Snow Plow Controller question

[jerryk]

The snow plow controller in the photo suddenly stopped working.  It gives a "No Receiver" error when its powered up.  I checked the data signal lines that run through L1 and there is no signal.  When I check the resistance between the data+ and data- wires that run through L1 it shows 121 ohms.  Is this normal?  Right now I'm trying to see if the problem is with the controller or on the plow side.  I removed D4 to see if it was at fault and still 121 ohms across data +/-.  I don't know how to test the transceiver U6 other than the enable pin is high and it has power. Just no output signal from CANH and CANL.

Any diagnostic ideas that any of you have would be great.  I'm not familiar with CAN devices and just hoping the help a friend get his plow working.

Thanks in advance - Jerry

[fzabkar]

From the datasheet for U6:

Termination is typically a 120-Ω resistor at each end of the bus. If filtering and stabilization of the common mode
voltage of the bus is desired, then split termination may be used (see Figure 38). Split termination uses two 60-Ω
resistors with a capacitor in the middle of these resistors to ground. Split termination improves the
electromagnetic emissions behavior of the network by eliminating fluctuations in the bus common mode voltages
at the start and end of message transmissions.

I think R36 may be a 120 ohm resistor.

[jerryk]

Sorry about not seeing that.  I am curious how communication is initiated between the Controller in the cab and the receiver box on the plow end.  Does the control box initiate the communication or does the receiver on plow end start the conversation.  I'm just trying to see which device/box needs to be replaced or any testing ideas that anyone might have.  The box on the plow end is potted so no real testing there.  It does send power to the controller.

Jerry

[fzabkar]

I have no CAN bus experience. Hopefully one of the auto guys will have some advice.

[floobydust]

The CANBUS CM choke L1 connects to the field wiring (through GRN, YEL wires) so it should have signal there.
Because you see no activity, that to me implicates a problem with the plow and its CAN wiring, on that end. Measure ohms there with the vehicle off.
If there is a problem with the ground between the plow frame/chassis and this box, CAN transceivers can get damaged. Is this a 12V or 24V system?

Normal to see 120R between (+) and (-) termination resistor R36. Also check resistance from (+) and the (-) to GND.
D4 or U6 can get damaged if there is a problem with the grounding between devices.

Is that water residue near Q9? That style of supercap are known to leak and cause damage to the PCB as well, look at C19 later.

[jerryk]

It's a 12V powered truck.  The controller box is in the cab. It gets it's power from a potted box under the dashboard which is on the plow side.  It only provides 4.65V to the controller box.  As for water around Q9, I don't think so.  There are various places of white reside on this board that look like flux residue from reflow.  I can't see water being an issue here.

As for testing for signal, should the cab controller on power up, transmit signal to the potted box under the dash?  Keep in mind that my test was in at my location, not while the controller was installed in the vehicle.  The error is the same regardless.  The only part that I have tested is the cab controller box.  I have yet to visit his truck.  My assumption is the box under his dash takes a signal from the cab controller box and via the box under the dash, must activate various relays to control the hydraulics on the plow.

Again just trying to ascertain whether the controller box he brought to me to test should output signal from the transceiver chip (attached photo) when hooked up to my lab power supply.  Or does it just listen for communication from that potted box under the dash that actually makes the plow work?

Jerry

[drago462]

Hey there,

It sounds like you're dealing with a snow plow controller issue. The 121-ohm resistance between data+ and data- wires is within the normal range for CAN bus communication.
As for testing, the cab controller should typically transmit a signal to the potted box under the dash when powered up. It's likely that the potted box under the dash plays a crucial role in activating relays for the plow's hydraulics.To diagnose further, you might need to visit your friend's truck and check the communication between the cab controller and the potted box. If there's still no output signal from the transceiver chip in your lab, it could be a problem with the cab controller or its connection to the potted box.

Regards.

[floobydust]

I'm not sure what this system is - a plow (not a snow blower) presumably PTO powered for the hydraulics for blade movement? It's on the truck's SAE J1939 bus. The controller has a real time clock, what is that about.

Usually the vehicle's ECU will accept input requests to tell it there is (PTO) extra engine torque required, to raise idle speed and keep it constant, or ramp up or down engine speed etc.
The controller can also interlock things, so it won't move the blades if vehicle speed is high or it's in gear. It will request some seemingly oddball info from the ECU. There is two-way dialog.

