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Thread: EX 120-3 Electrical Problems

  1. #1
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    EX 120-3 Electrical Problems

    Hi I am new to the site.And was looking for some advice.I have an EX 120-3 and it suddenly stoped and engine cut out.We were sure it was diesel problems, but the diesel system is working fine.The ignition is now trying to start the machine in stage 2 ignition, which is when the machine should be doing its pre checks before, the heater plug lights go out, and then you proceed to stage 3 and machine would start normalyThe machine turns over and over, but will not start or even give an indication that it wants to fire up.Any ideas as to what is causing this and not allowing the machine to start.Any help greatfully appreciated.
    Thanks Pat

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    Senior Member spitzair's Avatar
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    I think something in your shutdown system has failed. I don't know where all the pieces are on a 120-3 but in the EX 100-2 manual it says the following : "The engine is stopped using the key switch. Moving the key switch to the OFF position causes the E.C. motor to return the governor lever to the stop position, restricting the flow of fuel to the engine below the amount necessary to maintain operation. In addition, the emergency relay is activated, which in turn activates the stop motor, cutting off the fuel flow to the engine." I'd start by trying to manually move the governor lever while somebody cranks the engine and see if that helps. If it does then you can trace the problem further. Hope this helps!

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    RE mail

    Quote Originally Posted by spitzair View Post
    I think something in your shutdown system has failed. I don't know where all the pieces are on a 120-3 but in the EX 100-2 manual it says the following : "The engine is stopped using the key switch. Moving the key switch to the OFF position causes the E.C. motor to return the governor lever to the stop position, restricting the flow of fuel to the engine below the amount necessary to maintain operation. In addition, the emergency relay is activated, which in turn activates the stop motor, cutting off the fuel flow to the engine." I'd start by trying to manually move the governor lever while somebody cranks the engine and see if that helps. If it does then you can trace the problem further. Hope this helps!
    Hi And thanks for replying to my call for help.I dont know what the Governor is i guess that is what we here in Ireland call a solenoid.Maybe i am wrong.It is taking a live feed from somewhere either the wires are bared or shorting or the ignition switch or the starter relay are gone faulty.Does it say anything about these problems in the EX 100 manual.Or have you ever encountered this.Thanks again Pat

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    it might have a fuel shut off solenoid. if it does you could try to disconnect the linkage connected to it and hold it open then try and start it. does the ignition work how it should? you made it sorta sound like its not working properly? does the motor turn over and just not start?

  5. #5
    Senior Member spitzair's Avatar
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    Not exactly sure how much this will help you but it's what I found in my manual for the 100-2... I would imagine yours to be similar. I've circled the governor control lever in red, you'll want to find this and disconnect the cable on it, then manually move it and see if the machine starts. If it does, then the problem is somewhere in the electrical side of things, if not, then it's a fuel issue. Actually before you disconnect anything, have someone sit in the cab and turn the key on to see if it moves... If it doesn't move, then go ahead with disconnecting and manually moving the lever... Hope this helps...
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    if your in the cab you should hear the fuel solenoid click as you turn the ignition on. thats probably the easiest place to start.

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    Hi And thanks Spitzair and Eric12. The ignition was faulty and a new one fitted today.When you turn it on to stage 2 the machine starts to turn over which should not happen till one turns the Key fully clockwise, and the key is then released back to stage to when the dump relay and surge relays open to energise the circuit.I disconnected the starter solenoid to see if it was faulty and the machine still tries to turn over but no start,I disconnected the main lead to starter, reconnected it and the problem disappeared all but temporarily.I crossed the the connections got the machine started while also holding the throtle control lever open but the machine had no power to and woulld not run correctly and barly had power to track or move the dipper and boom.It has me totaly stumped.It is electrical but where do i start?Thanks again for the replys guys it is of great help, will get to the bottom of it i know but it is frustrating.Thanks again Pat

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    How do you know the ignition was bad? If the problem isn't solved with a new ignition maybe that wasn't the problem? Also are any fuses popped? Look around the wiring harness near the starter where you moved it last time to see if you have a short or broken wire. I had a similar problem with an excavator on and off for a year, I replaced the ignition and it got better then didn't work again and it turned out to be a broken wire.

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    Hi eric12.I checked the ignition it has been faulty for a while, so had to replace it anyway and was sure it was part of the problem but unfortunatley not.Its a head scratcher this one Thanks Pat

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    So the starter runs with the small wires to it disconected ?

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    hi rtccw37 i am in cork heres my number 086 8293385 give me a shout ,kevin spillane

  12. #12
    Senior Member spitzair's Avatar
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    I think there's a diode in your alternator circuit somewhere that is supposed to allow power to the starter when the engine isn't running and then stops/opens the circuit when it's generating power, ie the engine is running. This is supposed to keep you from engaging the starter with the engine running. I'm not sure if your machine has this but I've heard of it on other hitachi machines of the era, perhaps your diode is fried allowing current to the starter making it run as soon as you turn your ignition on... I'll root around in the wiring diagram of the 200-2 (only one I have) and see if there's one in there... Hope you're making some progress.

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    Hi spitzair, Thanks for all the help.I have got to the bottom of the problem i think,The solenoid has gone faulty and was staying on continuously.Usualy they dont engage, they usualy close and wont engage the starter, but mine has stayed engaged all the time, so it would not start the machine, because the computer and diode were not able to recognise, that the solenoid was faulty the diode would not create the open circuit, allowing the ECU and Throtle to engage the machine would not start.It is a failsafe on the machine to stop the starter from getting burnt out if the solenoid or diodes got faulty and keep trying to start the starter thus causing failure.Thanks once again Pat

  14. #14
    Senior Member spitzair's Avatar
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    Quote Originally Posted by rtcw37 View Post
    Hi spitzair, Thanks for all the help.I have got to the bottom of the problem i think,The solenoid has gone faulty and was staying on continuously.Usualy they dont engage, they usualy close and wont engage the starter, but mine has stayed engaged all the time, so it would not start the machine, because the computer and diode were not able to recognise, that the solenoid was faulty the diode would not create the open circuit, allowing the ECU and Throtle to engage the machine would not start.It is a failsafe on the machine to stop the starter from getting burnt out if the solenoid or diodes got faulty and keep trying to start the starter thus causing failure.Thanks once again Pat
    Hey anytime, that's what we're here for! Glad you got it fixed. And thanks for posting what the problem was, I'm sure it'll help others with the same problem at some point...

  15. #15
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    HI spitzair, thanks again.The Hitachi EX120-3s give alot of trouble compared to the dash 1 and 5.The 2,3and 4s were only half the machines of the 1 and 5 but i had to discover this after i purchased my dash 3. I have encountered alot of problems so if anyone has problems with them i might be able to help from experience.Regards to you all it is a great site and keep up all the good work.Thanks Pat

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