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Regulator rectifier check

SeattleRod

CB750 Enthusiast
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Hi guys and girls,

I was left stranded the other day when I was out riding my 1980 cb750c.
The battery went dead and I had to jump it 3 times to make it home.
I knew the rotor was on its way out measuring only 3.5ohms, so I went ahead and got me a new one. This one reads 4.5ohms.
Brushes have plenty of life left, so I checked the charging system with the bike running. At idle, the battery volts read 12.8 and at 3000+rpm the volts are 12.9.
Checkin the voltage reg/rectifier per the manual, the ohms read 430,400,430 on the yellow leads against the green lead and the same reads in reverse. I also get the same read between the yellows and the red/white lead.
Per the manual, the proper readings are either high (2000 ohms) or low (5-40 ohms).
Is my r/r busted already? I bought this one not that long ago, although it's Chinese.

Thanks.


 
What scale are you using to measure that? Reason I ask is that those diodes commonly take a small 'hit' of power to trigger the one way action, they will read the same both ways if too small a voltage is used to check them. Look at your meter and see if it has a dedicated 'diode check' function, they often do, and read using that. That function provides the hit needed to switch the diode to blocking power one way.

If the new rotor is used then immediately suspect it as being bad too, most used ones sold on ebay are commonly bad. A rotor can check good and still be bad, the wraps only shorting when it's spinning, the centrifugal force does it, then goes back to testing good while sitting still. I've even had them work fine at lower rpm, you go higher and then it shorts, slow back down and good again.
 
Thanks amc. The rotor is new but it's from Caltric and I've had issues with them in the past. The scales I was using were "200" and "2k" since the correct readings per the manual were "5-40" and "2000". I don't see any diode check function on my meter. It's a cheap one from harbor freights. But then again, I have to admit, when it comes to electrical issues, I'm borderline mentally challenged. Here is my meter.

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Just to the left of the 200 ohm, move the dial one more click counterclockwise there. The arrow going right to strike a + sign thing. That's the diode check position.
 
You know what, after reading your response, I did go back to the bike and checked the rectifier on that setting, the diode check and I had 0 reading and no sound.


 
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