I ran my fluid low on a PC50uu2 and the boom quit lifting. I refilled it and tried to bleed by moving the boom, etc and it will go down good but not up. It will lift the machine and then I had to climb down and wait for it to bleed off. Then the boom seemed to work and I worked the curl four or five times then went to the crowd and it quit working. Now it’s back to the boom won’t raise. Where should I start?
I’m going to let it set for the night and try it after church tomorrow. Goodnight all. Thanks in advance for any suggestions.
Think your just going to have to spend time bleeding each cylinder by moving it till all the air goes out.
I just had a thought. I bumped a tree limb near the stick potentiometer just before the problem started. Going down to see if I have a problem there. I remembered that there was a short buzz at times. Crossing my fingers. I’ll report back.
Yeah, the threaded rod to the arm potentiometer was bent. Appeared to have an old bend and a new one. See pic. To add to the puzzle, it appears someone before I got the machine tied the reset wires permanently together and to ground. Second pic. What gives? I need to be able to reset the potentiometer?
I’ve got the rod off to straighten it. Does anyone know the proper adjusted length?
BYW, with the rod off, I wired the potentiometer up and all functions work. (Except safety with it tied off, and the depth and height control of course)
I’m still studying the issue in my manual and I came across this drawing. Comparing the drawing in the manual to my setup, the rod is on the wrong side. See pic. Can anyone tell me if you have one of these machines and how yours is setting?
Good troubleshooting.
For anyone who finds this; there are the same/similar problems discussed in the topic “Komatsu "Four" (safety) System”. At this time I am trying to check out my potentiometers before considering deleting the safety system. The pertinent voltages and resistance ranges are found in the manual if one looks enough. They are in different places.
The potentiometer is contained in this shell: Inside You find this: With the part no. On the back:
I found a similar part no. 7861-92-4130 on eBay for $20. I’m going to see if it checks out for this application. Be back in a week or so. I’m going to tape my override switch on until then.
I could not find a potentiometer part no. 7861-92-4180 for sale online. However, there are some with a very close part number that is used for a PC-200 throttle. The part number is 7861-92-4130. I ordered one from eBay for $20; cheap enough to see if it works. It arrived today. You can see from the picture attached it is very close. Two differences: The harness connector is larger, and more significantly, the shaft is clocked 90 degrees different. I check the range of the resistance, and it checks against the shop manual reference numbers.
I’m planning to put the new potentiometer in tomorrow but I still have not confirmed the correct rotation. Can someone with a PC50 with the Four System snap a picture of yours or just tell me if your lever faces left or right? Here is mine as I found it. Is it the same as yours? In this position it will turn the potentiometer counterclockwise. If on the other side it will turn it clockwise.
I checked the range of the lever that turns the potentiometer when I move the arm full travel each way. Its travel is 90 degrees. I now think the new 4130 potentiometer will work, since it has a 180 degree range. I have switched the connector by splicing the wires and will try to hook it up after dinner this evening. I found the shaft in the 4130 is about 1/8inch too long. I’ll deal with that on a grinder.
Okay; it’s all done and works fine, working in all functions and stopping where it should. One note: I didn’t get the new potentiometer shaft short enough the first go. When I tightened it down, it put pressure on the potentiometer that produced an open circuit. When shortened enough, it bench tested fine and after installed I couldn’t be happier. This unobtainable part was replaced for $26. Lucky I guess on the price but there are more of this part number out there if you need one. Happy digging. PS: If I knew how I would rename this thread to “PC50uu2 potentiometer problem “ but that’s where it ended. I wasn’t that low on hydraulic fluid at all.
Click on the “report” button in the bottom LH corner of the window containing your last message. Make your request and click the report button. An admin will handle it.