Dazzer Posted December 31, 2018 Report Share Posted December 31, 2018 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 Quote Link to post Share on other sites
DaveN Posted December 31, 2018 Report Share Posted December 31, 2018 Could it be an intermittent short in the feed to the switch? Quote Link to post Share on other sites
Dazzer Posted January 1, 2019 Author Report Share Posted January 1, 2019 Hi Dave Does sound logical and ive checked previously but what i might do is swap all the trigger wiring out. Cheers D Quote Link to post Share on other sites
RogerH Posted January 1, 2019 Report Share Posted January 1, 2019 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 Quote Link to post Share on other sites
Dazzer Posted January 7, 2019 Author Report Share Posted January 7, 2019 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 Quote Link to post Share on other sites
Griff52 Posted June 18, 2019 Report Share Posted June 18, 2019 Hi Darren I ooking through the forum I found this thread I have a logic box with the sane fault did you ever find the problem ? Alan Quote Link to post Share on other sites
Icarus60 Posted June 18, 2019 Report Share Posted June 18, 2019 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 Quote Link to post Share on other sites
ntc Posted June 18, 2019 Report Share Posted June 18, 2019 You need to check the earth lead is good and nothing else connected to it or it will find any earth it can. Quote Link to post Share on other sites
Griff52 Posted June 20, 2019 Report Share Posted June 20, 2019 Thank's for all the info I'll check all the wiring and switches, may be start again. Thanks Alan Quote Link to post Share on other sites
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