Topic: help me decipher electrical system test results - OMP Vreg update

[flybox1]

CB750K8, F3motor.
Symptom- inadequate charging.

Rpm charging test...
Battery  @ 12.87v (off charger for 5hrs)
Light /ign On - 12.06v
Idle 12.4v
2000rpm - 13.41v
3000, 4000, 5000rpm - 13.5v

Battery drain test 12.87v to start.
Light(35W H4) on - 12.06v
1min - 12.6v
3min - 12.4v
5min - 11.99v
7min - 11.89v
10min - 10.98v

Battery Pos to Vreg black - 12.87v
Battery Neg to Vreg green  - 0.00v

Rectfier diodes(ohms)
S1  -  6.97, OL, 2.46, 9.36
S2  -  5.15, OL, 3.99, OL
S3  -  5.54, OL, 3.80, OL
(The 9.36ohms on S1 makes me suspicious when the other two are OL.)
See proper diode test results below

Stator yellows measure .40ohms on all three combinations
Coil green and white leads measure 7.0ohms.
Vreg harness wires measure 7.0ohms.

Anything else I can check? 
All harness connectors I can find have been cleaned.
Vreg point has been cleaned. Vreg core and point gap checked within spec.

Thank you for your assistance.

[eigenvector]

I'd start with what you suspect - the rectifier.

[scottly]

 Rectfier diodes(ohms)
S1  -  6.97, OL, 2.46, 9.36
S2  -  5.15, OL, 3.99, OL
S3  -  5.54, OL, 3.80, OL
(The 9.36ohms on S1 makes me suspicious when the other two are OL.)

Does your meter have a diode test function? Looks kinda like this  -l<- You can't properly test a diode with a digital meter set on the ohms scale.

[flybox1]

Yes.  I have it here in front of me....

[flybox1]

With my leads in the same orientation as when I got the 9.36ohm reading...in diode testing.mode, I get OL.   Switching the leads I get .501 volts(?)

[scottly]

With the meter set to diode test mode, the meter should read about 4-5 when the diode is conducting, and OL when the meter leads for that diode are reversed . There are twelve combinations: 3 with the red meter lead connected to the rect. red, and the black meter lead connected in turn to each of the yellow wires. The next three are with the black meter wire connected to the rect. red wire, and the red meter wire connected to each yellow wire. The next 6 tests are between the rect. green wire and the yellow wires.

[flybox1]

[scottly]

While we're waiting, a diode is the electrical version of a one-way valve, or check valve. When it works properly, it only allows electrons to flow in one direction. It takes about .5 volts to turn it on, which is the reading displayed on a meter with a diode test function.

[scottly]

Your rectifier test looks good, Rob.

[flybox1]

Yeah, I think so too. 
So, what else could be preventing charging?

[scottly]

Fully charged battery, ignition switch on, can you make a bfw stick to the alternator cover?
 

[flybox1]

Nope. Not even a SFW, but I do get a little pull....

[scottly]

Disconnect the white wire from the regulator, and jump it directly to the battery + terminal and do the bfw test again. (no need to have the ignition switch on)

[flybox1]

Disconnect the white wire from the regulator, and jump it directly to the battery + terminal and do the bfw test again. (no need to have the ignition switch on)

No improvement in the magnetic field....

[scottly]

Your ohms reading from the white wire (disconnected from the reg)  to chassis ground is 7 ohms?

[flybox1]

Your ohms reading from the white wire (disconnected from the reg)  to chassis ground is 7 ohms?

7.3ohms

[scottly]

With 12+volts applied to the white wire, there should be a noticeable magnetic field??? You don't have an after-market finned alternator cover installed, do you? That might explain it. If not, did you remove the field coil from inside the cover, and install it backwards? The left side of the field coil in this pic should go towards the inside of the cover.
 

[flybox1]

When I got this engine, yes, the coil was loose from the cover.   It's possible, I guess, but doesn't it install only one way?   IIRC, there were only three mounting holes on one side.   Mine is installed as in your picture...

[scottly]

Yeah, I think it can only go one way; I'm stumped???

[flybox1]

I appreciate the immediate help.  I'll go thru the harness once more this weekend. Maybe I'll knock something loose 

[scottly]

The only other test I can think of is to connect the field coil bullet connectors under the sprocket cover directly to battery plus and minus terminals, bypassing the harness entirely.... 

[flybox1]

The only other test I can think of is to connect the field coil bullet connectors under the sprocket cover directly to battery plus and minus terminals, bypassing the harness entirely....

To rule out a bad field coil?   Is there an incorrect orientation?

[scottly]

No, to rule out a harness issue.

[Spanner 1]

I think it's a bad ground on the field coil.... as Scottly says, bypass and connect + and - from the battery to the field coil bullets under the sprocket cover.... or you may discover they are corroded/crappy when you look in there.

[flybox1]

I think it's a bad ground on the field coil.... as Scottly says, bypass and connect + and - from the battery to the field coil bullets under the sprocket cover.... or you may discover they are corroded/crappy when you look in there.

I just had those out a few hours earlier and tested to 7.0ohms resistance.   I'll make the connections tomorrow, and pull the cover to check the wires more thoroughly...
When I do bypass the harness, what should I be looking for?  BFW-holding magnetic field?