Rev counter won't work

[dbell]

Hi all, I took my 325 sport out of winter hibernation this morning and noticed the Rev counter wouldnt work, I had the battery disconnected during the winter, not sure if this had anything to do with it, as it was working fine when I parked the car up!
Or Is it possible the little batteries behind the dash have given up?

Thanks in advance.
David.

[dbell]

Have just checked the wiki, and going by it the batteries are exhausted, is this a big job?

[Brianmoooore]

Replied to this last night, but it looks like I forgot to press 'submit' again!
Yes, duff SI board batteries are a strong possibility, but note that disconnecting the battery didn't cause the problem, it just exposed it.
Get the cluster out and at least check the batteries, even if the tacho. comes back to life in the meantime, because duff batteries tend to leak corrosive liquid which will destroy the SI board.
Batteries are easy enough to change if you know how to use a soldering iron, but be aware that your board may be fitted with one of two different types which cannot be interchanged.
If you search my posts (or possibly the wiki?) you will find the part numbers of suitable batteries from CPC Farnell.

[dbell]

Drove the car this evening to a local park, and on the way I noticed the Rev counter has come back to life, and continued to work perfectly on the journey there and back. I will take on board that this will probably be temporary and the batteries will inevitably need replaced.

Thank you for the detailed reply Brian.

David.