Instrument cluster question

[kod81]

Hi,

I've realize I should find my answer on-line, but I'd like to be on the safe site here.

My SI board has failed. The rev counter and service indicators are dead. The rev was working in a very intermittent manner and service wasn't working at all. So I've got my mate to solder some new batteries in. My car is '89 318i but the board seemed to be replaced at some point for a newer version as the batteries were Sanyo lithium. It looked original and not like self soldering. Unfortunately the "fix" didn't help. The rev counter and service indicator are still not working - all the time now.

I've managed to source a replacement cluster removed from a '87 325i. From what I've read I will be fine using it on my 318i as long as I replace my coding plug. Is that correct?

I would replace just the board, but I am worried that the previous one broke down during batteries replacement as it is static sensitive. Is the rev counter range different on 325 to 318? Also as the car is '87 it could be pre face-lift if, if that's the case would it be an issue? I've read somewhere that the cluster are different if the have been manufactured prior or post 06/86. Please advise,

Regards,

[Brianmoooore]

The lithium battery type board doesn't suffer from battery related problems, although it does can develop its own selection of weird minor faults. Never known one of these boards produce the faults you have though.
The whole boards are interchangeable, but have very different circuitry around the battery area, so you can't fit NiCd batteries to a board designed for lithium ones, and vice versa.
Very early SI boards had a very different 'coding' arrangement, so as long as your replacement has the plug at the front right of the cluster, it is suitable.
Place the board in a freezer for 15 minutes, then measure the voltage across them. If the voltage is significantly down on what it should be, then replace them.
Electronic circuits aren't usually static sensitive when they're assembled. It's floating pins on semiconductor devices that can be sensitive. I've worked with these devices since they first became available, have never taken any significant anti static precautions, and have never damaged a device as yet!

[kod81]

Thank for your reply.
I didn't know the lithium boards don't suffer from battery problems as the symptoms I have with (rev counter and service indicator) suggested that the battery have failed.
All my other gauges are fine, including the water temp fuel and check lights.

I've measured the voltage before and after replacing the batteries and I had about 1V less on old ones - so I went forward and replaced them with new Varta lithiums, but I will follow your advise and try the freezer trick tonight.

Thanks for clearing up the cluster's compatibility for me.
Regards,