Topic: Battery won't charge

[Brettboone225]

Hey guys new to the page. I have a 1974 cb750 836. Recently bought the bike. Battery kept going bad. Replaced battery. Started bike with electric start. Multi meter told me at idle bike has just shy of 12v. After idling for about 2-3 minutes bike would die due to lack of recharging on the battery. voltage regulator and rectifier are separate. Upgrade has not been done. Regulator doesn't appear to be for the bike...I could be wrong but per wiring diagram it looks like it has an extra spade on it. Anyway. Bike won't charge not sure how to check stator or regulator. Could use some help to get pointed in right direction. Connections seem firm. I'm thinking ac voltage is not getting converted to dc in battery or stator is not providing ac to convert. Thoughts?!

[scottly]

Welcome Brett, but this is not the proper place for questions; this should have been posted on the main bikes board. First suggestion is to check if the field coil is getting power: With the key on, a charged battery, and engine not running, the three screws on the alternator cover should be magnetized. If not, you have a problem on the regulator side of the system.
 

[70CB750]

Download shop manual here:

http://manuals.sohc4.net/cb750k/

It has detail instructions how to test the charging system.  You will need a multimeter to check voltage and resistance. 

First check the field against the ground and the same for the stator -  resistance has to be infinite.  Than check the resistance between all yellow wires for the stator and between green and white (I think) for the field coil. 

This is just from the top of my head, manual is really helpful - it has resistance values listed.