Blown my MS3 ???

[hobieboy]

I had been chasing a problem with getting the engine to run beyond idle (http://www.msextra.com/forums/viewtopic ... 34&t=60636) and decided to go back to step 1 to validate VR signal.

A question about what I should see if I probe VRIn and VR Out - with key turned on but not running (beyond cranking), should VR Out be reading 0V ?
I didn't take notice before but as soon as I power up MS3, VR Out now goes to ~3.3V... does it mean I have blown something in the VR conditioner circuit?

[billr]

I think VRout should only have two possible states: either 0V or 5V. Do you get 3.3V there when the daughter-board (MS3) is removed (or jumper from VRout to tachin is removed)?

Edit: I'm talking about when the engine isn't running or cranking, not rotating at all so no input at VRin.

[hobieboy]

I may have answered by own question with my limited electronics skills... If I understand correctly the VR conditioner circuit output is fed by an Op-Amp (MC34072AP) so as long as the output square wave (saturated voltage) is higher than logic 1, it is ok for the IRQ-1 that it feeds. When the input (VRIn) is held at ground (zero-crossing) then it triggers output to high.

I verified that MS3 is still generating proper VROut square waves so I guess I didn't blown anything up

[billr]

Yeah, sounds like it is OK. Your thinking about the op-amp operation is essentially correct. There are threshold and hysteresis considerations (the two magic pots), but the the output should be either "on" on "off".