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Thread: Hitachi EX75UR Fault

  1. #1
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    Hitachi EX75UR Fault

    Now Then..
    I seem to have landed an excavator repair job.. It's a Hitachi EX75UR, imported and repainted orange from what I presume to be the purple colour of the Japanese ones. All the labels on the machine are in Japanese except the fuse box lid which is in English.
    The dipper arm ram loads the engine to retract, however nothing when you try to extend it. The problem I'm sure is electrical in the 'Marccino control', a kind of auto depth control / guidance system. I've found 4 solenoids under the cab, one of which isn't energised, these have the pilot oil running through from the joystick. We now have a machine with the boom stuck right out and some.ground works to do!!
    So, does anyone have any tech publications / info / ideas / experience as to what might be at fault??
    I suspect this machine was built in the 1990s. It has the knuckle boom with 3 sensors mounted at the pivot pins..
    Thanks in advance
    Tt, & co


  2. #2
    Admin Muz's Avatar
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    Assuming the seal pack hasnt come off the end of the rod, it sounds like a stuck spool. I had a Volvo EC70 did this to me (Amongst many other things ). As a result the engine was 'loaded' because the pump was delivering oil at full pressure to the cylinder, which had reached its stroke end,.. so the digger wouldnt start, (or only turned over very slowly) Before I got involved in the job, some muppets had already replaced the battery and a starter motor believing that to be the cause. So this would be my most likely cause, apart from the seal pack problem

    Also Normally with VD pumps, theres often a valve on the pump that returns the swash plate to 'no load' .. if no service is called, ( and when you power off) so .. if the valves are good, you shouldnt be getting any engine loading, but if the plate is stuck on load, and there is a valve or MRV problem you will get the same result. But the fact that the ram is stroked out, suggest my options above.

    Try moving a track, does the load suddenly come off the engine ? Tracks are usually rods or cable operated to the block, so arent related to the spool circuit.
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

  3. #3
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    Now Then..
    The machine starts and runs fine, all other services work correctly. If the seal carrier had come off thr ram would pull out with the weight of the dipper arm. Currently it is fully retracted, I can load the engine if I try to retract it further, if I try to extend it, the machine makes no effort. The auto Marccinio has the 'Ststem fault' light on and buzzer buzzing as if on a flasher unit rather than continuous buzzing..
    I suspect there is a fault within the cab / bucket collision system..

  4. #4
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    Quote Originally Posted by Tractortech View Post
    Now Then..
    The machine starts and runs fine, all other services work correctly. If the seal carrier had come off thr ram would pull out with the weight of the dipper arm. Currently it is fully retracted, I can load the engine if I try to retract it further, if I try to extend it, the machine makes no effort. The auto Marccinio has the 'Ststem fault' light on and buzzer buzzing as if on a flasher unit rather than continuous buzzing..
    I suspect there is a fault within the cab / bucket collision system..
    So the ram is fully in, and the dipper is thrown all the way out ? .. Does it have a hydraulic quick hitch fitted ?
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

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    Nope, no quick hitch and yes, the dipper arm is fully out :-(

  6. #6
    Admin Muz's Avatar
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    Quote Originally Posted by Tractortech View Post
    Nope, no quick hitch and yes, the dipper arm is fully out :-(
    Ok hitches can be a red herring if they are plumbed into a main line .. cause all sorts of gremlins when the internal ram fails, but they are usually on the bucket circuit .. so that leaves us with a stuck valve then, or your electrical problem, so is this some kind of load sensing set up ?
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

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    Now Then..
    It's definitely electrical. I've had it digging for half a day, now it's stopped again..
    I'll check the wiring from the controller to the solenoids this weekend..

  8. #8
    Fabrication Guru +1 v8druid's Avatar
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    Quote Originally Posted by Tractortech View Post
    Now Then..
    It's definitely electrical. I've had it digging for half a day, now it's stopped again..
    I'll check the wiring from the controller to the solenoids this weekend..
    Progress of sorts then ? can you not isolate all the extraneous (as in unwanted/required) shite and bypass it?
    If it's got tracks, wheels, t*ts, or an engine, at some point it's gonna give you trouble!!

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    Now Then

    Yes, I imagine with 4 x 1/4 bsp or whatever thread the hoses are it could be bypassed. However when working correctly it prevents an inexperienced operator digging the cab off as its all part of the digger/bucket collision system..

  10. #10
    Fabrication Guru +1 v8druid's Avatar
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    Quote Originally Posted by Tractortech View Post
    Now Then

    Yes, I imagine with 4 x 1/4 bsp or whatever thread the hoses are it could be bypassed. However when working correctly it prevents an inexperienced operator digging the cab off as its all part of the digger/bucket collision system..
    Could quite easily rip the cab off me 'Drema too and I've no anti-sollision devices on her ...... just don't do it ..... or let anyone likely to, anywhere near the damned thing
    If it's got tracks, wheels, t*ts, or an engine, at some point it's gonna give you trouble!!

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