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Author Topic: So what's the consensus on rectifiers for CB750's?  (Read 10808 times)

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Offline Tugboat

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So what's the consensus on rectifiers for CB750's?
« on: October 14, 2011, 11:13:25 AM »
I think mine is going out. Last weekend at Barber my battery was out of juice by Sunday. I chalked it up to the low-speed riding I'd been doing around the festival all weekend and figured that once I got on the interstate it would charge back up. Long story short, it did, and I made it back to Nashville.

Then, last night, I took it out to meet some friends and once I got to the bar we were meeting at, my turn signals wouldn't work and my headlight was super dim. Luckily there was enough juice in the battery to be able to kickstart it when we were ready to go, but the starter wouldn't even turn. Again, it made it across town and even the starter worked next time I fired it up.

So, do these things go bad "all at once" or can they intermitently fail? And if I have to replace it, what's the consensus on the replacement part?
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Offline CycleRanger

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #1 on: October 14, 2011, 11:19:52 AM »
The usual, search the forums, double check/clean all the connections, get a multimeter - test the rectifier, test the regulator, check the battery.  What you find dictates course of action.  :)

Also, what wattage headlight do you have?  Stock or aftermarket ignition components?

After market reg/rec replacements are various and cheap.
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Offline MCRider

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #2 on: October 14, 2011, 11:38:29 AM »
I am really lame on electricla stuff, so take it for what it is.  I think rectifiers can fail in thirds. There is a way to test, i think for continuity.
 Check the forum or a manual.
Also, if you look at the paint on each plate. If it appears bubbly, that plate has overheated and failed.
That's all I almost know. Good luck.

If it were mine I'd call/email that guy making solidstate components, he can tell you straightaway how to test.

http://www.oregonmotorcycleparts.com/rectifiers.html
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Offline Duanob

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #3 on: October 14, 2011, 11:38:38 AM »
After diagnosis if you still need one this guy makes a decent one.

http://www.oregonmotorcycleparts.com/SOHCfours.html

You have to dial it down a bit which I still have to do. My system is putting out 15.5v at times but mellows out as the battery charges up.
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Offline KRONUS0100

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #4 on: October 14, 2011, 03:24:03 PM »
running a rectifier and and a regulator in mine from Oregon Motorcycle Parts.  Good quality stuff, and I have had no issues since installing way back this spring.
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Offline MCRider

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #5 on: October 14, 2011, 04:51:35 PM »
Quote from: rotortiller on October 14, 2011, 03:23:11 PM
Quote
Again, it made it across town and even the starter worked next time I fired it up.

Obviously the charging system is working so you either have a drain, bad connection, left the ignition on, or have a weak battery. Next time it happens check the voltage directly at the battery.
believe me i know I'm fartin out my ass here, but if one plate of the rectifier is bad, I think you only get 2/3 of the charging effect. that would cause the symptoms he describes. Seems like its charging, but just not enough.  So rectumfier is #1, regulator a distant #2.
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Offline CycleRanger

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #6 on: October 14, 2011, 05:26:26 PM »
Quote from: MCRider on October 14, 2011, 04:51:35 PM
Obviously the charging system is working so you either have a drain, bad connection, left the ignition on, or have a weak battery. Next time it happens check the voltage directly at the battery.
believe me i know I'm fartin out my ass here, but if one plate of the rectifier is bad, I think you only get 2/3 of the charging effect. that would cause the symptoms he describes. Seems like its charging, but just not enough.  So rectumfier is #1, regulator a distant #2.


You may be, but that's TMI.   ;)

Yes, the rectifier has six diodes. As I understand it if a couple of the diodes go bad it won't produce enough voltage.
It's easy to test the rectifier with a digital meter either using the ohm setting or using the diode setting.
Search the forum for testing rectifier.  Also search for cheap regulator rectifier.

