This same problem started happening recently with my 582 BlueTop (100 hours). At 3000 rpm, one mag switch dropped ~100 revs, as usual, but the other mag switch caused the tacho to read ~400 rpm lower, but with no corresponding drop in engine note. WEIRD!
I thoroughly checked the ignition wiring: all connections good, resistances of ignition coils OK, etc. At cruise RPM (5800), flicking the "problematic" mag switch dropped the tacho by 2000 rpm (!) with no change in engine note. Suspecting a ground fault, I re-wired all earth connections to a single engine attachment lug, but this made no difference. Swapped in a new set of plugs (getting desperate); no difference.
Local (New Zealand) "expert opinion" said to simply ignore the erroneous tacho reading, i.e. this "just happens" with Rotax engines, nobody knows what causes it, and there's no fix. As an electronics tech (in a past life), I thought that was complete bollocks, but carried on flying.
A couple weeks later, when taxiing out to the strip, quite suddenly there was a loud "static" noise coming through the headphones, like severe RF interference. Flicked all the switches, etc, to no avail. The engine was running fine, so I did a few circuits (hoping the problem would right itself).
After landing, I attempted an engine start but the battery was now fairly flat (I think the landing lights were inadvertently left on). I got the engine running (spare battery) and checked the rectifier output -- no voltage; should be around 13.8 VDC. Likewise, no AC output from the lighting coils, and the winding appears to be open-circuit (should be ~250 ohms).
It seems way too coincidental that all these electrical symptoms turned up one after the other, although the 'charging' and 'lighting' circuits are electrically independent.
At this point I suspect a blown lighting coil, but I've not yet pulled the flywheel to inspect the windings, etc. That's the next step...
Why would a perfectly good set of coils suddenly burn out for no apparent reason? There's no point in replacing the coils if some unresolved problem causes failure of the replacement (costing NZ $600).
Has anyone else experienced similar issues? Any ideas what could be going on? And how to fix???
