Komatsu turntable

Bertrrr · May 23, 2020

I have a Komatsu PC128 that will not rotate , there is no grinding or any noise other than the engine straining to make the turning motion all other hydrolics work fine it just will not rotate , I'm thinking the selector valve is the issue but all other functions respond. I am not very familiar with these machines so any help or suggestions would be great , thanks

mikebramel · May 23, 2020

If the engine is straining..... is the brake releasing

Bls repair · May 23, 2020

Something jammed in the ring and piñon gears?

Bertrrr · May 23, 2020

Not sure about the brake releasing or how to verify, the engine does strain like it's trying to turn the machine, it's the ONLY function that does not work , just cleaned it up with a pressure washer to check for leaks and what not
does it get an electrical signal to function ? or is it a set of hydraulic valves to make it operate ? I do not see a bunch of hydraulic lines running to the joy stick area but it seems to be getting the signal to move being the engine strains when the joy stick is telling it to rotate. I do not think there is anything jammed into the gear area b/c it had been rotating before then was intermittent in the rotating function , thanks for your replies

Cmark · May 23, 2020

It seems fairly clear that the swing brake isn't releasing.
I'm not familiar with this particular machine, but look for a solenoid valve on the swing motor not getting current, or maybe a small diameter hydraulic line going off to a manifold somewhere with the solenoid.

Bertrrr · May 23, 2020

Thanks for the input , this makes sense to me , now to figure out where the solenoid valve is and why it is not getting the signal

tool_king · May 23, 2020

Bertrrr said:
Thanks for the input , this makes sense to me , now to figure out where the solenoid valve is and why it is not getting the signal

What dash number is it ?

John C. · May 24, 2020

It's a zero tail swing machine so everything is packed in tight and usually hard to see and harder to get at.
The swing brake is controlled from the computer. The brake is on all the time when nothing is being used. When a function is used a pressure switch for that function closes sending a signal to the computer which grounds the circuit for the swing brake solenoid which operates a pilot valve to release the swing brake. When everything stops the computer waits for approximately seven seconds and the sets the brake again. I believe you stated in another thread that the wiring is all torn up on this machine so I would suggest your problem is there. You can find the solenoid by following the small hydraulic hose connected to the base of the swing motor back to the solenoid block. You should see a stack of four solenoid coils on that block. From that point you can check the wires and harness.
Time to get dirty.

Bertrrr · May 24, 2020

thanks so much for the input, I will try and locate everything this week and figure out where the problem is will update when I know something else or have another question

Bertrrr · May 24, 2020

I found what I think is the swing motor / brake solenoids , planning on jumping 12 volts to each and see if it will allow the machine to swing , not sure if it needs 12 or 24 volts though

Cmark · May 24, 2020

There's no guarantee that it's either 12 or 24v. If it's controlled by a computer it could be as low as 8v or it could be PWM operated. If there is nothing written on the coil indicating its voltage, apply battery voltage to it very briefly to see if the brake releases. If it does, you've proved that the fault is either in the computer or wiring and proceed from there. If you wire it permanently to the battery, you risk burning it out.

John C. · May 24, 2020

You will need to supply a serial number or at least a Dash series of the model number. It will read PC128-?. All the Komatsu excavators I've worked on were 24 volt. You can check the coil with an ohm meter. They run about 7 ohms normally. They are bad when they read zero or infinite. Coil wires hook to the wiring harness with a connector that will have a number tag on it.

Bertrrr · May 24, 2020

Think it reads PC 128-UU , this machine has been neglected and rigged 7 ways from Sunday so it's a jigsaw puzzle at this point, thanks again for your input guys , will update tomorrow after I run some tests on the solenoids

Bertrrr · May 25, 2020

These 2 pics show a number of solenoids that I assume have to do with the swing brake,
can you guys help identify this group ? none have any wiring connected at this point, I did apply 24 vts to one of them and it clicks like it's activating , thanks in advance

John C. · May 25, 2020

The purple paint tells me the machine is a gray market machine. There were four solenoids on standard machines. They were for two speed travel, swing brake, CO cancel and arm half flow as I recall. The first generation machines had some big differences though so I can't be sure of what is in yours. I don't recall there being two different manifolds for the pilot system either.
If you can feel the solenoid click, it is OK.

Bertrrr · May 25, 2020

one of them clicks , none of the other ones make any noise , checking voltage on the wiring that goes to this group, there is about 20 vts when the machine is running , I touched each one off with 24 volts but didn't seem to have any effect. Can you identify the two solenoids on the top near the swing motor ? I haven't tried those yet

John C. · May 25, 2020

Best I can tell you for identification is the follow the hoses to the components.

Bertrrr · May 26, 2020

Well I got the turntable brake to release , jumped 24 volts to the solenoid that feeds the small hyd line towards the swing motor, I'm planning on installing a Toggle switch to engage / disengage as needed for the swing brake so it only sees voltage to the solenoid when the operator chooses to use the brake or not, only concern is the voltage would be present 99 % of the time while operating but I suppose that is the design anyway so should not be a problem , let me know your thoughts guys , thanks for the help

Komatsu turntable

Bertrrr

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mikebramel

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Bls repair

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Cmark

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tool_king

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