Technical Rev Counter Not Working

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Technical Rev Counter Not Working

Pull9Gs

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I have loosened the instrument panel to see behind it and none of the wires are obviously hanging off. Where is the sender? I am assuming it is electronic?
The needle doesnt move at all, any ideas?

This is on a '77 1300 that is being put back on the road after over 10 years being garaged.

Thanks.
 
There is no sender as such - the feed to the instrument is directly from the coil in the engine bay. It just "counts" sparks from the coil to the distributor.

Odds are the wire at the coil end is disconnected or damaged...
 
Thanks jimbro1000

Ive had a look at the coil and 5 wires (including HT) are firmly attached. I am now assuming it is a broken wire or some other connection or maybe a problem with the dial itself.

Does anybody know which wire it is exactly?

Thanks
 
All the wiring is in place and I have tested it up to the molex connector on the back of the instrument panel and it is all fine.

Therefore it must be the dial itself. Does anybody know what the third connection labeled "1" is, the others being + and -, and any ideas how to test/fix the dial. The needle moves when the panel is tipped.

Thanks
 
"1" is the connection to the coil negative terminal, which is also called "1."

+ and - are ignition supply and earth respectively.

In the X1/9, the rev counter uses a simple integrator circuit, that tots up the ignition pulses; the faster the pulses come, the higher the output voltage from the circuit. The gauge itself is just a moving coil meter, just like your other gauges.

If you know a bit about electronics, you can test the integrator circuit and the connections to/from it, I believe the circuit uses discrete components that can be replaced if you are handy with a soldering iron.
 
If you know a bit about electronics, you can test the integrator circuit and the connections to/from it

I can use a multimeter and know basic electronics so can you give me advice on what to test exactly?

Thanks rachaeljf
 
I just had a look inside a spare cluster. I have a Bertone anticlockwise tachometer. The tacho driver circuit has an 8 pin DIL IC, with the number 8610 on it. This kind of suggests something like an LM8610 IC, but I cannot find a record of such an IC. Anyway, it looks like a simple op amp based integrator circuit, with a few cheap resistors and capacitors.

To get to this circuit board, you will need to dismantle the tachometer, which carries a good risk of ruining it anyway!

If you can identify the input and output of the driver circuit, you can check its operation by applying a signal from your coil (either use a signal generator or connect it to your engine). With + and - connected, you should be able to read an output voltage with your test meter, which should increase smoothly with increasing engine revs.

Similarly you can check the moving coil meter by applying +, - and a variable voltage to see if it responds.

It may help to look at some application circuits for ICs like LM2917, you could make up your own tacho driver circuit based on them.

I don't really have the expertise to tinker with this sort of stuff, I would be inclined to source a s/h replacement tacho or take it to someone like Speedy Cables!
 
One simple thing I missed - the instrument clusters are notorious for bad connections caused by corrosion getting under the little brass nuts on the backs of the gauges. Try removing them and giving everything a clean with a small wire brush or wire wool (but don't let bits of wool get into the gauges!). Also check for electrical continuity between the relevant pins in the Molex connectors on the back of the cluster and the actual brass studs on the backs of the gauges. Might save you a lot of hassle!
 
Thanks rachaeljf

I have been through and wire brushed/wet and dried the nuts, washers and terminals, including the molex connectors. Unfortunately that hasn't worked either.

Tomorrow I am going to put my external rev counter on the connectors on the back of the gauge to try and prove that there is a connection between the molex and the back of the gauge. If there is then I don't know what to try after that, new gauge I suppose... :(:confused:

...tacho driver circuit has an 8 pin DIL IC, with the number 8610 on it. This kind of suggests something like an LM8610 IC, but I cannot find a record of such an IC.
This is past my knowledge of electronics;) I will look into it if necessary.
 
It isn't unheard of for the circuit boards to degrade or crack. It hasn't been so much of an issue here in the UK but in the USA a lot of cars have suffered this fate (possibly because more cars have survived the rust problems).

A simple continuity test can identify any damaged tracks on the circuit board, no real need for another rev counter except as a final test.

The IC could be at fault - 30 year old ICs aren't particularly well know for their longevity with the ceramic casings simply turning to dust when disturbed. Thankfully the simple chips seem to survive better and the chip in this case is pretty rugged - but not infallible.
 
It is definitely the gauge itself that has broken.

I have taken out the 2 screws on the back of it and nothing seems to come apart???
What should I be checking exactly to find out which bit is broken?

Is it possible to replace the gauge or do I have to get a whole new instrument panel?

Thanks
 
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