| QUOTE |
| The frequency/voltage converter circuit relies on an RC network, changing either the R or the C will change calibration. I have converted a couple of 6 cylinder ones to 4 cylinder in the very distant past, and it wasn't hard. If initial inspection of the circuit does not obviously show which are the timing components, you can simply connect the tachometer to the engine, and whilst running use a lowish value, non-electrolytic capacitor (say around 0.1uF) and touch it accross any likely looking capacitors. When you see the needle move you've likely found it. The reading will be 50% too high with a 6 cylinder engine, so you'd need to increase the value of this cap by 50%, or increase the value of the ascociated resistor by 50% (will probably be connected to this cap at one end). The gauges I modified had a trim pot for calibration IIRC, so I upped the value of the resistor and then fine tuned the calibration with this pot, using a signal generator and frequency counter. |
