AC generator wire olms ramp up going from lower connector to VRR

[Cocoablini]

Hi, on the hunt for the lack of voltage returning to battery. Previously I got no resistance when testing white wire to white wire as instructed by Yamaha rd400 manual in the connector by the fuse box(to reg and rect units though I have a new VRR combo).
Looking at connector pins they were awfully corroded. I sanded and cleaned them(actually every one I could see) and I started getting the near perfect resistance as cited by Yamaha of .45 olm from white to white wire. It was closer to .5 and it bounced a bit from .4 to .7.
That's a good sign that I have some continuity from stator to first connector.
The connector from generator wires to VRR however are pulling 5 olms. Is that normal or you think those wires are toast? I have no specs for 2 connector leg of the trip to VRR.

[Gr8uncleal]

On my own RD400, the lack of charging was due to a broken wire in the rotor itself.

You need to test resistance between the two copper rings on the rotor. The manual gives specs and details on how to check with the rotor removed. To test it on the bike, I attached each of the crocodile clips on my tester wires to a long nail - I used tape to insulate the shafts of the nails. Remove the two carbon brushes from the generator, put a nail through each of the holes until they touch the rotor and see what resistance you get. If zero, then your rotor needs looking at.

[tore]

5ohms are too much in a wire. Copper wires do age so it is not a bad idea to replace the cable harnesses when 30+ years.

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[Cocoablini]

That's a great hack for a test on the rotor! Do I need a puller for the rotor removal or just jam a piece of wood in the metal to keep it from spinning?

[tore]

You can also measure between the two regulator wires. If you get acceptable values you are good. Otherwise you need to remove the brushes and measure direct on the rotor.

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[Gr8uncleal]

That's a great hack for a test on the rotor! Do I need a puller for the rotor removal or just jam a piece of wood in the metal to keep it from spinning?

Neither, you just do it with the motor stationary and ignition turned off - the battery in the tester provides the power needed for the resistance test. My insulating of the shafts of the nails was basically belt and braces in case I momentarily turned the ignition on with them in situ! 

[c50]

That's a great hack for a test on the rotor! Do I need a puller for the rotor removal or just jam a piece of wood in the metal to keep it from spinning?

Neither, you just do it with the motor stationary and ignition turned off - the battery in the tester provides the power needed for the resistance test. My insulating of the shafts of the nails was basically belt and braces in case I momentarily turned the ignition on with them in situ! 

It’s only 12 volts max and fed through resistors. Just put your probes on the pins in the plug to measure  the rotor, brushes and connections properly. Or to measure the rotor just probe the slip rings, really simple.

[Cocoablini]

Rotor test was fine. What I did do though was:
-Replaced Voltage rect and reg with a combo VRR(Regulator was toasted)
-Clean the brush tips of residue
-Cleaned the copper of the Rotor(really black)
-Cleaned the Stator windings with light duty soap/water(not ruin the coating)
-Checked battery terminal connectors and cleaned them
-Cleaned the harness connectors terminals (male of female) with 1500 grit sandpaper on both lower and VRR connections

Checked the continuity again and had .45 to .5 olm with the white to white wires from AC Gen(in spec) on all connectors
Buttoned up bike and started it.
Bike started one kick
Neutral/Oil lights would pulse a bit when I rolled throttle(good sign)
Measured 13-14v on battery(great) at idle
Measured 15+ on revving over 2000k
Yay!

[Gr8uncleal]

Well done and thanks for posting what you did and the outcome. 

[Cocoablini]

Just happy the Stator and windings are not toasted! Modern VRR has better and bigger cooling fins as well. A little funny to get it to sit on the panel but works like a top

[Gr8uncleal]

Just happy the Stator and windings are not toasted! Modern VRR has better and bigger cooling fins as well. A little funny to get it to sit on the panel but works like a top

Might be my memory playing tricks on me  , but I recall that, some years back, a member here was manufacturing and selling "conversion" plates to mount the combined aftermarket regulator/rectifiers.