Is the supercap holding voltage OK? I ask because the controller's config might have gotten wiped out if stored there. If you give a make/model # I can look at the setup, if CAN options are there. I also see the 24LC04 EEPROM.

It looks handheld so I would expect the cable to simply wear out or get damaged. #1 suspect before going after the electronics.

[Simon]

The snow plow controller in the photo suddenly stopped working.  It gives a "No Receiver" error when its powered up.  I checked the data signal lines that run through L1 and there is no signal.  When I check the resistance between the data+ and data- wires that run through L1 it shows 121 ohms.  Is this normal?  Right now I'm trying to see if the problem is with the controller or on the plow side.  I removed D4 to see if it was at fault and still 121 ohms across data +/-.  I don't know how to test the transceiver U6 other than the enable pin is high and it has power. Just no output signal from CANH and CANL.

Any diagnostic ideas that any of you have would be great.  I'm not familiar with CAN devices and just hoping the help a friend get his plow working.

Thanks in advance - Jerry

Be warned that many CAN bus systems and especially J1939 (vehicle) are designed to be fail safe. When a device sends a message it expects a single bit time ping acknowledge from any other device that picked up and decoded the message (there is a CRC check to perform). If it does not see this it will retry at intervals and within what could be seconds if it does not get an acknowledge it will go off bus as the assumption is that the device may be faulty rather than that there is no one there and it needs to get off the bus lest it is causing a disruption to other working devices.

As I just found out at my own expense a USB/CAN adapter will not necessarily do this as they afton sit passive on the bus and monitor only. If you want to look at the bus working you best do plugged into the machine it is normally attached to.

[jerryk]

The plow is now working and it's problem was in the wiring on the plow side and not with the controller.  My friend thinks I caused something to happen because after I did my testing and removed/reinstalled the tvs diode D4 the plow controller did work but very slowly.  After a short period of time it gave a "Relay Fault"  , stopped working,  and followed with the original error code "No Reciever".  From there he was able to lift the plow enough to drive it to the dealer.  When he tried to demonstrate the problem the plow suddenly worked perfectly.  I have assured him I did nothing to contribute to it's cure.  The dealer went through all the connections, cleaning them up.  He said it seemed like a low power/bad connection issue  given the slow movement and the "Relay Fault" error that my friend described.

I feel like it's the one that got away.  I was hoping to learn something about CAN in the process.  I'm still not sure why the controller transceiver showed no signal.  I get what Simon is saying but you would think that the part that would just sit there and listen would be the potted controller box under the dash that activates the various relays on the plow.  I have a feeling I'll see this thing again and will test the thing hooked up in the vehicle as suggested.

To answer Floobydust, this is a snowplow mounted on a 3/4 ton pickup.  All of these types of plows are electric over hydraulic.  Newer ones use CAN devices and older ones use analog controlled relays.

Thanks for the help.

Jerry

[Simon]

I'm not familiar with the machine or fully understanding what you are doing. What described is standard J1939 specified behavior and is generally built right into the CAN bus controller hardware. What exactly do you wish to learn about CAN bus?

It has many levels depending on what you are doing. At a basic level the wikipedia article pretty much covers it. What you need to do then is get a couple of boards with can bus on them like say a couple of micro controller dev boards and play with those connected together. Although I have a kvaser CAN bus USB adapter that is real handy when I have a working system and want to snoop on it, unless it gets a valid message it won't show you anything. I am finding testing of my work is better done with a picoscope that can decode CAN bus. With the scope I can see the actual signals and the picoscope software does give some feedback like my missing acknowledge bit from a second device or if the message was valid as there is a hardware CRC check with CAN bus.

After that it is what do you want to run on top of the CAN bus, your own protocol, or one of the many. Automotive runs J1939, this is not to be confused with CAN bus 2.0 standard. the 2.0 standard was created for the hardware so that CAN bus could run the J1939 protocol but they are two very separate things and J1939 is covered by copyrighted standards that need purchasing. Essentially all it is, is a list of the message ID's and what data they hold. The other very popular standard is CAN Open that is rather more complex but is freely available, I am trying to crack this one myself.