Revs now reading very low

richardk · Post by **richardk** » Sat Jan 10, 2009 11:52 pm

Just to give you a bit of background, my megajolt has been perfect for about a year, and I recently got a Jaw kit to monitor fueling, anyway I have managed to break my jaw doing what a few people have done http://14point7.com/forum/index.php?topic=79.0 but ever since blowing the atmega8 micro on my jaw my rev counter has been reading very low, it seems to read correctly in the config software and the shift lights seem to be coming on at the right revs so can anybody point me to a component that could have possibly got damaged on the megajolt by connecting the rev counter wire to a micro on the jaw unit that was only expecting 0v - 5v, needless to say it didn't like it.

Any help would be greatly appreciated, I do seem to remember having to make a little circuit on installation which if I remember right was a couple of resistors and a zener, could these have got damaged or is it more likely to be something on the board itself, don't know if that helps at all but thought I'd come clean

Thanks

Rich

Post by **brentp** » Sun Jan 11, 2009 1:33 am

Hi Richard,

Without knowing the wiring configuration you have between the MJLJ, EDIS, coil pack and JAW -specifically, how it was wired when the problem occurred, it's hard to say how a damaged atmega8 on the JAW might affect the Megajolt.

Where do you have your rev-counter connected? is it to the TACH_OUT on your MJLJ (I presume it's a V3)? IF so, with the V3 hardware a better tach source is the PIP signal or using the classic diode circuit, sensing right off of the coil packs.

The fact that the MJLJ is showing the correct RPM is a very good sign. If the MJLJ is also correctly controlling ignition advance I would say your MJLJ is in "pretty good" health.

Regards,

richardk · Post by **richardk** » Sun Jan 11, 2009 9:09 am

Thanks for that Brent, yes I'm using the classic diode circuit right off the coil pack, now I've had time to sleep on it, realised that having 15v now on that tach output isn't quite right, this is sort of confirmed when I switch on my lights the rev display on the tachometer raise quite alot, still not upto where it should be, maybe this will give you a clue as to what the problem is. Am I correct in thinking the tach range should be 0 - 12v?

Thanks

Rich

Post by **brentp** » Sun Jan 11, 2009 9:17 am

Hi Richard-

Hard to say! Is everything running OK other than the rev counter?

You may want to try running your rev counter off of the PIP line (make sure you disconnect the rev counter from the coil packs!!!)- that may give you better results. Possibly your rev counter might need repairing?

richardk · Post by **richardk** » Sun Jan 11, 2009 11:27 am

OK, I've stripped back the diode circuit in my loom and the zener was shot,replaced it and I'm now a happy bunny again. Just need to fix the Jaw

Unfortuanatly the creator of Jaw isn't as quick as yourself in replying to requests for help.

Thanks again Brent for creating such a superb bit of kit over the last year have been delighted with it.

Cheers

Rich

Post by **brentp** » Sun Jan 11, 2009 7:42 pm

Happy to help- and please spread the good word!