Bill Earl posted a discussion

Hi,I have a suite of ST60 instruments and Smartpilot Controller installed on a sailboat.  The instruments were installed by the prior owner.  They are wired in series as shown in the attached diagram.All of the instruments have worked well for several years, with some minor repairs in February 2012 when one of the Seatalk cables broke.  (The original installer had done a sloppy job and there was an unsupported splice in the cable that eventually broke from strain.)  Anyway, the boat sat for several months this year and when we decided to go for a sail, none of the instruments were working.  They were all blank, as if they had no power.  The first thing I did was to check the input to the Depth instrument (#2, above):  13.79 v and about 9.21 v (max) on the signal line.  Then I checked the output:  it was bouncing around between 1.6 to 4.1 v and there was about 2.5 v (max) on the signal line.  It may be worth noting that when I turn the instruments "ON" at the panel I hear the little beep-beep normally heard when turning them on.  Then I bypassed the Depth instrument by taking the cable off at point #2 and attaching it to point #3.  Then all of the instruments appear to be working since they give "normal" displays for a boat sitting in a marina.  I conclude that the Depth instrument has failed.  However, I don't want to remove it and send it for repair or to spend $300 for a new one only to find that it's working and I've just missed something obvious.  So, my question of the gurus is:  Would one expect an ST60 Depth instrument to fail with low voltage out on the power wires of the Seatalk cable?  Is my interpretation correct or are there some other tests I should be doing?  Can this instrument be repaired or do I have to purchase a new one?  It would probably have to be an ST60+ because that's all I've found for sale at the normal places.  And finally, are there any issues with connecting an ST60+ to the existing transducer?  I haven't physically checked the transducer so I am not sure exactly what is there but I am sure that I don't want to have to change it while the boat is in the water.Sorry for the long winded post but I thought it better to give too much information rather than too little.ThanksBillSee More