3 replies to this topic

[eero]

I was changing the facias on my instruments and managed to break the needle off on my rev counter. Used a dab of super glue to reattach it, but the rev counter no longer works. It used to work without any issues.

 

The needle moves when pushing with my finger so it doesn't look like I glued the shaft solid. So I'd expect to see maybe some movement, even the slightest, but it just sits still.

 

Checked some of the electrics - ground and positive are there, connection from the coil seems to be good, though I don't know what voltage I should see from there. The board in the counter seems to be good - paths seem solid, no burnt or swelled components, connection to the magnet reads about 100R so seems intact.

 

 

 

I fear the real route is finding a replacement, but they seem a bit hard to come by and aren't cheap, so I'm looking for any tips or ideas to try first. And I don't have a unit I could lend to test whether the fault is indeed within the rev counter and not somewhere else.

 

 

 

It's a '92 SPi, 8000rpm tacho with single connection to the coil.

 

 

So any ideas are welcome, even the wildest stabs in the dark!

[RedRuby]

I think that the rev counter has two wires going to it, my 93 doe's anyway, one is fitted with a flat spade connector the second with a round bullet type connector check to see if both are connected as you only mention one.

That's the back of the rev counter I mean

Edited by RedRuby, 17 June 2014 - 05:36 PM.

[eero]

The flat spade is positive, +12V, and that is connected and has power, measured it.

 

The round bullet connection off the coil is connected as well. As the same lead should run to the ECU (according to Haynes schematics) and the car runs just fine, I'd say whatever signals need to travel along it are fine and reach the tacho.

 

Though I guess I should connect my ACR and verify, don't know why I haven't yet 

 

 

As I really didn't do much to the counter I'm starting to think it's not electrical and rather physical - breaking the needle and glueing it back together is all I really did. Thinking about it - a rev counter is more or less a precision device and the magnetic force used to move the needle needs to be pretty accurate. So it could very well be that the small amount of glue I put on there is enough to throw it off balance. There was a trimmer on the PCB, it has to adjust something, so my current plan is try to turn that and see what happens. Though if this is the case I'd still expect to see some juddering or something. 

 

At least that's my current convoluted working theory 

[eero]

Took the rev counter apart again and had almost complete success repairing it.

 

Thinking that breaking the needle was all that happened, my theory was that it was something mechanical/physical rather than electrical. And true enough - there was fair amount of glue in the small brass channel up top, which probably seeped down due to gravity before it was properly set. The needle did move freely, but I guess there was enough friction which the springs or the electromagnet could not overcome. As I now know the mechanism needs to snap back to 0 by itself - that should've been the heureka moment first time around.

 

So I cleaned up all the glue and redid the needle, letting it dry face side down. Took a couple of tries but I got there in the end.

 

 

And it started to work! Though not quite perfect, off about ±100~200rpm. When trying to find the error I did mess up the springs a little and needed to adjust the trimmer on the PCB to get the reading into the right ballpark. At least I no longer have a completely dead instrument and the rough reading is close enough for everyday driving.