I've seen lots of threads about tach replacement on our boats. The advise usually centers around jotting down the hours on the old tach and disclosing the offset to any future buyers.
For the Sea Ray tach, one would think you could just apply power on the bench for the requisite amount of time to match up the replacement tach with that of the old one. One would be wrong.
The tach requires a pulse from the engine, for the hour meter to begin "spinning". I assume this is to make the hour meters accurate with respect to actual engine run time.
What is needed is a way to fool the tach into believing it is connected to a running engine. This pulse generator does the trick. Some setup is required.
1) run positive and negative wires from the 12V power supply of your choice, to the appropriately marked terminals on both the tach, and the pulse module.
2) Run a wire from the pulse module output to the tach input on the replacement tach.
3) Place the frequency jumper on the module to the 1khz - 10khz position. (see attached image)
4) Crank both adjustment pots to their minimum values. (counter-clockwise). Note: these are 20 turn pots, so keep turning until you hear/feel a faint clicking as you turn the pot.
5) turn on the power supply and adjust the duty cycle pot such that the tack starts registering some value other than zero. AT this point you should see the hour-glass icon in the hours window, start to slowly pulse.
6) sit back and let it wind up to the appropriate number of hours.
Bear in mind that the replacement tach MUST have fewer hours on it than the target hours, as there is no way to wind them backwards. Be very careful not to overrun the target hours for this reason. If you do so, you'll need to run the engine without a tach to let it "catch up" to the overshoot. Also note, that this pulse generator is not particularly accurate. You may have to play with both the frequency and the pulse width adjustment for the tach to begin registering. Here is a picture showing the position of the controls on the module.
For the Sea Ray tach, one would think you could just apply power on the bench for the requisite amount of time to match up the replacement tach with that of the old one. One would be wrong.
The tach requires a pulse from the engine, for the hour meter to begin "spinning". I assume this is to make the hour meters accurate with respect to actual engine run time.
What is needed is a way to fool the tach into believing it is connected to a running engine. This pulse generator does the trick. Some setup is required.
1) run positive and negative wires from the 12V power supply of your choice, to the appropriately marked terminals on both the tach, and the pulse module.
2) Run a wire from the pulse module output to the tach input on the replacement tach.
3) Place the frequency jumper on the module to the 1khz - 10khz position. (see attached image)
4) Crank both adjustment pots to their minimum values. (counter-clockwise). Note: these are 20 turn pots, so keep turning until you hear/feel a faint clicking as you turn the pot.
5) turn on the power supply and adjust the duty cycle pot such that the tack starts registering some value other than zero. AT this point you should see the hour-glass icon in the hours window, start to slowly pulse.
6) sit back and let it wind up to the appropriate number of hours.
Bear in mind that the replacement tach MUST have fewer hours on it than the target hours, as there is no way to wind them backwards. Be very careful not to overrun the target hours for this reason. If you do so, you'll need to run the engine without a tach to let it "catch up" to the overshoot. Also note, that this pulse generator is not particularly accurate. You may have to play with both the frequency and the pulse width adjustment for the tach to begin registering. Here is a picture showing the position of the controls on the module.
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