Topic: 73 cb-750 charging issue?

[izaleth]

hows it going guys, i have a 1973 cb-750 and im doing the wiring, it came with nothing so its mostly all custom, i have it wired as shown below but get no increase in voltage when the bike is running what methods are available to trouble shoot both the stock charging system and the reg rec respectively to find the fault?
Using a ricks type B Reg/Rec

[69cb750]

Check inner coil has 12 volts dc
Check outer coil has 14.5 volts ac

[izaleth]

Check inner coil has 12 volts dc
Check outer coil has 14.5 volts ac

so open up the cover and while running put a power probe on the coils?

[MauiK3]

Seems like an entire harness would be easier.

[izaleth]

Seems like an entire harness would be easier.

its more or less wired as shown with nothing i can think of being able to interrupt the connection

[Bodi]

Rick's 10-100?
Should be fine, your wiring diagram looks good.
Check the wiring between the engine plug and the actual coils. Any bullets in there tend to fail from the heat cycling.
Test the coils with an Ohmmeter. The field coil should be pretty low resistance, I don't know exactly but maybe 10 Ohms?
Each output coil should have a somewhat higher resistance but the readings between any two yellow wires should be the same, three readings. All these readings can be good with bad bullets, their resistance can rise with heat from current going through them.
Neither coil can have any connection to ground from any wire, reading infinity ohms or some error code on a digital meter.
If that's all good, take a steel tool (wrench, screwdriver) and hold it to the alternator cover. With key on it should be attracted to the field coil beneath that cover. Not super strong but a definite attraction. No magnetic attraction means the field coil is not getting power or is bad. These coils are rarely bad, they can be damaged in a crash but normally they are very reliable. A wiring issue or regulator failure is most likely with no physical coil damage.
An easy system test is to connect the white field coil wire directly to a black wire (with it disconnected from the reg/rect) and starting the engine. That gives maximum output from the alternator so you should see a voltage rise if you rev it a bit. If it does that but you have no charging with the reg/rect connected then the reg is not working. (or a wiring problem as always)
If the coil resistance and tool attraction tests are all good, but still no charging, the rectifier may be dead. It takes a few milliseconds to burn that out if a battery or boost is connected reverse polarity. Measure between the yellow wires with a voltmeter set to AC volts with engine running and wires connected to the reg/rect. With a good rectifier it should be around 14-18V. A bad rectifier can cause a very low or a higher (25VAC+) voltage there, and the readings may be quite different between wire pairs.

[izaleth]

Rick's 10-100?
Should be fine, your wiring diagram looks good.
Check the wiring between the engine plug and the actual coils. Any bullets in there tend to fail from the heat cycling.
Test the coils with an Ohmmeter. The field coil should be pretty low resistance, I don't know exactly but maybe 10 Ohms?
Each output coil should have a somewhat higher resistance but the readings between any two yellow wires should be the same, three readings. All these readings can be good with bad bullets, their resistance can rise with heat from current going through them.
Neither coil can have any connection to ground from any wire, reading infinity ohms or some error code on a digital meter.
If that's all good, take a steel tool (wrench, screwdriver) and hold it to the alternator cover. With key on it should be attracted to the field coil beneath that cover. Not super strong but a definite attraction. No magnetic attraction means the field coil is not getting power or is bad. These coils are rarely bad, they can be damaged in a crash but normally they are very reliable. A wiring issue or regulator failure is most likely with no physical coil damage.
An easy system test is to connect the white field coil wire directly to a black wire (with it disconnected from the reg/rect) and starting the engine. That gives maximum output from the alternator so you should see a voltage rise if you rev it a bit. If it does that but you have no charging with the reg/rect connected then the reg is not working. (or a wiring problem as always)
If the coil resistance and tool attraction tests are all good, but still no charging, the rectifier may be dead. It takes a few milliseconds to burn that out if a battery or boost is connected reverse polarity. Measure between the yellow wires with a voltmeter set to AC volts with engine running and wires connected to the reg/rect. With a good rectifier it should be around 14-18V. A bad rectifier can cause a very low or a higher (25VAC+) voltage there, and the readings may be quite different between wire pairs.

think its the 14-100, ill look into it thanks!
ill probably start by checking my Stator to ruel it out, thanks for the info!

[scottly]

hows it going guys, i have a 1973 cb-750 and im doing the wiring, it came with nothing so its mostly all custom, i have it wired as shown below but get no increase in voltage when the bike is running what methods are available to trouble shoot both the stock charging system and the reg rec respectively to find the fault?
Using a ricks type B Reg/Rec

That wiring diagram has several errors:
The battery negative terminal should be connected to frame ground.

The field coil green wire and it's regulator green wire should also be connected to frame ground, not just each other.

The red rectifier wire should be connected directly to the battery, not through the main fuse, and the main fuse should be between the battery and the ignition switch, although this isn't related to your charging issue.

With the ignition switch on, the three screws in the alternator cover that mount the field coil should be magnetized; if not, the problem is on the regulator/field coil side of the charging system, NOT the stator/rectifier side.
 

[izaleth]

hows it going guys, i have a 1973 cb-750 and im doing the wiring, it came with nothing so its mostly all custom, i have it wired as shown below but get no increase in voltage when the bike is running what methods are available to trouble shoot both the stock charging system and the reg rec respectively to find the fault?
Using a ricks type B Reg/Rec

That wiring diagram has several errors:
The battery negative terminal should be connected to frame ground.

The field coil green wire and it's regulator green wire should also be connected to frame ground, not just each other.

The red rectifier wire should be connected directly to the battery, not through the main fuse, and the main fuse should be between the battery and the ignition switch, although this isn't related to your charging issue.

With the ignition switch on, the three screws in the alternator cover that mount the field coil should be magnetized; if not, the problem is on the regulator/field coil side of the charging system, NOT the stator/rectifier side.

but i need 2 wires going to the field coil right? which is the white and small green in this setup, what i get from this is i may have to run a leg off and ground that same wire to the bike ground as well?
the one going to the field coil?
and if working right those screws are magnetized? appreciate the info, may have glossed over that had you not mentioned it

what i take from this is i should take the green field coil wire and run it straight to the frame along with the reg/rec green?
also i have the fueses set somewhat like you have described, the battery is fused at its main connection and there are fuses here and there before major components