Roveragedkid
New Member
The tacho was dead when I bought the car. I removed it from the binnacle and gained access to the innards by drilling the 4 brass rivets. Great care must be taken not to touch the face or damage the needle. I first drilled with a 2mm bit to 10mm depth for screws to refit, then with a 4mm bit to remove the rivet heads. The unit was held by the 4 metal fixing brackets in turn for this and care was taken that no swarf entered the tacho. 3 screws were then removed from the backplate. The rubber grommets and seal may give some difficulty in separating the casing from the mechanism due to adhesion. The diagram below is for the tach. fitted to a Lotus Europa, but is very similar to the 1972 Rover P6 tach. The C1 capacitor which was 2.5uF rather than the value shown in the diagram and was electrolytic and polarised was found to be short-circuit. This was replaced with a 1uF non-polar capacitor which should not go short-circuit as the original did. It is much larger physically but did fit. I then reassembled the tacho. using self-tapping screws in place of the rivets. A friend did the electronic testing and replacement of the capacitor,and tested the circuit again afterwards. I shall refit the instrument to the car in the morning. It may need calibrating. There is a screw for adjustment under the brown sticker on the back with the legend 'do not remove'. My friend was not surprised that the original capacitor had failed due to what he regarded as an unsuitable specification. It is located behind the silver transistor (3 legs) and is longish and cylindrical with a + sign at one end. This and the transistor are the two most likely components to fail I believe. This is an RVI tachometer which is unlikely to work with electronic ignition, which is not fitted to my car. When removed from the car the two bullet connectors may be joined together if it is desired to start the car. Take care that the loose spade connector does not short out on anything by covering it temporarily with tape. I shall report progress after reinstalling the unit.
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