Izit my Alternator or Regulator / Rectifier ?

[vluke]

Hi all,
my charging system is not, well...charging.
I've a '91 ST, with the 40amp alternator upgrade done some 12+ yrs ago.

This past weekend,
I noticed the voltmeter not reading the usual 13.5v with all lights on,
but 12.5v, and decreasing as the ride continued.
Until it got to 10.6v, and the bike would barely stay alive.

I thought it was my 5yr old+ battery finally calling it quits.
Bike made it to Sears, and got a new bat.
Still about a 1/2 hr from my destination, I watched the new battery go from 12.5v,
down to 12.0 by time I got there. So, no charging system.
Once at my hotel, I checked all fuses, wiring, and connectors.
All good and nothing burnt.
And then leaving the next morning,
I watched it go from 12.0v, down down down....blahhhh.

Being my '91 ST has the 40amp Alt,
the regulator/rectifier is piggybacked on the alt unit.
Now the s-load of questions...
How can I check which is the culprit ? The alternator itself or the reg/rect unit ?
What are the ohm resistance readings ?
And how do I test either ?
Can I get to it by simply removing the rear wheel and not the whole swing arm assembly ?
And...can you just replace one or the other ?

I appreciate any assistance.
thanx all.
Vincent

 

[The Cheese]

As I have never done the swap, I can't be of much help to ya. But I do know if you want to remove the alt, swingarm must come out. But, to test it, you just have to access the write loom for it. No need to get to it. If you have a digital volt meter, just start the bike and put it on the batt. It should read around 14.5 volts. If not, its not charging. Something about check for continuity between ground and the alt windings. An check for amps while bike is running. Our something choose to that. Is late.
A Honda repair manual will be your best friend. I suggest you get one. It will save you money. I would scan mine for ya, but I'm pretty damn lazy. And my scanner will not work with my new Linux box.

 

[Avtrician]

It could be the reg/rectifier package, or it could be worn brushes and slip rings in the alternator itself.