Hello Folks I'm new to this forum. I'm John. I'm looking for any help I can get regarding my Komatsu PC28UU-2E. I can't find any manuals out there at all. Nothing. My problem is the arm started moving slow and now the boom is slow going up. Every other function seems normal. I did read about the potentiometers on the arm and boom. But, I cannot find any definite information on how to troubleshoot these potentiometers. Does anyone have a service manual with more info so I can start trying to figure out if they are functional or not. I'm going to start there and follow the wires back to their termination point at the other end. I do not have a operators manual either. I'm wondering/asking if the switch by the ignition key can reset the safety functions. There is a flashing light on the dash with what I believe to be a Japanese symbol for caution. Otherwise the machine works good. Thanks.........John
Owner operator manual I found very helpful PDF.js viewer
Good day John I have a hydraulic schematic for the 25-1 not sure if it is the same, if you can post the correct schematics for your machine will try and help you. Kind regards Uffex
Good day uffex, I do not have a service manual for the PC28UU-2E. I have done some research though. This is a learning experience for me. I read the operator manual I posted a link above. This machine has a safety system that prevents the operator from striking the machine with the bucket. I think it is referred to as the 4 way system. There are potentiometers on the stick and boom that feed to a safety computer called the EPC controller. If the conditions are met, the EPC does not let the operator cause damage by shutting down full operation of the machine. There is a reset switch under my seat, it did not change the slow operation. So, the question is, can it be bypassed? There is an EPC valve on a wiring diagram I found. Next question is, if I pull the wire off the EPC valve will the safety function just go away? Well thats some food for thought isn't it. Any experts out there with answers? Have a great day.
Good day John As a general rule, the boom & arm cut-outs are controlled by "close proximity switch". Three wire connections look like a small cylinder easy to by-pass for trouble shooting. Connecting to a solenoid valve which is of a on off. I suspect you have a pump issue could you post a photo of the pump may help. Kind regards Uffex
Well folks here is how the story goes. I pulled the floor up and played with the 4 solenoid valves under the seat finding that if you take power away from EACH they lose function to the stick, boom and left offset function. The fourth from the front takes away all boom and stick and left offset function. Anyway, I started checking voltage readings at the solenoid valves and they were low at like 9 or 10 volts. Then, I checked the alternator output voltage. Guess what ? The alternator was putting out 11 volts or none I didn't have it tested. The low voltage light on the dash was not on/indicating low voltage. So, I attached my big battery charger to the battery, started the machine and tested the boom speed and stick speed which was slow. Then, I turned on the battery charger with the machine running and YES! The speed of the stick and boom is good again. Go figure. New alternator installed and now at 13 volts I'm good to go again with good stick and boom speed. Not the end of this story. I still have to use it and see what the future of this little beast has to offer...............Thanks So if you have 4 way safety system problems,...........Make shure your alternator is putting out normal voltage. Fix = $93 and alot of BS...............Yanmar alternator part number.......ym119836-77200. Pain in the asz to change also..........Enjoy getting greasy have a nice day.