Aston Martin Tacho repair.

[Murphyv310]

Hi.
A friend of mine asked me to repair his Aston Martin DB6 Rev counter. The car has been converted from positive earth to negative but the Smiths Tacho has been bodged.
This what I intend to do: https://youtu.be/WAuFgzDS5zE
I've done the same at least twice before with the 4 cylinder smiths gauges and it works 100%.

[Radio Fixer]

Sounds a good way to go and a very nice video. You are a natural !

Gary

[Murphyv310]

Part 2 is here. https://youtu.be/LHjlNvzZX6I
All now working but not as yet calibrated, that comes tomorrow!!

[Murphyv310]

Hi.
The third stage is to check the calibration and set it up. Prior to that it is wise to replace the .22uf cap with a modern high stability type. The recommended way is to use a signal generator on the secondary of the coupling transformer with a square wave. I decided to use a tone generator app on my phone. This has worked a treat and the calibration is spot on at 3000rpm and about 5% error at the ends of the scale, still within Smith's 7% error and well within their staggering 10% error.
I'll be doing a final YouTube video later on.
May I say this movement is the same as in Humbers, Singers, Rovers and Volvos of the 60's so fully relevant.

On a 6 pot engine the frequencies are as follows.
3000rpm....150Hz
6000rpm.....300Hz
1000rpm......50Hz
Etcetera

[Murphyv310]

Hi.
I did have some problems with one of the AC187's so I have substituted two AC127's
There is a diagram here but watch out for the deliberate mistake: http://www.sw-em.com/Smith%27s%20Tachometer.htm

[Murphyv310]

Here is the final video https://youtu.be/TBS119WwHg0
It is now retuned to its case, cleaned up and been fully wrapped in bubble wrap. I'll be posting it off in a very sound box and it will be extremely well padded.
Nice "different" job to do and a satisfying result.

[Radio Fixer]

Nice job and a good result.

I haven't got one of those smart phones (couldn't drive one lol ) so it would have to be a sig gen and counter.

Gary