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Bobcat 863 - Electrical issues preventing aux usage

LessWhole

Member
Joined
Nov 20, 2021
Messages
14
Location
Idaho
Hi folks!

Hoping you can help me with one (last?) problem on my 863 C-Series: When I engage the aux system, it doesn't work and the light flashes. This is the exact sequence I'm seeing:

  1. Machine on (engine running or not; doesn't appear to matter).
  2. BICS enabled (whether through sitting in the seat, or pressing the override button with the cab up)
  3. Press the aux enable button, once, so the top light (momentary) lights up. At this point, the light is illuminated solidly.
  4. Attempt to actually _use_ the aux attachment with the rocker switch on the right hand control.
  5. Nothing happens (no clicks, no hydraulic pressure, no hoses jumping), but the top light goes out on the panel and the lock light starts flashing
  6. At this point, no button pushing can leave this state. Have to turn the key off & back on to reset it.
According to the service manual, a blinking "detent" light indicates an issue in the rod end solenoid:

GXjeV.png


I opened the cab and found the solenoid coils. These are my observations, in no particular order:
  • The connector seemed to be solid, and was clean on the inside.
  • I removed the connector and tested the coil, as prescribed. Each coil was ~3ohm resistance, nicely inside the service manual's 1-5ohm range.
  • I can reproduce the issue with the cab up (key on, engine off). I don't hear any clicking when the light starts flashing on the panel.
  • Each connector on the harness side has a black and a green wire; the green wire on one of the connectors has a red stripe. Both of these had some insulation scraped off to the bare wire, almost looked deliberate. But those spots weren't touching anything, and even holding them manually the issue still happens
  • The fuses in the back right of the machine are all good, including the PWM and Accessories fuses.
  • Last time we used the aux system, several months ago, was to run a cement mixer attachment. I remember having this same thing happen, where the aux system wouldn't engage. I remember then revving the engine to full throttle, then pushing the button. That let the system enable. I thought it was hitting a pressure relief or something on start and needed full throttle to 'start' the aux system, but now I'm wondering if that was an electrical issue too...
  • With the connectors plugged in as normal, and the machine off, there is electrical conductivity from the bare spots on the green wires to the housings of the coils, as well as between the coil housings. I don't know what to do with that information.
  • With the connectors unplugged, I can turn the key on (engine off), perform the procedure above, and the light doesn't switch to flashing. So it only happens when the coils are plugged in, but the coils test correctly...
I'm at a loss for what to do next. Any suggestions? I'm comfortable working with electricity, just don't really know what I need to be checking to eliminate causes.
 

Lowe.Buuck

Member
Joined
Jul 1, 2017
Messages
15
Location
Lake Elmo, Minnesota, USA
My understanding of the C-Series is the Aux solenoid coils are powered by the Pulse Width Modulator (PWM) controller. On my 763 the PWM controller is bolted to the hull below the drivers left arm.

Did you check if the AUX spools are stuck?

The scraped insulation may be from some attempting to check the power going to the solenoids. I don't know how to accurately check the the output of the PWM module at the solenoids with out an oscilloscope. Maybe someone here will jump in with how you can test the PWM output.
 

LessWhole

Member
Joined
Nov 20, 2021
Messages
14
Location
Idaho
Thanks Lowe.Buuck. How would I check whether the spools are stuck? Don't see anything in the service manual for it. Just unscrew the bolt at the top, remove the solenoid body, and check if the inner rod moves freely?

If this ends up being the PWM controller, I'd rather not replace it right now. I have plans drawn up to make my own switch for the aux ports. Obviously no PWM, but all I need is to angle a blade... I can manage with a simple switch. And obviously no safety features, unless I use the 12V output off the BICS interlock signal going to the PWM to enable it. But it's just me operating it.

How insane is that plan? I know they've only 10V solenoids; I'd have to tap off the fuse block, add enough big resistors to get the voltage drop to 8 or 10V across the solenoid. Not too hard.
 

willie59

Administrator
Joined
Dec 21, 2008
Messages
13,363
Location
Knoxville TN
Occupation
Service Manager
I can't say for certain, but I'm agreeing with Buuck, likely you have a problem with the aux control module. And yes, the solenoid coils are PWM coils. Never tried to rig them up analog so I have no clue if that will work, but I do know if you put 12V on them you'll smoke them. And you won't be able to use the thumb switch as that's a hall effect switch, not analog. The thumb switch sends a hall effect signal to the aux control module, the control module converts that input signal to a PWM output to the aux solenoid coils.
 

LessWhole

Member
Joined
Nov 20, 2021
Messages
14
Location
Idaho
willie59 - can you confirm the impression I've gotten from reading everything I can find about the aux system in the service manual? Here's the page from the manual that details removing the coil and valve, with some surprisingly good pictures compared to the rest of the manual:

YlHpk.jpg


Specifically, this is what I think I understand:

  • The two coils on the top of the 863's control valve each control one 'side' of the aux outputs - one is for the rod base, one for the rod end. So each one controls a port. When I move the PWM lever one direction (when it works...), only one of these valves open.
  • It looks like the solenoid pulls the valve up. Don't see how else it could work.
  • It doesn't look like there's any other solenoid that needs to be actuated to enable the aux system. Except for the BICS valve that must be enabled for lift, tilt, etc. to work anyway. I don't have a BICS problem, so far as I can tell.
So this all leads up to the final question: Suppose I had the machine running, BICS enabled, but never pressed the Aux enable switch. If I could physically reach under the seat and pull on the valve end sticking out of one of the aux solenoids, I believe there would be fluid flow through the aux couplers? And if I pulled on the other one, the reverse flow.

