[Mgs] mga 1500 with early 5 main mgb engine

[Paul Hunt]

Have you disconnected the tach with the engine running and confirmed it 
stops?

You can check the calibration using an old-fashioned trickle charger but 
if it's not working with coil current passing through it then it won't 
work on that either.  The only thing you can do (apart from sending it 
away to someone) is to open it up and look for any broken connections in 
wiring and an the circuit board.  If you are familiar with electronics 
there are certain tests you can do inside.  This circuit 
https://www.classictiger.com/techtips/motach.html is of the early tach 
with the external pickup and this one the later internal 
http://www.mgb-stuff.org.uk/harvit.htm.  It can also be converted to the 
later voltage pulse type with a module as here 
http://www.mgb-stuff.org.uk/rvctach.htm

PaulH.


On 08/08/2023 20:35, dave northrup wrote:
>
> I do not know the origins of the tach.  I have no idea what is inside 
> it and I have not taken it apart. The car came to me in kit form.  I 
> don’t really even know if the tach worked.  Any way to test it?
>
> I do know that with the tach hooked up the engine runs, so power is at 
> least going through it.   this is the only source of power for the 
> coil.  Anyone have an mgb electic tach to sell?  I’d like to hook up 
> something that is a known quantity.
>
>
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