In a 940 turbo wagon I'm chasing failed instrument lights. Occurred episodically in the past 6 months but are completely dead now. Temp gauge also went from episodic to non-functioning, and speedo has randomly ceased over the past year or so but still springs to life most of the time.

Removed cluster and current checks out at rheostat slider wire in the cluster plug. I think I may be dealing with a ground problem. What the best sequence for troubleshooting all the possible ground points?

Any thoughts or experience with similar problems? TD

 

Most likely your problem is with the circuit board behind the instrument panel. The soldering points crack and lose contact. You need to refloat the points with a soldering iron, carefully. It may solve all your problems.

 

Thanks Lev. I've heard this before and it sounds like a way that I could easily make the problem worse. Is there any info out there on how to do this "refloating" process? I have a high quality digital soldering which I can set for specific tip temperatures. TD

The circuit board looks very clean & dry with no visible corrosion.

 

Many times the cracks in solder joints are small and difficult to see with the naked eye and can occur on a normally good looking circuit boar. I have a lamp with a magnifying lens I use for inspecting for solder cracks. Even at that, I wish I had one of those low power microscopes they use at solder stations when repairing fine pitch electronics.

The most common place for solder cracks to form is where large heavier components are mounted. The vibration over he years causes the solder to fatigue and crack

 

Thanks for those tips. I'll try to locate one of those rectangular reader/magnifiers to start my search.

If I locate any cracks I assume that I would just touch the spot with the solder pencil tip but not add any solder? Any suggestions on what temp ranch would be safe to set the tip for?

 

I refloat ALL of them. Just touch each joint with the hot tip until it liquefies.

 

I've been told that a drop of "Liquid Rosin Flux" should be put on the joint first but I'm having no luck finding that in liquid form?

Someone else said there is a danger of the hot tip sucking up the solder off the board?

Another suggestion was a little piece of copper wire between the tip & the solder joint?

Maybe I should find an old circuit board & practice?

 

You should be able to get the liquid rosin flux at Radio Shack. I would expect a local hardware store such as Ace would have it as well.

I think you are over-thinking this. Just touch each solder point with the tip of your soldering iron till it melts and re-flows. This should only take a second or two for small solder joints. Larger joints may take a little longer. If the solder doesn't melt in a second or two, use the rosin flux.

 

I do tend to over-think things which involve electricity/electronics, but there is good news worth reporting that others should not overlook before refluxing/refloating the instrument cluster PCB.

I carefully cleaned all the connectors & plugs related to the cluster, then loosened & re tightened all the screws on the back of the PCB and when I re-installed it, everything worked! A testimony to corrosion being the culprit & no doubt refluxing may be in my future but not before I have some time to practice. TD