SOHC.co.uk Forums > CB350/400
400 four earth points
exvalvesetdabbler:
Trying to expel an electrical gremlin. Up until last week I hadn't been out in the dark for over 30 years. After 20 minutes with the headlight on battery voltage had been pulled down to 12v that was cruzing on A road with about 5000 rpm. Day time riding no issues
Currently going through all the connections and testing reg and rect on the bench.
Currently trying to track down where the loom gets it ground connection from. I have found 2 so far, one underneath the tool tray and the brass strip on the rectifier. Have I missed one or is that it?
I have ruled out the bonding on the headlight/indicator bracket and the rear lights since the green wire is providing ground to parts that are rubber mounted.
Traced all the wiring associated with the alternator, rectifier and regulator.
Yellow wires from rectifier to alternator resistance within spec between each wire about 0.6 ohm
White wire from regulator to field coil 5 ohm
Red/white from rectifier back to starter solenoid battery side ok
Forward voltage drop and reverse leakage of the diodes in the rectifier
I'm going to substitute another regulator as soon as I have time. Bench testing it, the transition between mode 1 and 2 happens 13.8/13.9v. mode 3 at 15v
What I have noticed is the suspect regulator hangs when going from mode 2 back to mode 1 at about 12.3v. mode 1 to 2 at 13.4v.
Can't see why it might do that other than grubby contacts, cleaned them already.
Black wire for the regulator traces back to other black wires ok.
Accuracy for resistance / continuity corrected for meter lead resistance.
Although it didn't seem necessary I have since checked and cleaned the connectors involved just for fun.
What have I missed?
Regards
Dave
Oddjob:
Not done a 400 for a long while but most looms of that era had the main earth point near the coils. A big old round one which bolted to the frame, normally where the coils mount at the front. Bikes like the 500-4 had a specially made metal plate to aid the contact area. If that area has been painted or powder coated you’ll need to go back to bare metal to help it make contact. Same for the battery earth, bare metal next to the contact and the frame. People miss that all the time so if that’s the case you certainly ain’t on your own.
exvalvesetdabbler:
Thanks, you may be right, I do remember there being an eyelet under the horn bracket. Never clocked that it might be a main ground point.
I'll check the voltage on the green wires against battery terminal when I fire it up tomorrow. With some current flowing there should be voltage across any grubby connection. At least the green on the reg needs proper grounding to get a valid reference. I know the rectifier is grounded, no resistance between green wire in the connector and frame with it unplugged.
The frame was painted in 1983, so possible a bit of corrosion may have got in. I would have used vaseline on them at the time based on what was on the bathroom shelf. Dad used it for something, I remember him squeeling like a stuck pig one night when mother left a tub of vapour rub next to it!
Bryanj:
Regulator numbers sound about right, you need to check battery voltage when running with both lights on and off, most common problem is corroded yellow wire connectors where stator connects to loom, you can also check the ac voltage accross each of the 3 pairs of yellow wires exiting the stator
exvalvesetdabbler:
Battery voltage is 13-15 without headlight.
That's why I suspected one phase may be disconnected and the regulator was compensating up to a point. Measuring resistance between each of the yellow wires in the rectifier plug rules that out. Same for the field coil going from the regulator end of the white wire. My alternate theory was a bad earth on the reg or rect that was lifting the reference voltage of the ground locally with increased current of the headlight.
The rectifier is well bonded now, I cleaned the brass earthing strip and the contact point on the frame. It's grounded ok with the plug disconnected. It's a bit of an odd design that the regulator doesn't have bonding to the frame and relies on the harness only.
The only thing I am seeing is the regular hanging when it should be dropping back from mode 2 to 1. I have been bench testing it with an indicator bulb to simulate the field coil load.
The spare regulator that I have dug out has a tight mode 1-2 transition around 13.8 - 13.9 in both directions.
I'll have another poke around. I need to find the other earth point under the tank and check that first.
Regards
Dave
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