Komatsu pc28 cab limit problem

[Jay43]

I have a 1996 pc28-uu-2e. 4081 hrs. Great machine. My cab smashing prevention system is the source of my problem I'm having. The potentiometer on the stick has been a constant problem so I had disconnected the mechanical linkage to it and left it in a neutral position so the alarm wouldn't go off. Now it has failed completely. I removed it and checked it on ohm setting on meter. Has a 1/16 turn area its reading 8-100 ohms then just maxed out and says oh. I have removed the momentary toggle switch for the bypass and installed a on off switch so I can shut up the annoying alarm but light still flashes. It runs great but hydraulics seem to be a bit slower in bypass/limp mode due to the alarm. My big question is can this system be deleted instead of throwing money at sensors I don't need or want. There's only 3 wires.. Can't be too hard.. Red, white, black, on potentiometer.. Red reads 4-5 volts others have nothing.

 

[heymccall]

You'd have to plumb around the pilot solenoids that the protection system controls.

As you've pointed out, the potentiometers are easy to evaluate. Why not test them and replace the bad one(s)?

 

[Jay43]

So there's no way to bypass it electrically? What should they ohm out at? I just ordered a new potentiometer so just curious for future options.

 

[heymccall]

Been awhile. I can't remember if leaving the reset wires together will give a full override without restrictions or not.
The potentiometer, especially a suspect one, can be disassembled and inspected. On mine, the contact fingers would wear out.
I pulled this from a PC228USLC-1 book. My PC128UU-2 is the same.
Can't recall the resistance values.

 

[Jay43]

My pc28 is a baby and doesn't have the display or any code type retrieval. Potentiometer is a sealed unit so non rebuildable. Hopefully my $90 plus 40 for s&h solves my problem.

 

[postmortem_42]

So there's no way to bypass it electrically? What should they ohm out at? I just ordered a new potentiometer so just curious for future options.

You cant bypass the aluminum valve body as others state. This valve body that solenoids are connected to regulates pressure from the PCP and bypassing will either burn out your PCP if it lasts that long or blow hoses on both the feed and return sides going to your pilot controls. I learned more about this system than I wanted after messing with it. The solenoids get 12V usually, and when the potentiometer hits a certain setting, it will shut down solenoids (one for boom, one for stick and one for offset, the fourth solenoid holds open the feed from the PCP and is switched on with key, other solenoids powered by computer or by momentary switch in ON position). You have 2 choices, either wire up all 4 solenoids with 12V full time or modify your plungers on solenoids to push spool valves to open position when bolted in place. There should be no slower operation of controls, unless somehow the computer is regulating voltage to solenoids causing them to not plunge out all the way. PM me if you need more information.