Hello I just picked up an old 753, the BOSS system backlight was blown and I've replaced it, but it doesn't appear to show anything The hours show as dashes and all of the gauges have dots on the left but no bars The machine operates fine Any pointers on how to begin troubleshooting this?
The first few things to check are: 1. The BOSS fuse in the fuse block. 2. Raise the cab and make sure the BOSS controller has not been removed. I seem to recall it is located under the cab behind the operators left shoulder. 3. There are multiple multi-wire connectors on the BOSS controller. Remove each and inspect for corrosion. 4. In that same area, there are a number of ground connections to the chassis. Remove and clean the terminals and brighten the chassis before reinstalling. 5. On the LCD display, check for 5V on pin A. (Pin E should have 12V for the back light) both of these connections are fed with orange wires. Note that the Black wire is ground and the purple wires are the data wires from the controller.
Thanks for that - I checked the fuse and it was bad, replaced but still no readings The BOSS controller was there and I checked the connectors they seemed fine - I could only find one ground in that area, cleaned it up and reattached - I'm going to see if the workshop manual lists the grounds so I can see if I missed any My multimeter died but I will check those pins - I don't think the backlight is the issue as the system does light up briefly when I turn the key, but then it incorrectly reports everything as empty A new finding is that it now operates for 30 seconds or so and then stops running - If I had to guess I'd say its throwing error code 1 but of course I can't see it because the BOSS isnt showing anything I found this thread talking about a similar issue but there was no resolution - I seem to be able move and lift things fine for 30 seconds but then it just stops so not sure what the underlying problem is HeavyEquipmentForums
I concur with your assessment. The fundamental function of the BOSS system is to monitor hydraulic/engine temperatures and pressures. If it determines that a sender is not sending information or if the sensor data is determined to be outside the safe limits, the BOSS controller removes power from the engine shutoff solenoid thus shutting down the engine. To allow the machine to be moved so the fault can be serviced, the controller will allow the engine to be started but limits its run-time to 30 seconds. On the Kubota engines, you can manually open the shutoff and put a wedge behind it to keep it open and the engine running. Years ago, the supplier that made the BOSS components stopped making replacements due to limited demand. I spoke with a dealer and they told me there was a Push-To-Operate conversion kit that they could install in the loader to bypass the BOSS system if BOSS parts were unavailable. To be safe you would want to add a couple replacement gauges to take the place of the BOSS display. According to the manual extract that I attached, dealers used the BOSS diagnostic tool that plugs into the dash connector to determine if a blank display is a problem with the controller or the display. If the diagnostic tool receives a data stream then the BOSS controller is good and the display is bad. The manual extract gives a resistance readings for a four of the senders. You could check those senders on your loader to determine if any of those are bad. If the display is getting 5v, I don't know how you would check if data is being sent to the display. An electronics tech might know a way to determine there is a signal on the data lines. Other than that, you would have to find a dealer that still has a BOSS diagnostic tool. If you remove the BOSS fuse, does your loader still operate without shutting down?
I checked the voltages and they seem all correct, it has about 4.7 (which is higher than it should be per the manual?) on one of the data ports and 0.75 on the other - 12V on pin E and 5V on pin A, perhaps the signal is bad? I will try tracing the loom now that I have the schematics. I removed the fuse and the machine appeared to run for longer, there is obviously an issue with the tilt and lift operation, it has difficulty lifting weight and after emptying the bucket the lift struggled to move at all. I had to "pulse" my foot on the pedal and even then it would only move 1/4in at a time. Even on the way down. Does this point to a rebuild of the control valve? Even with the fuse removed the engine stalled after a few minutes. I checked the rear of the machine and the fuel shut off was still in the run position. Any idea what this means? With the BOSS fuse removed is there anything else that can shut off the machine? The drive belt appears taught, I have yet to check the sensor resistance but I would think that removing BOSS would rule them out...
P.S. are you able to provide any photos from the manual of where the grounds are supposed to be?
Re: Lift and Tilt - could be control valve, pressure relief valve or hydraulic pump. An easy check is to connect a pressure gauge to a flat face connector and plug it into one of the auxiliary lines on the boom. Activate auxiliary hydraulics and use the rocker switch on the right handle to pulse the hydraulics. You should see 3000+ psi on the gauge. I just re-read your post and the boom does not want to move up or DOWN . I would first raise the cab and verify the pedals/linkage is actually moving the control block valves. I would make sure you have oil and pressure at the valve. Does the curl and dump functions have normal speed and force? If the control valve needs new seals, Willie59 did an excellent post on how to accomplish the task. HeavyEquipmentForums Re: Stalling - if the shut-off solenoid is open, you could have a fuel delivery issue. Is the primer bulb collapsed when it quits? Have you changed the fuel filter? Re: Ground Connections - I don't have pictures. I had a couple issues with C-Series BOSS and dealer had me clean those connections. They were in the near the BOSS controller/cab hinge area.
I will see if I can get my hands on a pressure tester, I had a look at the pedals and it appears to be moving the control block valves well for both lift and tilt. My description of the issue was incorrect sorry - here is a better attempt: After leaving the machine for over 24 hours I can start it up and drive, lift and tilt no problems. I lift the boom once and it lifts all the way very easily, I then lower the boom (again no problem) - once it reaches the ground, I lift the boom again, again it lifts but with maybe 10% less speed, I lower it again and it lowers at the lower speed. I do this 6 times, with each time the boom lifts slower and slower until finally it is no longer able to lift at all unless I quickly remove and reapply the lift pedal, when I do this it lifts maybe 1/4" with each reapplication, as if the pressure is not being released? Even with the lift doing this, the tilt remains strong, I am able to lift the machine at any time by tilting - into the ground - I am also able to freely open and close the 4-in-1 once I have enabled auxiliary I do believe this fuel issue may be caused by a bad pick up after reading other people's experiences online. Mine doesn't have a primer bulb so I'm not able to confirm whether it is sucking air - I am considering removing the line from the lift pump and then blowing air into the fuel filler to see if air is getting past the check valve... The previous owner did install an inline filter between the tank and the pump so maybe that is interfering although I doubt it I will attempt to make a video of the lift getting progressively slower once I have left the machine alone long enough for it to right itself.
Here are videos of the issue An update, I took out the the main relief and the port relief but I couldn't see anything wrong with them
I was working with my brother today and told him about your issue. His machine at work had the same problem a few years back. They phoned the Bobcat dealer and the Service Manager told them it is a common problem. There is one of the valves on the main block that get fouled and causes this problem. It is not the directional spool valves. He told them which fitting to remove and clean. My brother did not remember the exact details but did remember it only took about 15 minutes to remove and clean it. The loader has been working fine since.
Thanks for that, when he said main block did he mean the same block with the directional valves? This one? https://gpim-media.dibhids.net/ipc/e2229.gif I'll try taking off any valves that I can get my hands on to inspect, but I've already tried the relief valves and they looked okay by visual inspection