Finally got around to the Mark II design for the RVI to RVC tacho conversion, (there's always a Mark II :shock: ). First the circuit diagram:-
The design now incorporates voltage regulators, (one of which is simply used for anchorage to the tacho body), a higher current rated transistor, some extra voltage stabilisation on the IC supply and tacho input, and some transient suppression
First I cut out the board to the correct size, drilled the holes for the voltage regulators, and added the wire links and pins.
Test fitting of the board with the two regulators in place.
The board fully loaded with the components.
The rear of the board showing the track detail.
And again test fitted to check clearances. The coil winding of the tacho just misses the chip, but I already knew I would have to lay the large red capacitor on its side to miss it :shock:
I decided to use part of the original cable for the input connection...
...cut, stripped and tinned...
...and fitted to the board. I did this as it was a better fit, and gives the tacho a more original look from the outside.
Top view of completed board. Notice the large red capacitor fitted laying down as mentioned above. I also replaced the two zener diodes for ones with a higher rating.
All fitted in place and wired up.
I then added the transient suppressor to the rear of the PCB
Just about enough room in there!!!
A new cable was installed for the points side of the coil to tacho input. Soldered and ready for crimping...
...protected with a boot...
..and installed on the coil. I had already installed another new cable, (single yellow/white), for the +ve side of the coil, to make direct connection to the tacho and bypass the ballast resistor. The double yellow/white wires are now redundant, one being the original ballast wire, and the other the feed from the starter to give the full battery voltage when starting, but there is no harm in keeping them there, and I don't like aimlessly loose wires :?
The tacho end of the cable being soldered and crimped.
After a quick calibration the tacho was re-assembled and replaced in the dash...
...and back into the car
A test run of the car shows that the tacho works
, but I really need to do a side-by-side comparison with the tacho on my test meter to see how accurate it is :shock:
