Tach not working past 2000 RPM's (help)

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bmurray

Petty Officer 2nd Class
Joined
May 16, 2002
Messages
152
My tach on my boat with an 85 Johnson 150hp, stopped working while at the lake this weekend. It works good up to about 2000-2500 rpms and then drops to 0 when you get past it. Any insight would be great. thanks, Bob :confused:
 
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petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: Tach not working past 2000 RPM's (help)

what is the voltage at the battery when this happens? Check your rectifier/reg and related connections...
 
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bmurray

Petty Officer 2nd Class
Joined
May 16, 2002
Messages
152
Re: Tach not working past 2000 RPM's (help)

one more clue, when sitting docked and using the fast idle set at about 2000, if I lightly touch the trim buttons, the tach will bounce. Thanks for the reply schematic, I will try to check the retifier. Any details on this test that you could shed on me? Thanks
 
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petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: Tach not working past 2000 RPM's (help)

I would check all grounds.....<br /><br />The rectifier is nothing more than four diodes. To check them, you will require a digital multimeter with a diode test function, or an analog (needle type) meter with an ohmmeter function set to RX1.<br /><br />
diode2.gif
 
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suzukidave

Petty Officer 1st Class
Joined
Jul 1, 2000
Messages
387
Re: Tach not working past 2000 RPM's (help)

Bumurray<br /><br />There is a teleflex technical note for certain johnrudes from that era with very similar symptoms to yours. It requires a resister to fix. Check page 4 of this link<br /><br /> http://www.tflx.com/PDF/99320.pdf
 
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bmurray

Petty Officer 2nd Class
Joined
May 16, 2002
Messages
152
Re: Tach not working past 2000 RPM's (help)

great info, I will look into this. The only thing that bothers me is that it was working until I took off with the motor in the tilt and it slammed down to the trim rods. This is when it started doing this. Thanks for the info. :)
 
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