Hardware revlimiter fried

[eric_f]

Hey everyone
So yesterday I got my MJLJ in the mail, awesome, so I promptly assembled it and tested and all works fine, SWEET!
I then go to install into my car and get everything hooked up and try to start, no dice, hmmmm, check spark, nothing.
Today I open up my MJLJ and smell the wonderful smell of burnt electronics, oh shit.
So, as you can see below the mosfet fried.
I'm wondering what might cause such a thing to happen?

Thanks
-Eric

PS, the MJLJ I assembled, but the revlimiter was already assembled, I just wired them together
Edit: While looking around I noticed the limiter is missing its transistor, WTF? Could that be the issue? Nevermind, the small one is there and the big one is for kit builders.

[NITROPIXIE]

Jesus

That is one fried chip, avalanche breakdown comes to mind here. Are you sure the wires were the correct way round on the board??

I'm sure we can get it sorted for you though.

Ryan

[brentp]

Ouch!

Clearly the mosfet was overloaded with too many electrons. Try connecting the coil power to conventional +12v, as you would without the rev limiter. Do you get spark? Does the system work, aside from rev limiting?

As for the rev limiter, double check the +12V, coil, trigger and ground connections. did you get any of these mixed up?

[eric_f]

I will try without the revlimiter after work today.
I have checked, double checked, had friend check, my wires are all in the right spot

[NITROPIXIE]

Well if you send me the board i may be able to resurrect it if the tracks aren't too damaged and i can find a replacement chip??

[brentp]

Keep us posted! We'll get you sorted out!

[Funky Diver]

Might be better sending to Brent as Eric is in Surrey,Canada, not Surrey, just off the M25...

[NITROPIXIE]

Doh well spotted that man.

Shame they couldn't think of more original names when went across the pond all thse years ago.

[eric_f]

Well the traces aren't fried, so that's a good start. I will try and source the part locally instead of paying $10 to have it shipped from Digikey.
I'm just worried that if I replace the mosfet that it will fry again as nothing has changed.

[brentp]

Keep us posted on how well it runs sans rev limiter. Under normal operation the mosfet should not even get warm while running. If you can't find a replacement part drop us an email at sales (at) autosportlabs.com

[eric_f]

Ok, well it runs, for the first time in 5 years it runs. However it's backfiring out of the carb on cylinders 1/2.
I have switched the plug wires around and it seems to be the best right now, but still not good because of the backfiring.
The carbs might be out of tune so I guess I should play with them and see if that helps or not. I'm also using the default map, which I will switch to one from dannyp as the car is a '68 VW Beetle.
So that leaves me with the issue of the rev limiter, I don't know exactly what is easiest/best for me.

[brentp]

Thanks for the update- Is it running smoothly on all cylinders, or is it running rough?

[NITROPIXIE]

Don't forget has a different firing order than a straight 4 so the ht leads may need to go in a different order. If you have a timing light to hand it should help you check each lead is firing on the correct stroke, at the right time of course.

[BRUCEROE]

If its not a straight 4, what is the configuration? On my 2 cyl I used a V8 EDIS, because the 90 degree angle between cylinders was the same as a V8. Bruce Roe

[eric_f]

For the firing order I found this. So my firing order is 1-4-3-2 and the EDIS is 1-2-3-4, so in theory I switch the 4 and 2 and everything should be savvy. However, backfires like crazy and won't start.
I switched them around (I can't remember what exactly they are at right now, I'm at work, I'll see if I can get some info) and it runs pretty well, it does seem to miss a cylinder fairly often, it will run fine, then miss. So that tells me a plug isn't firing, probably a connection somewhere
I do have a timing light, I'll just have to dig it out and see what it says, if I can remember how to use it