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Old 05-20-2015, 11:23 PM   #1
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motorola tach problem

Ahoy. I'm a new member with a vexing problem. I have a 1978 CHB with two Motorola tachs. They are linked, when one has a problem they both have a problem. Currently they work intermittently, wavering sometimes and not working at all sometimes. I have a fairly new Balmar alternator and regulator. The tachs have always had a slight intermittent flutter but did not stop working until just recently. I've checked all the connections on the lower tach but not the upper one. Any ideas? Jeff
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Old 05-21-2015, 06:00 AM   #2
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FIRST, let me welcome you to the forum...I can't help you with your problem, but, you might want to post it in the "Electrical and Electronics" forum or "General Maintenance Forum" more of our technical gurus are liable to see it that way. Good Luck!
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Old 05-21-2015, 06:10 AM   #3
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Greetings,
Welcome aboard. I have exactly the same problem with my stb'd tach' (Balmar alternator-port is fine) although I don't think they are interconnected/linked. The tach' (stb'd) will register for the first 2 hours, or so then die but sometimes comes back to "life" for brief periods (on and off every couple of hours or so).
My suspicion is one of two scenarios: The tach is getting too hot and shutting down for self preservation OR the battery banks being charged by that tach' are reaching full charge and "something" in the electronic voltage regulator is calling for the tach' to shut down. Bit of a frustrating problem that I've lived with up to this point. Oh, the port tach' is not registering hours so I'm guessing the internal drive gear is probably gone. As far as I know, new gears are unobtainable.
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Old 05-21-2015, 08:53 AM   #4
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Wow! Thanks for the quick replies. I will re-post in the Electronics forum. I referred to this website quite frequently before I bought my boat and it was very helpful. I am impressed with the quality of this website but most impressed by the forum community. Thanks for having me. Also RTF, I've found several sites online for companies that restore vintage instruments. It is possible they might be able to repair yours, but for how much $$$? I think I could live with one meter and log any adjustments needed for the other. Thanks again. Jeff
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Old 05-21-2015, 09:18 AM   #5
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motorola tach problem

Hi. I'm a newbie and am having trouble with my tachs. I previously posted to the general forum but was advised that this forum would be more specific, but if you've seen this before, forgive me. I have a single engine with tachs at two stations. They are linked in that if one has a problem, both have a problem. When I bought the boat a year ago they worked fine. Recently they started to fluctuate. I checked when the engine was running and they both acted the same. Now they will fluctuate, sometimes quit working and then start working again. I do not depend on them to be accurate at all. When I start up they both register "0" at idle. As I increase revs they jump up to around 1200 and fluctuate. They may then hold steady, but as I said I don't depend on them. I have a fairly new Balmar alternator and regulator. I've checked for loose wires at the stater and on the lower helm tach and found nothing. Is there a way to determine if the tach(s) have a problem or if the wiring may be at fault? My next thought is to pull both tachs and have them tested but I really don't want to do that. Thanks for any light you can shine on this. Jeff
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Old 05-21-2015, 11:48 AM   #6
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Greetings,
Mr. j. Ahhhh....single with two tachs. I misunderstood as twins with both tachs (port and stb'd) being affected at the same time. OK. You are most assuredly losing signal from the alternator. Concentrate on THAT as the tachs are probably just fine. I have to give my stb'd throttle a "blip" occasionally on start-up for any revs to be registered on that tach. No fluctuation after the "blip".
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Old 05-21-2015, 02:48 PM   #7
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I had the same problem with my single with dual station tachs. My tachs are not alternator driven but have a sender on the time gear (Volvo). My problem was loose and corroded connectors on the sender. Cleaned and tightened the connectors. Both now work.
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Old 05-22-2015, 12:24 AM   #8
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Alright, it looks like I may have a less complicated problem than I thought. The tachs are activated by the stater on the alternator. Do you know how I could check that out? I will just keep going from that point.
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Old 05-22-2015, 12:35 PM   #9
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If your alternator is providing charge current then the stator is working. As has been mentioned, since both are going out it is almost surely an alternator problem (the alternator itself is going out) or if the alternator is putting out charge current when the tachs are off, then a connection problem.

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Old 05-22-2015, 04:25 PM   #10
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Usually once the batteries are fully charged the alternator regulator cuts back and there is not enough signal to drive the tachs. Next time it happens turn on some DC loads and see if they start registering again.


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Old 05-22-2015, 04:38 PM   #11
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Greetings,
Mr. BH. "...not enough signal..." THAT'S one of the causes for my failure that I suspected. I have, what I vaguely remember, as a 100 amp. Balmar driven by a single belt (I'm not on the boat right now). I can't say HOW my charging system is set up as the vessel is a 1979 with the resultant OP wiring "alterations" in place and I really don't fiddle with the battery switches or settings because everything seems to work and I don't want to inadvertently turn the wrong thing off.
Yes, yes, sorting out the wiring and charging system IS on the "list" but...
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Old 05-22-2015, 08:17 PM   #12
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Yes! my latest theory is that the alternator does not signal the tachs when the batteries are fully charged. My reasoning is that the tachs work when I first fire the boat up, waver after awhile and then shut down. I don't know what the fix is. As I said the alternator is fairy new (out of warranty though) so I hope it can be repaired. Thanks for the help. Jeff
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Old 05-22-2015, 08:28 PM   #13
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Read post #10. Suspect your answer is there. Put some dc loads on, like lights. See if tachs wake up.

If running gennie, turn off charger.
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Old 05-22-2015, 08:33 PM   #14
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Some of the Balmar smart regulators, maybe all, have a special output to drive the tach so that even when the regulator shuts down the alternator there is still a signal to drive the tach.


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Old 05-22-2015, 08:43 PM   #15
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This thread makes me glad I've a single engine and single tachometer. Tach is working fine! (now at 450+ hours). Twice the stuff equals at least twice (if not square) the problems.


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