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  • MMDC replaced but didn't fix the problem

    So I just replaced the MMDC 6607-20009-01 last weekend after the end of last season it started spewing water out of the bottom. Before I pulled it out, the tach and fuel gauge wasn't working correctly, now the hour meter doesn't work and the fuel gauge started to work. The tach also did not reset so I am guessing that won't work right either. Does anyone have any idea of where I should start with the troubleshooting?

    I have pulled both batteries and put them on the trickle to top them off. I am unsure where to check the grounds since I really haven't found one. Lastly, everone keeps talking about fuses yet I can't find more than the one on the engine, should I replace that one just to be safe?

    Any help would be helpful.

  • #2
    I'm assuming since you have MDC that these are digital gauges from Medallion. In order to trouble shoot these you have to understand how they work. The gauges are attached via a bus communication network and each gauge has an address. The addresses are used by the MDC to send specific information to each of the gauges that corresponds to their individual purpose. The biggest chink in the armor of this system (and there are many) is that they went cheap and used a poorly implemented bus topology without shielding and even cheaper gauges.

    So what goes wrong.......

    Noise - Electrical noise on the bus is a very typical problem with this system since none of the signal cables (the wires connecting the gauges) are shielded from things like radios, pump circuits or other electronics located in the dash. Electrical noise can cause intermittent or total gauge failure depending how bad the noise is.

    Grounding - MasterCraft suffered through a transition period where the boats simply where not being built to the standard they are now. Bad vinyl, workmanship, substitution of materials and less than stellar electrical systems were common throughout this period. Poor grounding can cause electrical noise, ground potential issues (floating grounds) or open circuits depending on the level of implementation or failure.

    Cheap gauge components / poor system design - This one is all Medallion and all manufactures that bought into this system early suffer the same issues. Since all the (cheap) gauges are on a bus every gauge is subjected to any condition that occurs on the bus. Think of it as a string of pearls. Any force applied to one pearl on the string effects the others. In this case any electrical noise injected either externally or internally, say by a cheap gauge going bad effects all the other gauges and the MDC which are all located on the same bus (string of pearls if you will). This is what makes the system design so poor. If we say gauges are a critical, why would you design a system that can be completely shut down with a single component failure. Worse yet (and it does get worse) trouble shooting this system can be near impossible with intermittent issues without massive replacement of system components.

    So how do you trouble shoot this system. Well there's massive replacement which you've already bought the most expensive component, the MDC. Continuing down the massive replacement path would be a complete set of gauges. This would eliminate the possibility and likelihood that one or more of the gauges is going or is bad and is injecting noise on the bus effecting the other gauges. This wouldn't be a bad path to take but it still does guarantee a fix as you could have external noise or grounding issues.

    Before continuing down the massive replacement path I would recommend going through the electrical system one connection at a time. This is especially true of the ground circuit. All the circuit wires positive and negative will route to bus bars. These bus bars in turn will have larger cables that will go back to the battery. The battery in turn will have a ground wire that will go to the engine block and the connection to the engine block will serve as the primary ground point for the entire circuit. It is important that the entire ground circuit is functioning properly. Failures in this circuit can cause everything from noise in the stereo or in the case of the Medallion gauge design intermittent or complete failure of the system.

    When I went after the intermittent gauge issue I was having on my 03 X2 I removed every ground connection from the bus bar, cleaned and reinstalled them. I replaced the ground run between the ground bus under the dash and the battery with a larger gauge tinned copper cable and clean every connection going all the way back to the battery. After all this I still had issues with my gauges however they didn't occur nearly as often and the hissing in my stereo went away. I was about to replace all the gauges when a deal on my current 07 X2 came along that I just couldn't pass up. So the rest of my gauge issues went away with the boat.

