Faulty speedometer

[Gabriel70]

Hi

My home is in Melbourne, Australia.
Today, I decided to try and fix my speedometer.
This problem started approximately ten years age when my speedometer became erratic and died within minutes.
I have examined  the instrument cluster numerous times.
Today, I decided to remove the long, thin circuit board located under the speedometer on the bottom right of the instrument cluster.
I examined the board and noticed a very faint burn mark underneath the electrolytic capacitor, located near the green capacitor.
I flipped the board over and noticed a burn mark focused around the electrolytic capacitor.
I removed the capacitor and took a few photos of the board.
I’m now looking to purchase a replacement board.

Regards

Gabriel

[rbm]

Hi,

Have you tried to clean the burn off the board and replace the electrolytic capacitor with a new one?  You might also want to replace the green capacitor as well.  It looks to be a tantalum one and they tend to self-destruct over time.  It might work and save you the cost of a new board.

[Gabriel70]

Hi

I replaced the 10μf electrolytic capacitor and the speedo is now working.
I’m not certain how to minimise the condensation inside the gauge cluster.
It’s a 1984 k100.

Thanks

[Laitch]

I’m not certain how to minimise the condensation inside the gauge cluster.

The BMW/Motometer solution to this problem was to make holes in the rear of the instrument case then cover the holes with GoreTex fabric—at red arrows in the attached photo of a later model instrument cluster. That seems to have done the trick. Be certain the case gasket is in the correct position when the case is screwed together. Using a thin coating of flexible silicone sealant on the gasket will help stop moisture penetration.