MK1 LED strip tacho fix

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B-Hive
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MK1 LED strip tacho fix

Post by B-Hive »

My lervly new MK1's bar graph tacho does not work.

And aside from exploring the obvious (like wires to coil etc) does anyone have any info on what usually causes this blackout to occur,?
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Tim Leech
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Re: MK1 LED strip tacho fix

Post by Tim Leech »

If the whole thing doesnt work, it may be a broken wire or bad connection? Theres not enought Mk1's around for it to be a common fault like it is a on a Mk2 diesel (my Mk1 Diesel works ok).
Lots of Motors, mostly semi broken....
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mat_fenwick
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Re: MK1 LED strip tacho fix

Post by mat_fenwick »

How easy is it for you to take the rev counter out? Failed components may be visible evident, otherwise someone who knows electronics should be able to test at least some components

If you have a 12V battery charger you can test the rev counter out of the car. There should be 3 connections to the unit; 12V supply, earth and trigger from the coil. Connect the supply to the +ve connection on a battery, and the earth to the -ve. Connect the -ve lead of the charger to the -ve battery terminal also. Connect the +ve lead from the charger to the trigger connection, but not to the battery. There will likely be enough of a ripple in the DC output of the charger to display a reading on the rev counter.

Disclaimer - I've not tried this on a LED bar graph type rev counter, but it worked on an analogue (petrol) type. (I was converting a 4 cylinder rev counter to accept an input from an 8 cylinder engine, so needed to halve the number of input pulses, but don't own a frequency generator!)

EDIT - Just to explain a little more - on a 50 Hz mains supply you should see a reading of 3000 rpm. The ripple in the charger output will be twice the mains frequency (this caught me out to start with as I thought the rev counter was reading too high) because the troughs in the AC signal are rectified to become peaks in the output.
100 Hz = 100 cycles/second
100 * 60 = 6000 cycles/minute (equivalent to 6000 sparks a minute)
6000/4 = 1500 cycles/minute (sparks/minute for one cylinder)
4 stroke engine therefore sparks every 2 revolutions
1500 * 2 = 3000 rpm
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