Obviously I can't actually manually pull the valve while the machine is running, and if I could, it'd probably be dangerous. It's only to ask the question and make sure I'm not missing another part of the system that needs to be enabled, powered, etc. And to make sure I understand right that the PWC controller only runs one aux hydraulic valve at a time - this isn't some fancy multi-position valve that needs to be e.g. half-down to allow fluid inflow, so far as I can see.
 

willie59

Administrator
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Dec 21, 2008
Messages
13,363
Location
Knoxville TN
Occupation
Service Manager
The aux solenoid coils control "pilot pressure" to shift the main control valve spool that controls aux hydraulic output from the main control valve. When you work the thumb switch the aux control module sends a PWM signal to the solenoid valves to send proportional controlled hydraulic pilot pressure to shift the aux spool inside the main control valve, located just below the aux solenoids. I'm not sure at this point what is wrong with your machine, haven't wrapped my head around it yet. Light on the aux comes on, then it goes dark, sometimes it works, sometimes no, one side only, a lot to sort out there. And you're correct, no way to manually operate the aux spool inside the main control valve, the only way that spool works is by pilot pressure delivered by the aux solenoid coils.
 

LessWhole

Member
Joined
Nov 20, 2021
Messages
14
Location
Idaho
Awesome, thanks. I'm understanding a bit more now. Last few days have been a huge learning opportunity.

Turns out the "valve" assembly that the solenoid operates is more complex than I thought. I was kind of hoping the entire core of the solenoid moved, and I could just attach a cable to the top, run it into the cab, and yank it manually*... nope. Looks like the external part of the rod is solid, and the actual valve travels inside it. The solenoid manipulates the inside of the valve assembly through the housing.

And a single point of correction on your previous paragraph: Right now it never works, not sometimes. Haven't seen it work since several months ago. My guess at this point is the aux controller. I think it's weird that the lights don't flash an error unless the solenoids are plugged into the connectors. Is it possible one of the solenoid pilot valves is stuck, and the PWM controller can somehow tell the solenoid didn't move?

One thing I haven't tried yet that I should: Swapping the position of the solenoids and/or connectors. Would be interesting to see if the other light blinks when the connectors or solenoids are swapped. Maybe that would indicate a bad coil or stuck valve. I also need to grab some kind of high-amperage 9v power supply and manually check that the coils are working.

*Incredibly dangerous, so it's probably a good thing I can't do this.
 

Lowe.Buuck

Member
Joined
Jul 1, 2017
Messages
15
Location
Lake Elmo, Minnesota, USA
Check your Service Manual for the procedure to test the PWM module.

I have two manuals for older loaders and they both have the procedures to back probe the connectors and the normal voltages for both the inputs and outputs for both intermittent and continuous flow

My manuals list the outputs to the AUX solenoids should be 0 - 6.0 volts.
 

willie59

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Dec 21, 2008
Messages
13,363
Location
Knoxville TN
Occupation
Service Manager
That's the problem with C and F series machines, their on board diagnostics were very elementary, much like OBDI on automotive, generic information at best. The later G series machines were a quantum leap forward concerning diagnostics. With C and F series machines, it required experience with their quirks to troubleshoot them. Yes, swapping the solenoid valves may offer a different result and thereby offer a clue of what might by your problem, but honestly, I don't know
 

LessWhole

Member
Joined
Nov 20, 2021
Messages
14
Location
Idaho
I'm looking at the PWM module section now. I suppose I can use a normal multimeter and the PWM output into the solenoids should get averaged out, so I should see the output changing with the position of the thumb switch. I found the PWM controller today, it's tucked under the left fender in a terrible place. But I guess almost all parts on this are in a terrible place.

I'll run the test procedure for the PWM controller tomorrow and report back.

Thank you so, so much for all your help. Very valuable, even if you can't magically tell what's wrong with a machine a thousand miles away :)
 

LessWhole

Member
Joined
Nov 20, 2021
Messages
14
Location
Idaho
Myself and another EE friend took a weekend to play with this. Most shops wouldn't have the tools necessary to do this kind of work, unfortunately. What we found...

- With the solenoids disconnected, we could put an oscilloscope on the output from the PWM controller and see that it's sending the correct signals.
- With the solenoids connected, it sends the correct signal for a very short period of time and then shuts off (and the light in the panel starts flashing, as before).
- So we decided that the PWM controller is 'good', in that it's sending the right signal, but it can no longer handle the full load of driving the solenoids directly.

With this in mind, we built our own system to 'help' the PWM controller. I'll not post schematics or anything (you should really only be messing with this if you already know how to do it), but the components needed are as follows:

EPT7Y.jpg


This is the experiment setup to verify it works - everything now works as expected, including all the safety interlocks and thumb controller.

Now I just have to package it all up in a nice box.
 
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