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komatsu PC-120-6 no start no power

Diesel Dan 92 · 2020-07-17 13:17

Operator calls this morning says machine is dead. No crank, no power to monitor panel or blower fan anything, etc. Have 23.5 volts at batteries, checked and cleaned connections and grounds in the battery box, no change. Have voltage at hot wire at ignition, shows kinda low, like 16.6v ? Turn key to "on" and voltage goes to zero ? I'm stumped.

Replies12
  1. #1heymccall2020-07-17 13:38

    Main power relay connection, or the relay itself, or, just plain old worn out batteries?

  2. #2Jgm2020-07-17 16:39

    Sounds like a bad battery relay, you can jump it for a temp fix but should be replaced.

  3. #3Diesel Dan 922020-07-18 10:26

    UPDATE: Ran new hot wire to ignition switch. Machine will start and operate but still no power to gauge panel.

  4. #4Jgm2020-07-18 10:41

    You will have no power to monitor or gauge power, if you jump your battery relay then you will, on the battery relay you have 2 big connectors, (they come from battery +/-) 2 smaller ones, if you go from the + to the smaller one with a small jumper wire then it should work. I'm not sure with that model, but by the bigger models they have an extra inline fuse behind your batteries that is connected to the battery relay, which that fuse powers your monitor as well

  5. #5John C.2020-07-18 12:38

    You have an old machine. Have you checked the fuse panel and fuses before doing anything else? It's been quite awhile but they also used to put a fuseable link down stream of the battery disconnect that fed the computers and monitor. It should be just above the battery disconnect and have a plastic flag on it. Is the battery disconnect working or not? If you put your hand on the battery disconnect and have someone in the cab turn on the key, you should feel and hear it snap in. Do you have a service manual and have you done a net search on information about these machines. I know I have posted on this board how the disconnect works and how to fix them.

  6. #6Diesel Dan 922020-07-20 20:39

    The battery disconnect works now that I have run a new hot wire to the ignition. The larger wire on top is direct battery voltage, the red wire is the new one I ran to the ignition. The bottom large wire and bottom small wire get voltage upon turning key to “run” position. The top small wire has continuity to ground. The machine starts, operates and moves as it is now, just nothing out of the gauge / control panel. The three loops above the disconnect are fusible links, they appear to be fine.

  7. #7Diesel Dan 922020-07-21 07:26

    As I understand, the monitor is powered from the smaller wire leaving the disconnect switch once the key is turned to the “run” position?

  8. #8Charles Hudson2023-02-03 06:49

    How similar are the 120 and the 158 ? I have the same issue with a 158. TIA. Charles (Possum)

  9. #9Simon C2023-02-03 22:04

    The connections on that battery solenoid look like they could use some cleaning. Worth checking out. Simon C

  10. #10Simon C2023-02-03 22:05

    The connections on that battery solenoid look like they could use some cleaning. Worth checking out. Simon C

  11. #11Charles Hudson2023-02-04 08:47

    I am really embarrassed as to what the problem was!!!! The fuse block cover was lost years ago by a previous owner. Needless to say it is not the easiest to see in it's location. I diligently removed each fuse and checked them. Now what I didnt notice(I am going to blame it on age and bad eyesight) was that there was a fuse MISSING. The last fuse in the block was not there and I didnt realize it. It had fallen out and was laying in the floor. I took a chance, plugged it in and everything was good. It felt a little loose putting it back in,,,,but not THAT loose. The gremlins are out and about I guess.

  12. #12Dai digger2023-03-27 18:43

    Had similar problem Changed the stereo,and now there’s no power to nothing Wish I’d left it alone now.