On my Komatsu PC40-7, the arm/joysticks stopped working while I was using it. Upon investigation, fuse 2 (10A) was blown and now, whenever I turn the key to on (not even starting the machine), the fuse blows within about 3 seconds. When the machine is on, the track and blade hydraulics work, but the joysticks don't. The notation for the fuse is 'PPC lock solenoid valve, safety relay' Any thoughts on how I should go about diagnosing this? Thanks.
In those three seconds, before it blows, do the controls work at all?
These two solenoids are for the travel speed and ppc lock. One of these two...not sure which, trace hoses and you will know for sure....but could be the ppc solenoid or the wiring to it. Swap the solenoids and the ppc fuse will not blow if it is solenoid. The speed fuse (if it is a different fuse?) will blow but at least you can get some work done in slow speed while ordering new solenoid. You can unplug both solenoids and see if fuse blows first...this will tell ya if it is solenoid or wiring as well. When swapping solenoids, if needed, whatch out for this little pin that can fall out the little hole in the center there. I know a lot of people that pulled these, didn't know there was a pin there, lost it, called me to fix....and they didn't see that it fell out. I think this block is under the floor board under your feet. Been a few years since i worked on one of these. There is also a switch under or behind the lever you move down to unlock handle. This switch usually doesn't short out and blow a fuse but the wires could definately be shorting out there some where. Hope this helps. Let us know what you find so we can learn from your experience. Good Luck! p.s. part number for solenoid is 20T-60-72230
You can also check the solenoids with a ohm meter. Check one and then compare it with the other one. If both are the same you probably have a different problem. What I have found many times when the blow fuses happen is there is a diode blown. Komatsu just loves to put diodes across solenoids and is very good at hiding them is really hard to get to places. As I recall the last time I worked on a 40 the diodes were on the harness either under the seat or just behind it. They are easy to check with a ohm meter. You will have almost no resistance one way checking across the terminals and almost infinite resistance swapping you leads around the other way. When they are blown they usually have no resistance either way. Good Luck!