Optimistic rev counter

My rev counter works ok, except it reads almost double the actual engine speed - i.e. it reads about 7000 rpm when in fact we're cruising happily at 3-4000.  It resets to zero ok when turned off.  Other clocks are working fine; even the MFA works!

Any suggestions anyone?  Had a search of past posts but didn't turn up anything…

There is a resistor on the board at the back of the clocks , it may have failed .
Not an easy one to sort sorry .

chudd said

There is a resistor on the board at the back of the clocks , it may have failed .
Not an easy one to sort sorry .

Hmm, sounds ominous… thanks for the tip.  I think this one stays somewhere well down the 'to do' list