Volvo Penta TAMD41P-A Tachometer | Hour Meter Issue

Hey there, I have a 1998 Camano Troll with a Volvo Penta TAMD41P-A. It is equipped with tachometer/hour meter combos that have stopped working correctly. The identical tachometer's at both helms have stopped working following the replacement of the starter alternator (according to the previous owner). They still light up, but now the hours window just reads "---" and the RPM meter sits at 0, then every 20 second goes all the way to 100% and back to 0. I am assuming this is what they do out of the box when they have power but no AC pulse signal. (and we know what they say about assumptions) In any case, I do not suspect the tach's themselves since they both exhibit the same behavior directly following alternator replacement. Two mechanics have looked at it and both tell me something different, but neither have solved the issue. The first said the tach is receiving an AC pulse signal from the alternator and everything is wired correctly, so he didn't know why it wasn't working. The seconds claimed everything is wired correctly but said he was not seeing an AC pulse signal from the alternator, but he is not very familiar with Volvo electronics apparently. Before heading to a Volvo dealer and giving them a blank check, I thought I'd check to see if anyone has encountered this same issue and how they fixed it. Thanks for any insight you can provide.

I don't know your boat so this is partly guesswork.
Odds are the previous alternator had an output that sent a signal to the tachometer and the hour meter which they then converted to rpm and hours.

The new alternator likely does not have that output. OR there is a wiring problem preventing the signals from getting through to the guage.

THe backlight has its own power supply evidenced by the fact the light operates.

Check the stamped or cast letters/number on the back of the alternator and ask a good shop which should be able to tell you what they are for. Or take the alternator off and to the shop and get them to tell you what each terminal is for.
Different mfgrs. may use different stampings/castings.

The new alternator may actually not have the needed terminal.

As for actual wiring these signals are relatively weak pulses and need :
--tight connections,
--CLEAN connections , both wire side and alternator side.
--no corrosion on the wire or the terminals
--proper well done crimps where the terminals and wires join.

THe above also stands for the guage side connections.

Hope this helps sort thing out.

C lectric said:

I don't know your boat so this is partly guesswork.
Odds are the previous alternator had an output that sent a signal to the tachometer and the hour meter which they then converted to rpm and hours.

The new alternator likely does not have that output. OR there is a wiring problem preventing the signals from getting through to the guage.

THe backlight has its own power supply evidenced by the fact the light operates.

Check the stamped or cast letters/number on the back of the alternator and ask a good shop which should be able to tell you what they are for. Or take the alternator off and to the shop and get them to tell you what each terminal is for.
Different mfgrs. may use different stampings/castings.

The new alternator may actually not have the needed terminal.

As for actual wiring these signals are relatively weak pulses and need :
--tight connections,
--CLEAN connections , both wire side and alternator side.
--no corrosion on the wire or the terminals
--proper well done crimps where the terminals and wires join.

THe above also stands for the guage side connections.

Hope this helps sort thing out.

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Thanks for the very thoughtful reply. I will try those things and report back here when I discover the solution.

I have the same issues. 4 tachometers on 2 TAMD41s. The Starboard engine has the original Volvo alternator, so the tachs both work as designed.
The port engine has a much higher capacity alternator, supplied after market, and only the hour meters work, both without errors. As I understand the issues, the alternators supply a pulse that the tachometers can't understand. I have a set of digital tachometers that I haven't yet installed, as my understanding of that process is not yet complete. The port alternator has also had regulator issues, that I am also working through, so I presently rely on temperature and harmonic vibrations to get my engines synchronized properly. Since I now have Solar panels to charge the batteries, I am considering reverting back to the original Volvo alternator just to get the tachs on the port engine to work.

koliver,

After performing some additional tests this past weekend, I'm 90% sure the alternator that was installed is not compatible. I plan to install a volvo penta compatible alternator the next time I have a major server completed. If you beat me to the oem alternator install, I'd love to hear the result. Thanks for contributing.

Same problem with hour meter, not tach, on my flybridge helm station. Hour meter and tach are both fine on cabin helm station. Giving some thought to replacing FB instrument panel, as all FB meters glass is badly hazed, dark.

NCheaven said:

Same problem with hour meter, not tach, on my flybridge helm station. Hour meter and tach are both fine on cabin helm station. Giving some thought to replacing FB instrument panel, as all FB meters glass is badly hazed, dark.

Click to expand...

I still haven't replaced my alternator since everything works other than the tach's, but it's on the short list. In any case, for the haze issue, you may want to purchase a 3M headlight restoration kit from your favorite retailer. I used it on my automobiles badly hazed headlights a few months back and they still look good as new.

Thank you, "pgmtls"! I hadn't even thought of that previously. Sadly, same problem is true of my 19 year old compass on the FB - Danforth which several sources say cannot be repaired. Fluid level a low, too, but still functions apart from glass being dark.