Hello brains trust,

my Smith tacho was working fine. Jumped in the car on the weekend to enjoy a drive and noticed that the tacho resting position was 1,000 rpm even when the engine was off, and did not register any revs when the engine was running. I have checked connections to the coil, earth and power but it has me stumped. Any ideas? Or better still, anyone located on the Brisbane southside who could come and have a look?

Mark

Might be the movement is "stuck"...can you disconnect it and gently flick it to see if the pointer moves?

_________________
"Show me the Mini!"

If it is an original Smith Tacho from the 60’s or 70’s then yes I agree with 9y.
If it is a modern Smiths Tacho with a stepping motor movement then it will be an absence of ignition power or earth to the Tacho. The stepping motor must be powered to move. It has no hairspring to return it to zero like earlier examples. Beyond that, a transient voltage spike from a jump start or the like will take out the ic or micro

_________________
1960 Morris Mini Minor

The tacho is the modern variety and is 4 years old. It was working perfectly two weeks ago so I'm a little confused.

Ouch

_________________
"Show me the Mini!"

Check power (green) and earth (black) to the Tacho first before you panic and try to find a 20 roll pack of toilet paper.

_________________
1960 Morris Mini Minor

I have worked on military systems using steppers and they were quite reliable...sounds like the modern Smiths Tacho might benefit from some spike protection in front of it...

_________________
"Show me the Mini!"

Stepping motors in Automotive and Commercial applications have had their ups and downs with respect to reliability particularly where vibration and dirt are present. The cost and extended lifetime of non military items have an impact. Very few military vehicles drive 300000 automotive km’s Or 1000000 plus commercial km’s
They have been used since the mid 1990’s and are more stable in general
Spike protection is a nice idea and in most cases it is implemented in some fashion but inevitably if it is severe in amplitude and short on duration it is very difficult to stop.
The solution is to stop it from happening. For example I would never jump start a car. Much as it is inconvenient you need to remove the battery and recharge and reinstall. Please feel free to disagree, the practice has provided me with a steady source of income over the years.

_________________
1960 Morris Mini Minor

1990's...Hmmmm a little later than that my experience by at least 20 years...Yep agree with off car recharge after having an older NRMA gorilla pop an alternator regulator with his ham-fistedness

_________________
"Show me the Mini!"

Do you know who you are lecturing?

_________________
"Show me the Mini!"

Problem solved. Looks like there was an issue with the internal workings of the tacho (slightly annoying given it is only 4 years old). Re-installed in the mini and working just like a bought one.

thanks for everyone's suggestions and advice.