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Old Rotax 912A ignition

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3 months 1 week ago #21821 by Bumble2
Old Rotax 912A ignition was created by Bumble2
Hi All, I am trying to trace an ignition fault on my 912A engine. The ign coils and modules are in an aluminium box rather than mounted on the engine as in later engines. Does anyone have a cct dial for this old system to help fault find?

There are 4 pairs of wires coming from the mags, each pair white/red and white /green leading to the modules. Two pairs have a red sleeve, I'm not sure which are the trigger pair for elimination purposes.

Background:
Large 400 tpm drop on one Mag, even at cruise speed, changed plugs, changed caps, swopped red wires, fault stays with same mag. Can't check trigger gap unless I remove engine so trying to eliminate module / coils. HELP !!!

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3 months 1 week ago #21824 by RobSeaton
Replied by RobSeaton on topic Old Rotax 912A ignition
It is most likely a ground issue. the alum box mixed with steel hardware can be a problem.
drill a 1/2" hole in the box and run a good sized ground wire (at least 6AWG) from the coil brackets to a good airframe/ engine ground. Use a grommet to seal the hole.
Replace any corroded bolts and clean the contacting surfaces. apply Dow DC4 or dielectric grease to the connections

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3 months 1 week ago #21827 by Bumble2
Replied by Bumble2 on topic Old Rotax 912A ignition
Thanks Rob, as you can gather, I've been chasing this for some time so I'll give that a go tomorrow and keep my fingers crossed. Have you any idea where I can get a cct diag for this old system ?

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3 months 1 week ago #21830 by RobSeaton
Replied by RobSeaton on topic Old Rotax 912A ignition
What is a cct diag?

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3 months 1 week ago #21834 by Bumble2
Replied by Bumble2 on topic Old Rotax 912A ignition
Sorry Rob, cct diag is my shorthand for Circuit Diagram - the later engines have a 6 pole plug to the modules, earlier ones have 4 pole plugs. Mine has 4 x 2 pole plugs so I'm trying to understand the circuit before I swop them around for fault finding. Hope it makes sense.

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3 months 3 days ago - 3 months 3 days ago #21884 by RobSeaton
Replied by RobSeaton on topic Old Rotax 912A ignition
see heavy maint manual 74-00-00 3.21.2
and attached

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Last edit: 3 months 3 days ago by RobSeaton.

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3 months 1 day ago #21913 by Bumble2
Replied by Bumble2 on topic Old Rotax 912A ignition
Thanks Rob, thats better than a circuit diagram !! One picture is worth a thousand words. This will allow me to swop the modules to see if the fault follows. I've tried and tested everything else so this should identify the problem. I will post again when I get a result.

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2 months 2 weeks ago #22079 by Bumble2
Replied by Bumble2 on topic Old Rotax 912A ignition
Hi Rob,
I've now managed to swop the modules and the fault moves with the module. These are difficult to get hold of now, but a company in Europe will test/repair as needed so another month or so out of the air :(

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2 months 2 weeks ago - 2 months 2 weeks ago #22080 by RobSeaton
Replied by RobSeaton on topic Old Rotax 912A ignition
you can substitute the module for a 965-357 / 358 or 359
See SI-01-94

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Last edit: 2 months 2 weeks ago by RobSeaton.

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2 months 2 weeks ago #22081 by Bumble2
Replied by Bumble2 on topic Old Rotax 912A ignition
Thanks Rob, I may need that info if I can't get a repair. In case I need to do that, I have studied the circuit diagram between the Trigger switches and the input connector. It is clear which trigger goes to which module plug but it does not define which two poles of the 6/4 pole plug connect to. This is in contrast to the output plug which DOES define the positions. Do you think this is an omission or the electronics choose which trigger signal to use? I have studied this and purchased connectors to make up a transition loom and fell over at the first hurdle when I discovered the input positions undefined.

Your help is really appreciated on this, esp the link to the Heavy manual which I have downloaded.

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2 months 2 weeks ago #22083 by RobSeaton
Replied by RobSeaton on topic Old Rotax 912A ignition
the triggers give out a AC signal so it should not matter what way they are connected (same as the tach trigger)

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