    I've hear of a mythical device that Medallion made that could troubleshoot a failing components that some dealers had but I have never actually seen one. Lastly there is a growing number of boat owners that are tossing the entire system on older boats and replacing them with individual "old school" gauge sets which isn't as hard as it would sound. There was a guy on TT that did this not too long ago that did a complete write up of his installation. If you get feed up with the issue you may want to consider going this route...... Good luck getting this fixed.

    Comment


    • #3
      Sir,

      Thank you for the reply. It was very in-depth and now I understand how it works a lot better. I looked in the forum and couldn't find anything on how to troubleshoot the components/MDC.

      It looks like I will be in the storage (12x12x45) this weekend taking off every ground, cleaning and re-tightening it all down. I am curious on why the hour meter completely went away though. I thought that the info came from the MDC.

      Comment


      • #4
        Is the hour meter separate or part of the tach on your boat? On traditional systems the hour meter is just that a separate clock that runs when the key is on. Not sure how Medallion implemented this with the MDC. I would think it would be a function of the MDC. The ECM on newer engines also logs the hours but you need a scan tool to see of reset this.

        It is very possible you have a bad ground somewhere or a bad positive connection. More likely though you could have a single or couple of bad gauges. When I was trouble shooting mine I disconnected one gauge at a time then would try running the boat to see if the problem cleared up or at least changed. I was about to go the other way with it and connect only one gauge at a time but sold the boat. At least yours sounds constant and should be easy enough to see when the problem changes.

        Comment


        • #5
          So I took off the battery wires and all of the grounds and cleaned them. Now most gauges work. The only gauge I am still having troubles with is the tach. I swapped out the 5-Pin can bus connection on three different areas and connected and they all did the same. I took a video of what it does. Here it is.......

          http://vid1077.photobucket.com/album...psxy7snhox.mp4

          So my question is now, is it the gauge that is bad or is there something I missed?

          Thanks in advance.

          Comment


          • #6
            Considering that the hour meter doesn't come back to life at all and nothing changes when you unplug it I would tend to believe that it's the tack that is bad. That being said this is bus technology and weird things happen when you work with this type of system. The good news is that cleaning everything at least changed the symptom. For $200 I be temped to change my gauge color to silver and buy a complete set....

            http://www.ebay.com/itm/MASTERCRAFT-...629cb0&vxp=mtr

            Comment


            • #7
              Hi, I had very similar electrical gremlins related to the MMDC also. I changed the MMDC, however no improvement. I spent a little time today trouble shooting and found the voltage on the ignition switch to drop to 11.2v when under load (12.2v without), both without the engine running. The Wiring setup on these boats is amateurish at best, lots of connectors in the harness, none of which appear to be well protected from the environment. Result resistance causing a voltage drop.

              I traced the low voltage back to the ignition breaker, however wanting to ensure the fix was foolproof, I ran a new fused positive from the battery direct to the ignition switch, and voila the MMDC started behaving itself again. I also ran a new negative direct to the MMDC to be sure.

              So I now have a spare MMDC If anybody wants to buy it, I'll put it in the classifieds. (I'm in Houston in a fortnight so can courier from there.

              Comment


              • #8
                Originally posted by ac505 View Post
                Hi, I had very similar electrical gremlins related to the MMDC also. I changed the MMDC, however no improvement. I spent a little time today trouble shooting and found the voltage on the ignition switch to drop to 11.2v when under load (12.2v without), both without the engine running. The Wiring setup on these boats is amateurish at best, lots of connectors in the harness, none of which appear to be well protected from the environment. Result resistance causing a voltage drop.

                I traced the low voltage back to the ignition breaker, however wanting to ensure the fix was foolproof, I ran a new fused positive from the battery direct to the ignition switch, and voila the MMDC started behaving itself again. I also ran a new negative direct to the MMDC to be sure.

                So I now have a spare MMDC If anybody wants to buy it, I'll put it in the classifieds. (I'm in Houston in a fortnight so can courier from there.
                Was the ignition breaker the 35 amp in the engine bay?

                Comment

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