1993 Carver 390: Intermittent Tachometers

[Somerset]

I have owned a 1993 Carver 390 Aft Cabin for 12 months; it's a great boat. The only problem that I cannot resolve is that the tachometers work only intermittently. Usually only the starboard tachometer is working, but at other times the port one works. Sometimes both work for a while and occasionally neither of them works! The "Sync" display dial follows the tachometers (hard over when one works, accurate when both work).

An electronics guy who has looked at the problem says that the tachometers are driven from the alternators. He suspects that since both port and starboard appear to charge whichever battery set is selected (1 or 2), the tachometer problem may be linked to the alternators "fighting" over which one whould be charging.

Does anyone know of this problem and the solution to it? Can anyone suggest further diagnostics to get to the root cause?

Many thanks!

 

[cmariner32]

He may know electronics, but I think he's way off base sayin the tachs are driven by the alternators. It sounds to me like you have a loose or corroded wire somewhere. If you have carbuerated engines with a distributor and ignition coil, the tachs are driven by the coil. If the sync quits in corelation to the tach, it might be corrosion/loose wire up under the dash-that is the first place to look. If its a teleflex sync, the sender unit is a hockey puck looking device usually mounted under the dash with 3-4 wires runing to it and the tachs. Check all those connections and if good, note the wire colors and check those colors down at the engines to see if any loose or corroded wires there.

 

[pj1475]

I had a similar problem on my 4207...electrician had all kinds of complex ideas as to what it might be. Turns out it was just a bad ground. I have found that sometimes its best to rule out the simple stuff first prior to getting too crazy. good luck

 

[Somerset]

quote:

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Originally posted by cmariner32

If you have carbuerated engines with a distributor and ignition coil, the tachs are driven by the coil.

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Sorry: should have said that I have twin CAT 3116 diesels, so no carbs. Not saying that you're wrong on the rest of it though!

 

[dmunneke]

I have a similiar problem with an 85 3697 only for me the starboard one works only partially. The port one works fine.. The starboard one sometimes shows accurate sometimes it shows 1000 rpm when I can here it running 4000. I'm going to dig into the dash this weekend.