High all,
So I work as a mechanical engineer for a manufacturing company here in the UK and have treated myself to a new contact/non-contact tachometer. When it arrived I was pleasantly surprised as it was a nice looking unit, easy to use and worked well. However, when I checked it's accuracy I found it to be reading twice the speed that it should be. The seller is going to send me a new one by the way. But I decided "TAKE IT APART" and have a play with it. After some fiddling around I found that by changing the crystal oscillator to one of a different value I was able to get it to display almost the correct speed, but not quite. There is no calibration settings by the way. I was wondering if I could just bodge a small potentiometer in there somewhere to allow me to fine tune it as there is no calibration setting. The original crystal was 4Mhz. By replacing it with a 6 Mhz crystal it increased its accuracy. If bodging a small potentiometer in there somewhere is even possible, I would not know where to put it as my electrical knowledge is somewhat limited. Just thought it might be cool to modify it instead of just throwing it away. I have included some detailed images of the PCB if anyone has any ideas.
Sorry, just noticed after posting that I have labeled two ic's the wrong way round.