Tachometer gauges not working

Discussion in 'OnBoard Electronics & Controls' started by rovi, Sep 17, 2013.

  1. rovi
    Joined: Jul 2011
    Posts: 59
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: ANTIGUA & BARBUDA

    rovi Junior Member

    Hi all, what could cause the smart craft tachometer gauges to suddenly stop working? Each is connected to an optimax 225 gen2 and was operating normally the previous day and the following day when I started the motors ,nothing came from the gauges, not even the lights.I changed the junction box and they still didn't work, finally i connected the cables directly to the gauges and still nothing, does anyone have the solution to this problem? Thanks to everybody.
     
  2. sdowney717
    Joined: Nov 2010
    Posts: 955
    Likes: 53, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Did you ever get the lights working?
    If not seems like a power loss, such as +12, or -12 vdc to the gauges.
     
  3. rovi
    Joined: Jul 2011
    Posts: 59
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: ANTIGUA & BARBUDA

    rovi Junior Member

    No sir, absolutely nothing on the gauges work and all the connections are still in tact,even the ground if you are wondering.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It's seems unlikely the tach has a fuse inside it, though possibility a diode or resistor has taken a dump. Attach a volt meter to the input leads to the tach and see if you're getting any variations with RPM changes. Of course, this all depends on what type (input) of tach you have.
     
  5. rovi
    Joined: Jul 2011
    Posts: 59
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: ANTIGUA & BARBUDA

    rovi Junior Member

    What bothers me is the fact that both gauges fail when they are independent of each other. They are connected via different harnesses and to different motors, so why should they encounter a common problem at the same time. I'm lost.
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Does the gauge cluster(s) have a resistor? Again, it depends on what type of tach you have. Obviously it's not mechanical, so it's voltage or current sensing. I'm betting on voltage, which may have a separate dropping or ballast resistor on the gauge panel. If these are bridged (can't see why they would be) you can lose both tachs.

    Some simple testing will focus the problem down. The obvious thing to is check continuity on the leads. Check fuses. Maybe bypass the leads and hook directly to the engine. Only two wires are needed for this, the trigger and the ground. Two short alligator clip jumpers will do. Also check the rectifier as well. The easiest way is to start the motor and measure for DC and AC voltage at the battery. If you read AC voltage, the rectifier is spent.
     
  7. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Many of the new systems use an electronic brain and speak NMEA. If you have one you need to speak to a pro to find out whats wrong.
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    They still receive a single Michael, so one would likely still be working, not both failing at once. I'm still betting on the dash panel having a resistor or rectifier on it, specific to the tachs.
     
  9. sharknet
    Joined: Dec 2013
    Posts: 14
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Auckland New Zealand

    sharknet Junior Member

    Hazard a guess?

    Does the Optimax use a sensor (Optical/inductive/ECM whatever) under the cover to generate the tach signal?

    Older OBs used the ignition pulse from the CDI pack, but that's old tech. If everthing has stopped, I would be looking under the cowling.

    Edit. Looking at my book I see the Optimax uses the AC generated from the stator wires to generate the tach pulse. Are your engine(s) charging? (greater than 12.8V at idle at the batteries)

    Grey wire from the tach to the two yellow wires of the stator (alternator)
     

  10. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    What you need is an oscilloscope and someone who can operate it. That can provide the answer in a matter of minutes.
    Without it you will continue to grope around in the dark.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.