Good evening all, I am an independent mobile mechanic, primarily I work on ag equipment and with that, mainly John Deere. Occasionally I do get to work on some other things as well. The area that I live in is heavy in ag. With all that being said, I have a customer that is running a Komatsu PC56-7. He stated having some issues with the key switch being difficult to turn and eventually broke the key off inside of the lock cylinder. So the guy buys a new key switch, takes a video of the wiring to the key switch prior to removing the wires. Wires up the new key switch and now it will not start. The dash lights come on, and you can hear the fuel pump running. I have removed the seat to gain access to the starter and verified that I am not getting voltage to the exciter wire on the starter. I have tried to jump the starter and all it does is just spin, and not crank. So I know the starter needs rebuilt. However, I still am not getting the voltage to the exciter wire. Now even though he made a video of the wires he was not aware that on the bottom of the key switch, the tabs were marked acc, b, c, br1, br2. So it’s still possible that the key switch is wired wrong, but I don’t know what wires would go where. I can’t find a schematic anywhere. I’ve called a few Komatsu dealers and gave them the s/n and model #, hoping they could email me one, but their reply is that it is “grey machine” and they don’t have any information on it. I’m sure there are some safety switches in the circuit, but again I don’t know the layout. So I’m asking for some direction as to where to look, any help is greatly appreciated!
Can you share a picture of the serial number tag?
PC88MR-10 from my shop manual. No idea if it's the same.
PC88MR-8, again, not sure if similar.
This may also help but you would need to translate the labels sorry.
It is highly unlikely that a starter suddenly goes bad because a key is broken off in the ignition switch. Did you jump the starter directly at the starter solenoid? Voltage present is not the same thing as voltage present during current flow. More specifically, if a replacement key-ignition switch is installed resulting in new electrical problems that weren't previously present, I would focus on troubleshooting the last place touched. e.g. was the correct replacement switch installed? Are the terminal connections clean? Could a wire be pulling loose from a crimp-terminal? maybe a fuse blew during switch replacement (doing electrical work without disconnecting the battery) - etc. My PC128 has a small solenoid between the starter's solenoid and key-ignition switch. The idea is that the current to the starter's solenoid is high (relatively speaking) and it will shorten the life of the contacts within the key-switch. If you didn't know the extra solenoid was there, one could easily conclude that their starter was bad after installing a new key-ignition switch. I don't know if the PC56 has a similar setup, but it might. IMHO the Komatsu manuals leave much to be desired. Often times you must flip through several diagrams to put together a wholistic view of the circuit for troubleshooting.
Yeah I was going to say, in my experience usually there are two wires coming off the ‘C’ terminal (crank), one thinner gauge and one thicker. They both go to a relay/solenoid (separate from the starter solenoid on the starter). The thinner gauge is the signal for the external relay/solenoid, thicker gauge is the power wire to the external relay/solenoid. The output of that then goes to the actual starter.
Thank you all for responding and sending wiring schematics!! So just yesterday (6-23-24) I finally made it back out to the machine due to weather and other jobs that I had going. I got the rebuilt starter installed and like magic it fired right up. To answer some of the questions; yes i did jump the starter at the solenoid, yes contacts were/are clean, all wires and crimps looked and felt good. What I didn’t know until I removed the starter was that there were 2 smaller wires going to the solenoid, I was only jumping one of the contacts and checking voltage to that contact that I could see. When jumping the solenoid, it would just spin and not engage the starting motor. Saying all of this the machine is back up and running, thanks again for the replies and help!!
not experienced with this piece of equipment but I have a ditch witch that sounds like the same problem, come to find out my solenoid was bad and the way we found out was that it's got a vacuum actuator that doesn't work, and when I lift it myself it starts like a charm...