repairing a Smith

KLAS · Post by **KLAS** » Sun Aug 26, 2007 5:04 pm

after MJLJ runs perfect and my smith tacho is working with the great help offered here i bring in a not MJLJ related problem:
my smith tacho is sometimes jumping around (it started doing this long before MJLJ). maybe someone could say "replace part x and y".
and i found that it is reading a bit low, it shows 3800RPM, but the MJLJ software shows 4000RPM. all other RPM are close enough i don't see any differences. maybe its because the 4000 is staight up and the mechanic/electronic has a hart time pushing the hand up.

fikus01 · Post by **fikus01** » Tue Aug 28, 2007 5:36 pm

on the back of a smiths tacho on the curcuit board there is a variable resistor that allows adjustment or what the needle reads!! mite be worth a twiddle!

KLAS · Post by **KLAS** » Tue Aug 28, 2007 5:53 pm

not on this one. the full electronic are some condesators and an ic.
i know such a potentiometer is fittet to the newer Nippon-Seki instruments.
but this tacho is only showing a bit less at 4000RPM. all other RPM are spot on.
the biggest problem is the swinging of the needle. sometimes the needle is spot on and won't move randomly, suddenly it starts to swing from 2000 up to 5000 RPM and back and so on. after some seconds its back resting at the correct number.

any idea?

fikus01 · Post by **fikus01** » Wed Aug 29, 2007 6:18 pm

well when a points a distributor are fitted, id be expecting to see a failing condensor or coil or some badly adjusted points! im not sure how that equates to mjlj tho!! could be interferance on the saw/pip!! depends where u take your rpm reading from i guess! im no mj genious im afraid, tho i do know my points and dizzyz! im just looking to upgrade my brain!

KLAS · Post by **KLAS** » Wed Aug 29, 2007 6:41 pm

a good point to mention, the tacho did not care about the way it was triggered, it swinged with points, than with the electronic of the factory ignition system of my SPi mini and still does now triggered by PIP.
thats why i think its a fault inside the tacho, one of the 6 electronic parts failed. but i don't have a clue how it works.

DannyP · Post by **DannyP** » Wed Aug 29, 2007 10:45 pm

You might have a marginal coil wire in the movement, or one of the connections to it. If it gets hinky then settles down and works ok I would look for a bad connection internally, since it has been there no matter what the rpm source.