Main Board 3.57 TachIn problems

[wmahaffey]

I am using a 3.57 Main board for a system used on a '95 Lincoln 4.6 twin cam V8.

I have Jumper JP1 set between pin1 and pin2.
I have Jumper J1 set between pin3 and pin4.

I have a VR signal at JP1 of about 2 volts peak to peak, Looks very much like a Sine Wave.

When I put the scope on J1 the level jumps about 5 volts then is completely flat. No square wave.

I am checking with the processor removed and 12 volt power to the board.

Any suggestions as to what I am doing wrong?

Thanks,

Bill

[Matt Cramer]

Try adjusting the trim pots fully counterclockwise.

[wmahaffey]

Try adjusting the trim pots fully counterclockwise.

Matt,

No change. Still no square wave. I adjusted the POT in both directions.
Is there just one POT?

Thanks,

Bill

[Bernard Fife]

Bill,

There are two pots, R52 and R56. R52 is the hysteresis pot, and determines how low the voltage must drop before the circuit output drops to ground. Turning this circuit clockwise can reduce the effects of noise in the input signal. R56 is the voltage trigger adjusting pot. Note that on a 3.57 board these are 5 turn pots, unlike the 20 turn pots on a V3. main board.

On the 3.57 main board, R52 is near the center of the board, R56 is near the center of the bottom edge of the board (above the ".info" of the silkscreen.



You adjust them as described here: http://www.megamanual.com/ms2/vradjust.htm

Lance.

[wmahaffey]

Lance and Matt,

Got signal. I will make final adjustments after I get the car cranked.

Thanks again,

Bill