SI board faults - Possible dry solder?

[votivequagmire]

Well first off I knew I needed to replace the batteries in the SI board as there's a good chance they are the original ones. The Inspection/Service lights did not light at all and I also had a problem with the tacho occasinally.
So I sourced the batteries and had them delivered last week. I removed the old batteries and fitted the new ones no problem. I was very pleasantly surprised to discover that the replacement batteries had the solder lugs in exactly the right places so no modification necesary to fit.
After refitting the clocks to test, I'm still not getting any Inspection / Service lights and now the tacho doesn't work at all?
I've cleaned the contacts to the tacho and I noticed that the tacho needle, if moved, doesn't return to the 0 position again? Is this an indication of a fault?
Additionally, after closely inspecting the SI board itself I noticed that the solder and component sides are coated with a reddish film which I can only guess is some sort of protective glaze. I can see that a considerable amount of the solder joints to the individual components appear to be quite dry and some have a distinguishable ring which usually implies that there is a potential connectivity issue? Has anyone else had any experience with these in that respect?
I have electrical and electronic experience so if there is a known procedure which fixes these types of faults how would I go about obtain such?
Or is it simply a case of reflowing all suspect solder joints and then suck it and see?
All advice appreciated.

[Brianmoooore]

Are your batteries the lithium type? Have you fitted the right type? There are known issues with the tacho. needle moving off the stop when the engine is switched off with the lithium boards, but it doesn't affect operation when the engine is running.
The SI board doesn't normally suffer from dry joints in my experience, since there's no components on it that you normally associate with dry joints, such as components that mechanically stress a joint or run at high temperatures. I've seen the 'rings' that you describe, but I don't think they're actual cracks, but there's always the possibility of an exception to the rule. Takes a bit of heat from a soldering iron to get through the board lacquer, but a bit of reflowing with a small amount of flux cored solder won't hurt anything.

[votivequagmire]

Thank you Brian. Yeah I sourced the lithium batteries from CPC, I have an account with them. They're Varta rather than Sanyo but they're the correct ones. Is there a way of getting hold of a picture of the printed circuit board to trace the tracks through for testing continuity? Predominantly around the battery area but would be better if I had the whole board.

[votivequagmire]

I guess that's a no then

[Brianmoooore]

Sorry, I missed your reply. I don't normally get email notifications of replies except on rare occasions, and if I open and subsequently close the E30 zone, without checking all the highlighted
posts, then I'm unlikely to see it.
No, I don't know of any circuit diagrams or PCB diagrams for the SI boards, other than the very small sections I've needed to trace over the years.
I've never found a dry joint on the SI board - cluster dry joints are confined to the pins for the speedo. sub board, the infamous 220 ohm resistor, and occasionally on the rear socket pins, although the latter is usually physical damage caused by the incompetent removing the plugs.
The tracks are very thin in places, and if juice from a corroded battery gets under the lacquer, it usually causes havoc.

[votivequagmire]

No problem. Thanks for the reply Brian. I can see this is going to be another long repair process. Do you happen to know where the lithium type battery connectors connect to on the board? I'm having no service / inspection lights and I think I have a faulty tacho. Would it help if I attach the service light reset tool or would it be pointless until I have any life from the SI board? Sorry for the multiple questions. I've never had this problem from any of my previous E30's. I even successfully connected a twin AA battery holder to one which enabled me to replace batteries without removing the cluster. Just had to drop the cover under the steering column. I'm wondering if I should just get a replacement SI board to save some extra grey hair. But I don't think that will solve the tacho issue.

[Brianmoooore]

A replacement board is the route I'd take. There's no point in wasting time and effort on readily available cheap parts.
The electronics for the tacho. are on the SI board - the instrument itself is just a meter movement, so, as long as the tacho. signal is reaching the cluster, I'd expect it to work.
I think I remember one case where a non working tacho. was down to a faulty coding plug.
If you get a replacement board, it's always a good idea to change the batteries before fitting if they are the NiCd type, and at least test them if, or replace if the board has been left disconnected from a car for a long time without being switched off on the jumper or the wire link, if they are the Lithium type.

[votivequagmire]

Understood, and thanks.