I have a pc120-6 that is having some strange electrical problems. After one of our guys repaired a wire he saw sparking going to the preheater solenoid because he lost the display inside the cab, I have lost my throttle which is a stepper motor as well as my swing. Using swing lock and pump override switches does nothing which also means I can't shut the unit off as it uses the stepper to shut the fuel pump down. The weird thing is that if I disconnect the "key on" wire from the battery solenoid and measure voltage with the key on and then off, I get 24v and 0v. If I hook it up to the solenoid, I get my 24v with key on and 13.6 with the key off. I can't think how it is being back-fed keeping the solenoid energized. If I remove the pump controller fuse the solenoid and key switch act normally. I also have a solenoid to the preheater that is acting the same way. The weird one with this is that if I remove the signal wire for the preheater solenoid I lose my monitor display in the cab. I have tracked back harnesses looking for a problem, cut, melted, etc. with nothing so far. Oh, one more good one I almost forgot, on the fuse panel I checked all the fuses with a meter and what's interesting is that for the lighting fuse, with the key off the lower leg (to device) is open which it should be but if I turn the key on it goes to a short. What the heck? Any ideas are greatly appreciated
I'm thinking you are going to have to take the "repair wire" out and see what happens before going any further. Komatsu uses a bunch of diodes to make current only flow one way in circuits that have solenoids in them. My guess is that one of the diodes is blown, likely from the repair work. The 12 to 24 bolt issue is bothersome because that usually means some bench ape figured he could drop a car radio in the machine and hook directly off one battery. It wouldn't be a problem except they usually ground the 12 volt leg back to the frame which creates a short that the computer reads as the machine still being running. What that also does is cause one battery to not be equal in charge with the other giving you lots of voltage issues when the hot wired battery gets tired. Let us know what you find.
Thanks John. I've found some new information after talking in detail to the operator when the problem occurred. While he was loading a conveyor, he lost his swing and his monitor. They opened the hood and found the control voltage wire for the preheater solenoid arcing against the frame. The wire's insulation was melted off from the solenoid terminal for a couple of inches. He used a butt connector, terminal and about 6" of wire to do the repair. The repair is in plain view as the solenoid is on the top of the engine compartment. Also, the pump control and headlamp fuses were blown. They replaced all of them with correct sized fuses and ran the machine for about 15 minutes when the same thing happened and also when I walked in to find the power to the preheater solenoid smoking. I quickly disconnected the batteries and then everything from my first post comes into play. I was wondering is it possible that if I am only getting 13v on the control of the 24v preheater solenoid, could the coil not fully close the contacts and create heat, then melting the wire? To answer your question there are no radios or add ons on the machine. The only good thing is that I can recreate the problem with the preheater other than I have no throttle control at all now. Ive read a lot of your posts and I appreciate your help with this as I am really at a loss at this point. Thanks - Jeff
I'll have to get to my book and study for a bit on this. One item though is that the heater should only be on when the key switch is in heat or start position. There is a battery wire going to the solenoid and the signal wire from the key switch. You should probably check the key switch for being shorted through. I'll check my book tomorrow for some possibilities.
I got the wiring diagram out from my book and my eyes are watery and sore now. Basically you have a diode mounted in the back boom side corner of the cab. You have to remove the plastic covers over the heater and corners to gain access. You will find a bunch of them taped to the main harness. As I recall they will be gray or blue in color. You are looking for the one that has a tag that says D17. You can cut the tape that holds the connector to the harness and then remove the diode. You check the diode with an analog ohm meter. Touch your ohm meter leads to each leg and note if there is continuity or not. Then reverse the leads and the result should be opposite. In my experience when diodes go bad they short through so you will have continuity both ways. If the diode is good you are probably shorting through the harness. The only way for the heater relay to be in the closed position is when there is voltage on the signal wire. Did you try unhooking the connector with the signal wire to the relay? I used to like these kinds of projects but as I get older, heavier and loose my eyesight more I'm glad to let someone else fight this out. Let us know whet you find.
John, I will check that out. I got my hands on a shop manual but was looking at the wrong serial number schematic and was looking for d07 instead of d17. When i first starting looking for the diodes, i only found two that had four pins. They must be buried in the harness. As far as the heater harness, I did disconnect it but then I lose my monitor completely or it will flash dimly in about 1 second flashes. I tried disconnecting the r1 terminal on the key switch with no change. I can also hear the wiper controller clicking on and off (relay I would guess). I'm not a great mechanic but I can fumble my way through most things but this one is really aggravating me and makes me want to fix it that much more.
