Tacho trouble 1990 Johnson 90hp

[markoc85]

Hi there, does anyone have any advice on troubleshooting my tachometer?

It worked fine, then intermittently for a day, and now it doesn't work at all damnit!

Any starts much appreciated!

 

[markoc85]

Re: Tacho trouble 1990 Johnson 90hp

Ok just had a good look around in this forum, tested motor and it appears not to be charging.

So I assume the rectifier needs replacement would that be correct?

 

[psteurer]

Re: Tacho trouble 1990 Johnson 90hp

A bad rectifier would cause this problem. Make sure that your engine is not charging before going to the expense of a new rectifier. A simple test is to use a volt ohm meter set on DC volts. Put the leads on the battery terminals and test your voltage. Then run the engine and test the voltage while running. You should be seeing between 13-14 volts when the engine is running. If you do not get that, then check the leads for corrosion. If you do get that voltage, then check the leads on the back of the tach for corrosion. Also, rotate the selector dial on the back of the tach. Put the indicator back to the position you found it in.

 

[ezeke]

Re: Tacho trouble 1990 Johnson 90hp

There are two threads in the Engine FAQ dealing with the problem, depends on the type of rectifier, regulated or unregulated. The tach gets its signal from one side of the the rectifier/charging system, so it is possible to have a failing rectifier and still have some charging.

See: http://forums.iboats.com/showthread.php?t=190638 and/or http://forums.iboats.com/showthread.php?t=190636

 

[robert graham]

Re: Tacho trouble 1990 Johnson 90hp

Check for loose/corroded wiring/connections on back of tachometer, also remove/check/clean fuse to tachometer. Move small switches on back of tach back and forth. If your tachometer is a 1990 model then you may need to replace it. Mine lasted about 8 years before the moisture finally killed it. My new tachometer is "waterproof", but sometimes I see a bit of fogging on the inside of glass dial, so how "waterproof" can it be? Good Luck!

 

[markoc85]

Re: Tacho trouble 1990 Johnson 90hp

Ok I tested battery voltage and its not charging so I guess I need a new rectifier. This is the thing mounted under the flywheel at the back right?

Does anyone know the spec of this rectifier such that I might be able to save some coin by jury rigging a cheap rectifier from an electronics store which has the same spec?!

 

[markoc85]

Re: Tacho trouble 1990 Johnson 90hp

Ok I tested battery voltage and its not charging so I guess I need a new rectifier. This is the thing with about 5 wires mounted under the flywheel at the back, correct?

One last thing does anyone know the spec of this rectifier such that I might be able to save some coin by jury rigging a cheap rectifier from an electronics store which has the same spec?!

 

[bktheking]

Re: Tacho trouble 1990 Johnson 90hp

Ok I tested battery voltage and its not charging so I guess I need a new rectifier. This is the thing with about 5 wires mounted under the flywheel at the back, correct?

One last thing does anyone know the spec of this rectifier such that I might be able to save some coin by jury rigging a cheap rectifier from an electronics store which has the same spec?!

No that doesn't mean the rectifier is bad, that just means "it's not charging". You need to test the unit with a meter by itself and verify it is bad in order to avoid throwing away money. That unit is a combo rectifier/regulator and if it is bad needs to be replaced with the correct part # 0523589. The old systems with the separate rectifier can be replaced with a sqare rectifier but not this one unfortunately.

Read:

http://www.cdielectronics.com/downl...ues, Regulator-Rectifiers and Tachometers.pdf


The diode check for the rectifier is the simplest test to do with a meter (even easier if it's got the diode function). If you've got a bad diode you will know right away if the meter reads something in both directions, should read infinity only in one direction.

 

[McGR]

Re: Tacho trouble 1990 Johnson 90hp

Note on using meters to test rectifier diodes:

Most of the modern digital multimeters are high impedance and can't turn on a diode junction. Using the Ohm setting on newer meters will usually provide misleading results that usually read in over 1M Ohm in both directions. This is why they provide a diode test function on the new meters.

Most older analog meters applied enough voltage to turn on the diode junctions. I most cases the older Ohmeters did a good job of testing rectifiers. On the newer meters the Ohmeter function won't test the diode properly. Therefore, you have to use the diode test function.

 

[markoc85]

Re: Tacho trouble 1990 Johnson 90hp

Ok thanks I've got a decent RMS multimeter with a diode function.

How do I do a diode test to check if rectifier is dead? Rectifier/regulator has 5 wires - which ones do I test?

 

[ezeke]

Re: Tacho trouble 1990 Johnson 90hp

There is no simple foolproof DIY test for a watercooled regulated rectifier like there is for an unregulated rectifier. If it is not charging, you are better off to replace it. OE 0585195 or http://www.iboats.com/mall/partfind...d_poid=334784&gd_row=197&**********=313343003

The CDI installation instructions also telll how to test (troubleshoot).

http://www.cdielectronics.com/InstallSheet/193-4204.pdf