Troubleshooting a VDO tachometer.

[Movutomu]

I am having problems with a VDO viewline tachometer - can anybody advise??
The boat is a vintage Freeman with a basic petrol engine circa 1965 - the original tacho being a dodgy old Smiths. This I replaced with a new VDO viewline tacho which receives pulses from the negative side of the coil just above the points. Immediately the engine is switched on and ticking over the needle on the VDO swings straight to show max full revs - 4000 rpm - but a handheld tacho reader confirms the expected 600 rpm. I have checked and rechecked the dip switch settings and wiring to be correct according to the supplied installation sheet.- and any contact with VDO simply redirects me back to this. I have also tried another VDO tacho with the same result so the instrument would seem to be ok - the problem must be in the installation. Can anybody help ??

 

[rogerthebodger]

Do you have the model number of the VDO tacho as there are numerous types,

 

[Movutomu]

Rogershaw - the part number is A2C59512431.

 

[rogerthebodger]

Rogershaw - the part number is A2C59512431.

This site talks about specialised software to calibrate so you may need to talk to your supplier.

http://www.howardinstruments.com.au...id=7919&mdid=433186cf844551718f8eaf28ffbd8950


Is this the instructions you have

http://www.vdo.com/media/182669/flc_tachometer_without_display_viewline_85_en.pdf

This talks about optional software and also shows switches also.

 

[Movutomu]

Yes Roger, that is the information sheet I have. Sadly it has any number of technical errors, as did its previous reprint, so it maybe isn't too helpful. The number of pulses to be read are set out on the table on page 4 - and you only need the software if you want to set the instrument to a pulse number not shown.

 

[rogerthebodger]

There's a interesting comment about adding a diode into the points circuit.

" For standard, points ignition system, add a IN4004 diode in series with the signal wire (cathode towards tacho)"

If you didn't do this it may be the problem of it could have blown the tacho, lets hope not.

http://www.ebay.com/itm/VDO-Viewlin...00-RPM-85mm-3-Black-A2C59512431-/141775365402

 

[Movutomu]

Yes, I've tried the diode - and another site which suggests a resistor - but neither seems to work.

 

[Billjratt]

If it goes straight to FSD (full scale deflection) when power is applied (IGN on, before starting the engine) it could be wired wrongly - or at least that has happened to my instruments during a (professional) refit.
Without a picture of the instrument, it's a bit of a guess, but the hint is that the "G" terminal (if there is one) is NOT ground - it is the german for 'sender'... They can be especially confusing if the unit is designed for isolated earth operation where the real ground terminal is very obviously insulated and looks like an input.