John, I got a minute to get in the cab and I found the following diodes: D01 3 wires D13 3 wires D03 4 wires D06 4 wires D26 2 wires I have a manual that is for s/n 49821 and up. My s/n is 61160. Could there be a newer manual I should be referencing or an update. Also, these diodes were taped to the harnesses. Does komatsu hide any in the harnesses? I didn't see any others but will check again.
Found the right manual online. Need to test d03
My book covers different serial numbers but also 60968 up and sometimes they make changes that don't show in the books. At any rate is shows the D03 diode for active mode, swing holding brake and swing holding brake solenoid. I show D06 working for the 2 stage relief solenoid, travel speed solenoid and heater relay. because of all the rest of the issues you are showing I would suggest you take all of them out and test them. I think you might find more than one blown through. Since you have the manual you should be able to narrow down the issues some. Komatsu includes a map section that tells you where all the components are located. The location section in my book starts at 20-112-2. Good Luck!
Thanks John. D06 and the other diodes i've found so far test fine, which is really disappointing. Thought for sure that one would be bad. I'm noticing that c16 harness has some of the other components we are having issues with such as the oil pressure. On the monitor, the battery and oil pressure symbols stay constantly lit and do not flash as noted in the manual. I am going to follow the harness through and look for an issue. Is there a test that i can do to be sure the pump,throttle controller is good? I did pull c01 and test for voltage which it does have 26v. Thanks for your help - Jeff
I re-read your post again and it seems everything started at the blown fuses. I would try disconnecting the connectors for the light switches and trying to turn on the key. I show it a X01 and see what happens. The wiper has a computer processor so you might try disconnecting that also and see if your functions will come back on.
So here's the latest. Pulled all the diodes, checked them all okay. Removed x01, same problem. Disconnected battery, plugged in x01 and d3 (which I had forgotten about, but saw it on the seat and put it in. Everything works fine! Started putting it back together, one step at a time and testing functionality between each step. Bring it out to put back in service to run for a bit, and I was traveling across the yard and I thought I'd check for error codes and I was flipping through the codes and had an e101'102 and 103 come up and then the machine did exactly the same thing as before except no blown fuses. But no override. machine runs, no monitor, and no swing. what the heck? On the drawing is the safety relay just a starter relay but it shows the r wire from the alternator connected to it but I'm not sure why. The only other thing is that my voltage from my alternator r terminal seems high at 30.5 volts. Any thoughts as to what is happening? And could high voltage shut down the controllers but that's what the diodes and fuses are for, correct?
The R terminal is a starter safety function. When key is on and the engine off there should be no voltage there. When the engine is running there will be 24 plus volts on that terminal which feeds over to the starter safety relay and tells the computer the engine is running. When you turn on the key but don't start the engine and the monitor shows an engine oil pressure alarm, that is one key that the alternator is bad. The high voltage is telling you that the computer is protecting itself by shutting off that high voltage. Disconnect the R wire and tape it so that is doesn't short out. Now run the machine and see if the problem goes away. If so, you need an alternator. Good Luck!
The reason you have the13v is a poor ground. Use jumper cables to make temporary ground from starter to machine frame. Then fix the engine ground.
Thanks. I had redone all of the grounds previously thinking that initially was the issue (and they were in poor condition). I will check the voltage at the r terminal with the key on. I think i may have voltage there ( key on, engine off). The oil pressure light is on when the key is on and engine off. Actually I have battery and oil pressure. Just figured that since the engine isn't running it would be normal to have the oil pressure and charging lights on. They both go off when started. Today I started the machine again with no monitor, swing, or throttle, same problem. I disconnected the battery to shut off the battery relay (key off would not shut down battery relay unless you pull the pump controller fuse) and then reconnected it because I had been usually shutting the engine down by hand first so i can hear the relay open. When i reconnected the battery with the engine running, the monitor came on and I had all functionality. Since then I can't get the machine to fail. I don't like saying that I'm not sure why it works... Thanks for all of your help with this one. Jeff
HELP!! have the same machine-even close serial# and the exact same symptoms! I can not find the problem. Some times it will act normal and sometimes it has the problems listed above. I have disconnected every component that I can think of(alternator, each diode, display panel-whic is new, wiper motor, wiper controller, governor control, etc etc. and it still does it. ...any ideas??
Have you checked for any codes on the monitor?
Yes= No codes
Because it is intermittent it sounds like ground or wiring problems.
Found it! Was a bad ground. Group of grounds (4) coming out of the harness behind the batteries. one of which had a bad connection. Now on to the original problem. Low pressure......