I have a 1990 Kubota B20 with a BT650AR backhoe. The AR stands for Auto Return, a nice feature which makes it possible to set the position of the swing on the backhoe and automatically return to the digging position after swinging to the side to dump the load. It is controlled by a "computer", a position sensor on the swing arm and two 12 volt solenoids which open and close valves to the swing cylinders as needed.
My machine has always had a flaky computer which sometimes fails completely, stopping the swing operation from working, or causes the swing operation to move at a snail's pace. I have found over the years that hitting the side of the console where the computer is mounted, brings the swing operation back to life temporarily.
I decided to unmount the computer and tuck it in underneath the console of the footrest plate so I could just tap it to fix the no-swing problem. That worked fine until last week when hitting the computer failed to solve the problem.
I tried to open the computer to see if there was a mechanical relay inside which would operate the swing solenoids, or perhaps a cold solder joint on a circuit board, however, I found that everything inside the steel box was potted with epoxy making it impossible to repair. A new computer costs $865.69 on half a dozen websites.
An alternative would be to remove the solenoids and the valve they control and replace it with a manual valve along with a few hundred dollars worth of miscellaneous parts. Total cost about $650 plus a day's labor.
Now, remember I said that the solenoids were 12 volt? So when the system failed the swing arm was swung all the way to the right and there was no way to move it, or so I thought. I dug up a 12-volt power supply from the basement, capable of delivering the 5 amps required to activate the solenoids and ran a test. Hotwiring the bottom solenoid with 12 volts thru a toggle switch, then starting the Kubota I was able to make the solenoid open and cause the swing arm to move to the center!! I thought to myself, how about using a single pole, double throw momentary toggle switch with 12 volts to the center lug and each of the solenoid wires to the outside lugs, then mounting the switch on the console.
That is exactly what I did and I now have a fully functional backhoe which will never fail to swing again due to a flaky computer. I found the 12-volt wire which is control by the key and wired it to the center lug of the SPDT toggle switch and wired each of the solenoids to the appropriate lugs and wired the ground wire to the other wires on the solenoid. Voila, works like a charm.
I have another vision of wiring the solenoids to a fancier rheostat type SPDT switch so I can apply the 12 volts to the solenoids slowly starting with about 5 volts. This would enable me to move the swing arm slowly if needed. As it is now, the toggle switch applies the full 12 volts to the solenoids, which causes the swing arm to move rapidly. Not too fast but a bit difficult to use if you want to precisely position the backhoe. I now do it by tapping the toggle switch quickly to move the arm is small increments. Perhaps a foot controlled rheostat in the 12-svolt wire??
My machine has always had a flaky computer which sometimes fails completely, stopping the swing operation from working, or causes the swing operation to move at a snail's pace. I have found over the years that hitting the side of the console where the computer is mounted, brings the swing operation back to life temporarily.
I decided to unmount the computer and tuck it in underneath the console of the footrest plate so I could just tap it to fix the no-swing problem. That worked fine until last week when hitting the computer failed to solve the problem.
I tried to open the computer to see if there was a mechanical relay inside which would operate the swing solenoids, or perhaps a cold solder joint on a circuit board, however, I found that everything inside the steel box was potted with epoxy making it impossible to repair. A new computer costs $865.69 on half a dozen websites.
An alternative would be to remove the solenoids and the valve they control and replace it with a manual valve along with a few hundred dollars worth of miscellaneous parts. Total cost about $650 plus a day's labor.
Now, remember I said that the solenoids were 12 volt? So when the system failed the swing arm was swung all the way to the right and there was no way to move it, or so I thought. I dug up a 12-volt power supply from the basement, capable of delivering the 5 amps required to activate the solenoids and ran a test. Hotwiring the bottom solenoid with 12 volts thru a toggle switch, then starting the Kubota I was able to make the solenoid open and cause the swing arm to move to the center!! I thought to myself, how about using a single pole, double throw momentary toggle switch with 12 volts to the center lug and each of the solenoid wires to the outside lugs, then mounting the switch on the console.
That is exactly what I did and I now have a fully functional backhoe which will never fail to swing again due to a flaky computer. I found the 12-volt wire which is control by the key and wired it to the center lug of the SPDT toggle switch and wired each of the solenoids to the appropriate lugs and wired the ground wire to the other wires on the solenoid. Voila, works like a charm.
I have another vision of wiring the solenoids to a fancier rheostat type SPDT switch so I can apply the 12 volts to the solenoids slowly starting with about 5 volts. This would enable me to move the swing arm slowly if needed. As it is now, the toggle switch applies the full 12 volts to the solenoids, which causes the swing arm to move rapidly. Not too fast but a bit difficult to use if you want to precisely position the backhoe. I now do it by tapping the toggle switch quickly to move the arm is small increments. Perhaps a foot controlled rheostat in the 12-svolt wire??
