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Recent content by NCMilt

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    Komatsu PC75UU1 won't lift boom

    One more
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    Komatsu PC75UU1 won't lift boom

    Here's (a typical) page from the manual with a drawing of the main pumps as well as some pictures.
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    Komatsu PC75UU1 won't lift boom

    I have a manual. Unfortunately, it is mostly drawings and legends. There is no "Theory of Operations" as many other service manuals might have. Troubleshooting doesn't seem to have anticipated my particular problem. There is a procedure using a proprietary tool to test the flow of the piston...
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    Komatsu PC75UU1 won't lift boom

    I'm here because I don't know a lot about this stuff. What is a "closed center"? To be clear on the relief valve, AFAICT, there is one relief valve on each of the 3 valve blocks plus one on the charging pump. I changed the one on the affected valve block. But now that I think about it, I...
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    Komatsu PC75UU1 won't lift boom

    So, what triggers the servo to enable the main pump? This is almost a purely mechanical machine. If a hydraulic line activates the servo on the pump, can I put a pressure gauge on it to prove that it is or isn't getting activated?
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    Komatsu PC75UU1 won't lift boom

    Uffex, you are correct about the affected functions being all on that valve block and therefore the rear pump. I replaced the relief valve due to other issues with a new one from Komatsu. Maybe I can adjust it, but it's probably not the relief valve. I really don't understand why I can move...
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    Komatsu PC75UU1 won't lift boom

    Thanks for looking at it.
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    Komatsu PC75UU1 won't lift boom

    And here is a screen shot of the hydraulic diagram for a PC75-UU1 (at least the manual says it is)
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    Komatsu PC75UU1 won't lift boom

    Call this a restoration project... Suddenly, I can't raise the boom on its own nor move the bucket with any strength. The boom budges, but won't lift. The bucket will move through most of its travel if it has no resistance. Strangely, if I push the stick out, and pull up on the boom, it will...
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