I just replaced the rectifier on my bike with a solid-state rectifier because I was having charging issues and I couldn't get a good reading from the old rectifier.
I tested the new rectifier and got good readings so I was confident I was doing it correctly and the old rectifier was bad.
That and my charging problems are gone!  :)
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Offline bluezboy

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #7 on: October 14, 2011, 05:30:55 PM »
Quote from: KRONUS0100 on October 14, 2011, 03:24:03 PM
running a rectifier and and a regulator in mine from Oregon Motorcycle Parts.  Good quality stuff, and I have had no issues since installing way back this spring.

 Ditto on the rectifier and regulator from Oregon Motorcycle Parts, I have them on my bike too and I haven't had any charging issues at least.  Now about my other problem...........
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #8 on: October 14, 2011, 10:27:26 PM »
Tug,

The rectifier has 3 circuits to cut AC voltage to DC voltage by eliminating one of the ALTERNATING electrical pulses made by the ALTERNATOR in each of the 3 yellow wires. If it isn't ALTERNATING it then becomes DIRECT with current flow only going in one DIRECT current and not ALTERNATING. That being said and as it was said the rectifier could either be doing a 100% job, a 66.6% job, a 33.3% job or a 0% job. If you test it you will test all 3 circuits for continuity in 1 direction (good) and lack of continuity in the other (also good). Any deviation and it's jacked. Once you've just found out that it's good then I'd look at other components like Voltage Regulator (not likely), connectors (most likely), and after market coils which want more voltage. Don't jump on the after market reg/rect bandwagon until you determine it's necessary to replace one &/or the other. It doesn't hurt to switch but it may not help either. I consider a solid state R/R an upgrade. I've used Electrosport's unit myself.
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Offline Tugboat

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #9 on: October 16, 2011, 10:25:16 AM »
Yeah, I'm leaning towards a bad connection somewhere... either at the plug or somewhere else along the way. It seems that when it works, it does charge the battery all the way back up. New battery, too. Guess I'll start there and see what's up. Thanks for the advice fellas - will report back. In the meantime, going for a ride this afternoon but I'm bringing my jumper pack!! :)
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Offline CycleRanger

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #10 on: October 16, 2011, 12:10:02 PM »
http://www.oregonmotorcycleparts.com/connectors.html 
Also sells plugs & connector kits cheap.
Unfortunately they're showing out-of-stock at the moment but I'm sure they'll get more.
I must have gotten the last ones a couple of weeks ago when I replaced the plug & connectors for my alternator and built my new rectifier! :)
« Last Edit: October 16, 2011, 08:19:50 PM by CycleRanger »
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Offline Rgconner

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #11 on: October 16, 2011, 08:06:48 PM »
Quote from: MCRider on October 14, 2011, 04:51:35 PM
  So rectumfier is #1, regulator a distant #2.
Whoa whoa whoa there buddy...

back away from the tailpipe!
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Offline MCRider

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #12 on: October 16, 2011, 08:16:07 PM »
Quote from: Rgconner on October 16, 2011, 08:06:48 PM
Quote from: MCRider on October 14, 2011, 04:51:35 PM
  So rectumfier is #1, regulator a distant #2.
Whoa whoa whoa there buddy...

back away from the tailpipe!
Darn forgot to use the spell checker again...  ;)
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Offline bryanj

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #13 on: October 16, 2011, 11:29:38 PM »
But on old british bikes the Lucas circular type was under the seat in such a position it WAS a rectumfrier!!
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Offline TwoTired

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Re: So what's the consensus on rectifiers for CB750's?
« Reply #14 on: October 17, 2011, 12:05:47 AM »
Quote from: bryanj on October 16, 2011, 11:29:38 PM
But on old british bikes the Lucas circular type was under the seat in such a position it WAS a rectumfrier!!

 ;D ;D


FYI:
The six diodes can short or open when gone bad.  Neither is a good thing.   ;D
Each one is responsible for 1/6th of the charging output. Assuming they fail open, you can subtract 16.7% of max output for each diode that opens.
A shorted diode(s) will usually melt wire insulation, if the battery still has remaining power to do that.

Cheers,
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