase function when activated voltage would turn on then turn back of within a few ms, the decrease when activated would stay on as long as toggled on, when the switch was released the voltage would return to approximately zero.
Next was checking the circuit for a short to ground, we found that the harness had continuity between the control side and gnd side of the DFR circuit when checked at the main valve DFR coil, since the circuit had direct path to chassis gnd we then disconnected the chassis ground which eliminated the continuity. The conclusion was the control side of the circuit must have a direct short to the chassis and since there is no fuse protection on this circuit it must be the ucm that is shutting the circuit off.
From this point I placed a call to our second level (L2) support to discuss what we were seeing and what if any additional testing we could perform, L2 was sure we had a harness issue, I was not certain as the turn on and off of the increase command was very similar in pattern to the decrease command.
The decision was made to order a new harness and a new ucm, once the parts arrived the harness was replaced which did not result in it being fixed, the ucm was then replaced which resulted in the correct function of the DFR.
Heres the question I have, had there been a prominent difference in the two patterns that would indicate a issue in the circuit outside the ucm, since the patterns were similar does that indicate it is a problem internal to the ucm?
Thanks for reading, look forward to any comments.
It's always great to see the scope being used outside of the automotive and a combine is always pretty impressive!
I need to digest this and then get back to you on your comments about the UCM. It maybe that another measurement may have revealed the answer.
Thanks again and apologies for only get to back to you know.
Hindsight I would have went that route, we did try using a headlight and taillight in place of the coil/load using all OE wiring, the headlight drew too many amps to light for more than a split second, the taillight would turn on and stay lit... The capture done with the taillight is attached here: