I have a 06 hitachi zaxsi 225 uslc, i bought the machine without a thumb but it had the plumbing for a attachment on it. i installed a thumb last summer and literally just had to connect hoses and it worked, i played around with one of the set screws to adjust pressure so the bucket over powers the thumb but that was it in terms of setup. from there it worked fine. fast forward to now well the other day the thumb stopped working but only one way it will open up but wont close.i have checked voltage at the joystick at the first connection/plug for the switch that controls the thumb, when not operating it reads 11.72v when i press the button to open it i get 22.5v and to close i get 17.58v i assume iam safe to rule out the switch.? with the machine not running but key on and pressing the thumb to open i can hear a momentary buzz from the machine somewhere outside. but only when trying to open the thumb, when trying to close i hear no sound and have no operation of the thumb running or not i also went into the self diagnostic option on the monitor to read attachment values front att. operation shows value of 1 or working, says this even when i dont press the thumb button and doesnt change when i press the thumb button either way att.control pressure: i have a reading of 0 when operating the thumb in either direction, even if i hold the thumb to open you can hear the pump working still no value. a side note not sure if relevant, when parked the thumb will creep down in the course of a couple days iam leaning towards a electrical issue however any input on how to diagnose would be appreciated..
Does it have a switch for hammer mode or thumb mode
Track down the solenoid valve (the thing you hear buzzing) find out which one is working, then jump 24V to the other and the thumb should move. Sounds like a problem in the handle (one of the switches) if its an aftermarket handle like a suregrip you can replace just one of the switches. Because you checking voltage right at the handle? If its the OEM handle in the molded plastic you have to replace the handle. I would suggest replacing it with a suregrip for serviceability. Sometimes theres relays in play after the handle before the solenoid valve too depending on the install.
Also check the wire below the joy stick handle.With the constant bending the wire controling the thumb will harden and break.
It could also be the electric coil on the solenoid valve.