Lotus Elan

Rev counter

PostPost by: Hongokongo » Sun Jul 14, 2013 4:42 pm

My Rev counter used to work correctly Now when I turn on the ignition, the needle swings all the way round, slowly coming back to zero. The needle the just gently swings around 2000 to 3000 no matter how fast the engine is going.
I have a master electric switch, and I think the problem started when the ignition was in the 'on' position when I turned the power on.

Any ideas please?
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PostPost by: billwill » Sun Jul 14, 2013 11:44 pm

Just a bit of bad luck I think.
Something in the internal electronics seems to have failed.

I doubt if the master switch v ignition key is significant, things tend to fail at the moment of switch on in any case.
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PostPost by: reb53 » Mon Jul 15, 2013 6:12 am

When mine started to play up, even though I hadn't made any changes to the cars wiring, I chased my tail for a while re-doing earths etc.

Finally came to the, ( obvious now that I think about it), conclusion that a component of some sort had failed as everything else was unchanged.
Somewhere here in the archives there's mention of a capacitor that dies, and that indeed was the case with mine.
Actually found one in an old VCR I was about to bin, but they apparently aren't unusual and easy enough to source from the usual electronics type places.

Ralph.
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PostPost by: Quart Meg Miles » Mon Jul 15, 2013 9:21 am

reb53 wrote:....Somewhere here in the archives there's mention of a capacitor that dies, and that indeed was the case with mine.
Actually found one in an old VCR I was about to bin, but they apparently aren't unusual and easy enough to source from the usual electronics type places.

Ralph.

Can anyone quote a value for this component, please. Or, indeed, can anyone supply an original or copy of the circuit for the RVI tachometer.
Meg

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PostPost by: rcraven » Mon Jul 15, 2013 9:29 am

Here's one relevant post about the capacitor: http://www.lotuselan.net/forums/lotus-electrical-f38/early-rvi-rev-counter-t19840.html
A search would probably reveal yet more information.
Robert
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PostPost by: Quart Meg Miles » Mon Jul 15, 2013 10:36 am

rcraven wrote:Here's one relevant post about the capacitor: http://www.lotuselan.net/forums/lotus-electrical-f38/early-rvi-rev-counter-t19840.html
A search would probably reveal yet more information.

Thanks, Robert,

All the published circuits use two or three transistors whereas the one in my car and another I passed on for a +2 are both single transistor models. However, it seems clear the value is 0.25uF though I have never seen one labelled thus; 0.22uF is more likely except that electrolytic capacitors, which seems to be the type, aren't reckoned to be within 50% of stated value and 25uF used to be a common value rather than 22uF.

(For the uninitiated, electronic components are specified using exponential values which give a fairly constant ratio between adjacent values. The basic E12 series is 10,12,15,18, 22, 27, 33, 39, 47, 56, 68, 82, [100]. Back in the early1960s cheap resistors were ?20% tolerance but nowadays more likely to be ?1%.)
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PostPost by: ftsoft » Mon Jul 15, 2013 11:20 am

My rev counter bounce a lot. Does anyone know if that is the same issue.

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PostPost by: reb53 » Mon Jul 15, 2013 9:01 pm

ftsoft wrote:My rev counter bounce a lot. Does anyone know if that is the same issue.

Frank


Frank,

That is exactly what mine was doing. I did all the other things discussed here to no avail.
Putting in a new cap fixed it immediately.

Ralph.
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