1975 85hp Johnson charging questions?

[boxchevyman]

1975 85hp Johnson.
Model: 85ESL75E
The battery is only displaying the battery voltage of 12.6v when running or not. The motor runs great. I have a service manual, so i decided to look at the rectifier first. I did a quick test.
I took the negative MM lead to ground, then went to wire 1,2,3. these are the readings.
wire 1, continuity
wire 2, no continuity
wire 3, continuity
I then reversed the leads and took the positive MM lead to ground, these are my readings,
wire 1, continuity but some resistance
wire 2, no continuity
wire 3, continuity but some resistance
With that information should i assume the rectifier is shot and this is the cause of my system not producing a charge?
Just for more information i also attached a picture of the the underneath of the flywheel the stator looks ok-ish to me but whatever you guys think?

thanks!
James

 

[racerone]

Rectifier is not expensive.

 

[F_R]

I'm sure you probably are correct, but you guys get me all confused when you describe your tests. Allow me to tell you how to do it another way.

There are 4 diodes in that rectifier. Each one allows current to flow in one direction only. So, lets test them one at a time.

First off, does your multimeter have an analog dial? If it does, great. If it is digital, does it have a diode test function? If it does, use it. If it doesn't, it might not even work...but try it anyway.

1. Connect your MM leads to ground and either yellow wire. You should get either a high or low reading on your meter. Now reverse the leads. If you got a high reading before, now you should now get a low reading. If it passes those two tests, you just tested diode #1 and it is good. If it flunked, you can stop now, because the rectifier is shot.

2. Do the same exact thing between the other yellow lead and ground, then reverse the leads. That's diode #2

3. Do the exact same thing, but between red lead and either yellow lead, then reverse leads. That's diode #3

4. Do the exact same thing between other yellow lead and red lead, then reverse leads. That's diode #4.

Note, that's four tests, times two as you reversed the leads. Eight tests. It must pass all eight to be good. Flunk any one and it is junk.

Now, wasn't that simple?

BTW, you can also use a battery powered continuity light for the tests. Lights up one way, no light when reversed.

 

[boxchevyman]

Hey F_R,

I have an analog and a digital I tried both. The only test I DIDN'T do was red to yellow. I always had a MM lead to ground. That being said I got no resistance (as in a continuity light you be lit) in both directions for both the yellows and ground with negative to ground and then with the lead reversed.

So acording to info you have it sounds like i don't need to go back and test the red wire. i will go ahead an order a rectifier.

thanks for your time.
James

 

[Vic.S]

1975 85hp Johnson.
Model: 85ESL75E
The battery is only displaying the battery voltage of 12.6v when running or not. The motor runs great. I have a service manual, so i decided to look at the rectifier first. I did a quick test.
I took the negative MM lead to ground, then went to wire 1,2,3. these are the readings.
wire 1, continuity
wire 2, no continuity
wire 3, continuity
I then reversed the leads and took the positive MM lead to ground, these are my readings,
wire 1, continuity but some resistance
wire 2, no continuity
wire 3, continuity but some resistance
With that information should i assume the rectifier is shot and this is the cause of my system not producing a charge?
Just for more information i also attached a picture of the the underneath of the flywheel the stator looks ok-ish to me but whatever you guys think?

thanks!
James

Not a complete test but enough to show the rectifier is shot.


1 and 3 are yellow AC input from stator. 2 is red ? positive output

For full test

test between:

ground and 1 (yellow), and between ground and 3 (yellow) . Reverse MM leads and repeat. Should get infinite resistance one way , very low resistance the other way

Now test as above between

2 and 1 and between 2 and 3. Reverse MM and repeat As above should get high resistance one way and low resistance the other

Final ( optional) check: Test between ground and 2 and reverse. Should get high resistance one way low the other..

Does not always work with digital meters on all resistance ranges..

Should use the Diode test range if fitted ... testing diodes is what its for.


Never disconnect your battery whie the engine is running or you could fry the rectifier.

Never ever connect the battery the wrong way round. Rectifier will be toast in an instant if you do

 

[Fed]

What's the point of the optional test Vic?
In fact if one diode was open circuited the optional test would still show up as the bridge being OK.

 

[F_R]

Hey F_R,

I have an analog and a digital I tried both. The only test I DIDN'T do was red to yellow. I always had a MM lead to ground. That being said I got no resistance (as in a continuity light you be lit) in both directions for both the yellows and ground with negative to ground and then with the lead reversed.

So acording to info you have it sounds like i don't need to go back and test the red wire. i will go ahead an order a rectifier.

thanks for your time.
James

Ok, as I said, you guys confuse me. The only way I could understand what the heck you said was to draw the circuit out on paper and give numbers to the wires, and look at the current flow. So, if I am reading and understand you correctly, you have two bad diodes in that rectifier, the two attached to the red wire.. Go ahead and buy a rectifier. Unless you want to double check using my method.

 

[Vic.S]

What's the point of the optional test Vic?
In fact if one diode was open circuited the optional test would still show up as the bridge being OK.

Not a lot of point.

Perhaps more useful to do first.. If it fails no point in going through the rest.

I only included it because IIRC Joe Reeves has included it in his tests on the Engine FAQ's board

 

[Vic.S]

Hey F_R,

I have an analog and a digital I tried both. The only test I DIDN'T do was red to yellow. I always had a MM lead to ground. That being said I got no resistance (as in a continuity light you be lit) in both directions for both the yellows and ground with negative to ground and then with the lead reversed.

So acording to info you have it sounds like i don't need to go back and test the red wire. i will go ahead an order a rectifier.

thanks for your time.
James

By not testing between the red and the yellows you could have missed a single failed diode but since you got no continuity either way between ground and red it means that both the positive end diodes are open circuit.

The "continuity but some resistance" readings between ground and the yellows is wrong too. If you had continuity one way you should have no continuity the other

Its completely shot. 2 diodes open circuited and the other two partly short circuited by the look of it!

 

[Vic.S]

Ok, as I said, you guys confuse me.

Sorry I described testing the way I did because thats the way the OP described what he did ... I had to draw it and label the wires too! If I was actually doing it I might do it your way, or I might do it the way the OP did.
Not fussed really. same load of tests, just done in a different order.

 

[hondam]

Do you know anyone that works on cars? A full system test with a midtronics battery tester works on outboards too, I use my exp-1000 all the time. It will tell you if your stator has no output or any bad diodes in your rectifier.

If that's not available here is how you test it according to CDI

 

[F_R]

No Title

OK, lets put this thing to rest. Vic.S, my comment was not directed to you. You know what you are talking about. The OP is the one that had me confused.

Now, I'm attaching a sketch of a Bridge Rectifier to show what we are dealing with here.

1. If a continuity test were to be made between wire 2 (red) and ground, current can flow through all four diodes in one direction. And blocked by all four in the other direction.

2. But what if diode D2 were open? Current could flow through the other series pair, D3 and D4 in one direction. In the other direction, it would be blocked by D1 and D2 on one side, and D4 and the open D3 on the other side. It would PASS the test, continuity in one direction only, even though it has an open diode.

3. Ok you ask what if D2 were shorted? In one direction, current could flow through 3 good diodes, plus the shorted one. In the other direction, current would be blocked by the two good diodes in one series pair, and by the remaining good diode in the other series pair. It would PASS the test with a shorted diode also.

There are other scenarios, but suffice to say this by itself is not a valid test.

The "some resistance" in the forward direction is to be expected because all diodes have "some" resistance. That "some" would be doubled when testing two in series.

BTW, the OMC factory service manual says to test it exactly the way I described earlier.