Tachometer Fix

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For those of you frustrated with their tachometer that doesn't work, this may be a solution. I set about building a completely new and independent tachometer driver. This isnt a tutorial, just giving people ideas. If youre not confident in making a circuit and troubleshooting it afterwards, best skip this.

You'll need to grab yourself a CS8190 integrated circuit. They come in a 20 pin and 16 pin configuration. I would recommend the 16 pin one, as it can be mounted into an IC socket. At the time only the 20 pin was available to me and it was a pain to manually solder the very small pins. Theres plenty on ebay.

Other than that you'll need to pick up all the components listed in the PDF circuit diagrams.

After all the shopping was done, it was simply a matter of mounting the circuit board to the back of the cluster, as seen in the pictures.

Disclaimer: So far I have only used this with an aftermarket ECU, as the tacho output on my standard ECU doesn't work. However, the tacho works using a ground switching signal, and so the stock ECU should work.

Tip 1: I also have the ATTESA ecu connected to the tacho signal. If you are using this tacho on a 4WD application, putting a diode between the ATTESA and ecu reduced jitter in the tacho.

Tip 2: I subsequently made a remote mounted trimpot that I can reach under the dash without having to dismantle everything just so I can make adjustments to the tacho. The instructions list a 250k trimpot, however it is too sensitive. The target resistance is around 150k ohms. This can be achieved with a 100k resistor in series with a 100k trimpot, and will give you finer control. Perhaps even 125k resistor with a 50k trimpot.

Finally I have the accuracy in an acceptable range. While it is accurate to about 3000rpm, it gradually reads too fast. 7000rpm on the tacho equates to about 6500rpm engine speed. You can change this with the trimpot, but you will have to choose your accurate range. If it is accurate at high rpms, it will read too low at low rpms.

CS8190-D.PDF

datasheet cs8190.pdf