Easy Tachometer Fix!

I have a 1982 Rabbit Convertible where the tach wouldn't move despite confirmation that there was the right power and signal from the ignition coil. I even used a function generator to mimic the output and got nothing (50% duty cycle pulses, 10vpp at around 60hz showed reading after the fix, so try that if you want to test yours)

I asked an electrical engineer who pointed out that one specific capacitor used on the board is electrolytic, meaning it is (or was) filled with a fluid that's probably dried out years ago. I replaced it and it worked! See the attached picture for which one to change.

I would guess that this is a common problem for tachs of this age, so I'm sure someone else will run in to it. A regular 47uF cap will work, any voltage rating above 16v. Modern ones are much higher so finding one shouldn't be an issue. Hope this helps someone out, thanks!


 

cool.

Good info that!
At these voltages you can use tantalum bead capacitors in place of electrolytic ones. That's what I've done on the few I've replaced (water temp guage, oil pressure buzzer board).