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| Smith tacho problem https://ausmini.com/forums/viewtopic.php?f=2&t=99766 |
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| Author: | MPP67 [ Mon Mar 16, 2020 4:11 pm ] |
| Post subject: | Smith tacho problem |
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 |
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| Author: | 9YaTaH [ Mon Mar 16, 2020 5:00 pm ] |
| Post subject: | Re: Smith tacho problem |
Might be the movement is "stuck"...can you disconnect it and gently flick it to see if the pointer moves? |
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| Author: | minijcar [ Mon Mar 16, 2020 5:45 pm ] |
| Post subject: | Re: Smith tacho problem |
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 |
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| Author: | MPP67 [ Mon Mar 16, 2020 7:44 pm ] |
| Post subject: | Re: Smith tacho problem |
The tacho is the modern variety and is 4 years old. It was working perfectly two weeks ago so I'm a little confused. |
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| Author: | 9YaTaH [ Tue Mar 17, 2020 5:58 am ] |
| Post subject: | Re: Smith tacho problem |
minijcar wrote: 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 Ouch  
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| Author: | minijcar [ Tue Mar 17, 2020 5:46 pm ] |
| Post subject: | Re: Smith tacho problem |
Check power (green) and earth (black) to the Tacho first before you panic and try to find a 20 roll pack of toilet paper. |
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| Author: | 9YaTaH [ Thu Mar 19, 2020 6:43 am ] |
| Post subject: | Re: Smith tacho problem |
minijcar wrote: 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 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... |
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| Author: | minijcar [ Thu Mar 19, 2020 5:16 pm ] |
| Post subject: | Re: Smith tacho problem |
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. 
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| Author: | 9YaTaH [ Thu Mar 19, 2020 5:43 pm ] |
| Post subject: | Re: Smith tacho problem |
minijcar wrote: 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. 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 
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| Author: | Morris 1100 [ Thu Mar 19, 2020 6:35 pm ] |
| Post subject: | Re: Smith tacho problem |
Richard wrote: Why do you have to remove the battery from the car to recharge it? What a ridiculous comment. And never jump start a car? Do you actually understand automotive electronics at all? Clearly not.  Do you know who you are lecturing? |
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| Author: | 9YaTaH [ Thu Mar 19, 2020 6:52 pm ] |
| Post subject: | Re: Smith tacho problem |
Richard wrote: Why do you have to remove the battery from the car to recharge it? What a ridiculous comment. And never jump start a car? Do you actually understand automotive electronics at all? Clearly not. https://www.youtube.com/watch?v=22tBYD-HMtA |
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| Author: | MPP67 [ Fri Mar 20, 2020 3:31 pm ] |
| Post subject: | Re: Smith tacho problem |
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. |
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