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Logic overdrive fault.


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Im wondering if anyone has experienced tracing an intermitent fault on logic overdrive? (Revingtons variety) I have theories but nothing conclusive. Fitted on my rally mk1 saloon. 

Works perfectly on 2nd 3rd and top the momentary switch flips it in and out or changing gear does the same, Its been fitted 12 months. However, in this time occassionaly it engages itself... occassionaly is maybe once or twice every couple of days. Doesnt seem to be related to anything and only engages, never drops out unexpectedly.

Up to now Ive swapped the momentary switch, swapped the relay, changed the box and overdrive unit! Not because of the fault but upgraded... checked the wiring and all appears to be correct.

Theory, maybe the momentary switch type im using is incorrect or a bad batch? Could an inhibitor switch on top of the box trigger it if it earthed against the body or is faulty? 

Struggling to find a fault. Anyone else experienced this?

Many thanks for any suggestions.

Cheers

Darren

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Hi Darren,

         I have a similar box but not Revington.

Does your Momentary Switch ground the input or supply a 12V pulse.  Mine supplies a 12V pulse but is not important.

The inhib switches are normally Open Circuit so if they fail then nothing happens.

However they normally fail by going Open Circuit. Should the internasl fall apart then perhaps they could short out inside and ground the logic relay.

Disconnect the wiring so that only the 4th inhib switch is in circuit and see what happens.  If nothing after a few days then change to the other switch.

 

Roger

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On 1/1/2019 at 6:18 PM, RogerH said:

Hi Darren,

         I have a similar box but not Revington.

Does your Momentary Switch ground the input or supply a 12V pulse.  Mine supplies a 12V pulse but is not important.

The inhib switches are normally Open Circuit so if they fail then nothing happens.

However they normally fail by going Open Circuit. Should the internasl fall apart then perhaps they could short out inside and ground the logic relay.

Disconnect the wiring so that only the 4th inhib switch is in circuit and see what happens.  If nothing after a few days then change to the other switch.

 

Roger

Thanks Roger

Will do 

Darren

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  • 5 months later...

Hi Alan , DarreN 

I have a Revington unit and looking my scribbles it looks like the only way it could select  overdrive is if there is a positive pulse given to the internal little latching relay and the unit is grounded through the inhib switches. If the inhib switches break then that OD will drop out and will not re-engage until the selector switch is pulsed on again ( provided that the inhib switches are remade )

So it must (?) be the switch pulsing high without being selected to do so. It could be the equivalent of a bouncing switch rather than one having a crisp bang bang action. This assumes that the Revington unit hasn't failed/shorted internally.

Best of luck

Rog

 

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