Charging System Problems 70hp Johnson

[cchase]

I'll try not to get too long winded, but want to give all the info I have on my problem...<br /><br />About a year ago, my tach started acting goofy. Then on a trip two weeks ago, the charging system started putting out 17-18 volts. Did a little searching around on this site and came up with replacing the rectifier should resolve the problem.<br /><br />I replaced the rectifier and did not get any sort of change in what I was seeing on the gauges. At a high idle, my voltmeter still shows ~17 volts and my tach doesn't work (goes to 4,800/5,000 and hangs there). Wondering if I got a bad rectifier, I put a multimeter on the battery terminals when it was running and I was showing 12v +/-.<br /><br />My questions is, with what I am seeing consistent with getting a bad rectifier or may there be other gremlins that I will have to chase? Any help is much appreciated as electrical is not one of my strong suits...<br /><br />Thanks in advance,<br />Craig

 

[rickdb1boat]

Re: Charging System Problems 70hp Johnson

Hello and Welcome CChase <br /> Test the recitifier per this post by Joe Reeves. This should give you a clue as to what is going on... BTW-Joe is the resident OMC guru..<br /><br /><br />(Small Rectifier Test)<br />(J. Reeves)<br /><br />Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction. <br /><br />Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other. <br /><br />Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires. <br /><br />Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

 

[cchase]

Re: Charging System Problems 70hp Johnson

Thanks, I'll give that a shot.

 

[cchase]

Re: Charging System Problems 70hp Johnson

I ran the test on the rectifier and all had resistance one way and no reading with the leads reversed and when grounded through the red wire, the resistance measured lower than grounded through the case so it appears that the rectifier checks out.<br /><br />Is it a possibility that the high voltage (highest I saw on the gauge was 18V) when I was running may have damaged my gauges? Are there any simple diagnostics I can run to check to see if the signal the gauges (tach and voltmeter) are getting are accurate or at least there or am I stuck with replacing the gauges and seeing if that cures the problem?<br /><br />Thanks,<br />Craig

 

[angus63]

Re: Charging System Problems 70hp Johnson

First things first. Flywheel magnets are all there and secure? Stator charge coils not oozing and resistance checks out? Wires from coils to rectifier continuous? Input voltage good to rectifier? Output voltage good from rectifier? Wires from rectifier continuous to batteries? All grounds are clean and tight? All battery connections (including batt switch) all clean and tight? Pretty much after that I'm stumped.<br />Good luck