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Topic-icon 1974 R90/6 circuit board

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4 months 3 weeks ago #3333 by Yogibrmstk
1974 R90/6 circuit board was created by Yogibrmstk
Does anyone know how to check the neutral indicator diode on the back of the Circuit board on an R90/6?

I am getting a reading of 4.6 K ohms in one direction. I am thinking this is too high and this diode is no good. Any one know specks are for this diode?

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4 months 3 weeks ago #3334 by 12990
Replied by 12990 on topic 1974 R90/6 circuit board
I wish I had the short answer...But I found the long answer to testing my diode board here:
bmwmotorcycletech.info/technical-articles-list.htm
Good luck!
The following user(s) said Thank You: Yogibrmstk

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4 months 3 weeks ago #3335 by 1872
Replied by 1872 on topic 1974 R90/6 circuit board
Diodes should read low in one direction and high in the other. Without getting out the book and finding the wiring diagram I don't know what else is in the circuit. If it is dead short both directions it is bad. The 4.6K may be OK.

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4 months 3 weeks ago #3337 by Yogibrmstk
Replied by Yogibrmstk on topic 1974 R90/6 circuit board
Thanks! very much appreciated!

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4 months 3 weeks ago #3338 by 1872
Replied by 1872 on topic 1974 R90/6 circuit board
Why is the diode suspect? I think it prevents the neutral light from lighting when the clutch is pulled, but the last neutral problem I worked on was a F bike so I may be wrong.

Bob

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4 months 3 weeks ago #3342 by Yogibrmstk
Replied by Yogibrmstk on topic 1974 R90/6 circuit board
Hi Bob,

If I knew more, I would have more to contribute but I am just learning as I go.

I lifted this from another forum from a guy named Roger Albert in Texas. I hope this cut and paste is ok to do. But Roger deserves the credit for this writing and not me.

"the diode is in a way part of the starter circuit. It allows the ground signal from the neutral switch (on the trans) to get to the starter switch which then grounds the coil in the starter relay.
Note, the switch is not 'switching' 12V, but rather applying, indirectly, ground to the relay (which already has hot/12v on the other side) This may be backwards from the way you envision it, but the coil doesn't care. The diode also blocks the 12V from the neutral light from ending up on the starter switch.
Normally, if the diode fails, the bike will think it's in gear, and not start." (Roger Albert, 11/7/04, Pelican Parts Forum)

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