I've always used a screwdriver to turn the pots, but thanks for the tip.

I removed the pull-ups on the jimstim, and moved the primary tach jumper to the bottom two pins.

I set the DIP switch as shown and...NFG - still no tach signal.

The only reason I'm digging through schematics is to try to find where the RPM signal is dieing. It's good on the jimstim, it's good on the mainboard at TACHIN, it's visible (but low voltage) at the base of Q22. From there, it all goes to hell.

I've turned the R56 and R52 every way but loose and nothing seems to make any difference. So I have to believe that there's a component (maybe more), somewhere in the circuit that has crapped out.

Since I can't seem to figure this out, is there anyone anywhere that can take this "stuff" and make it work?

 

Ok, FWIW I've made some progress with this beast after a month or so of screwing around with schematics and measuring "stuff".

I've had to replace a faulty U7, a couple of wrong spec resistors and a shorted cap at C32. With all of that, I finally (sorta) have a sync signal. The problem now is that the RPM signal "bounces" (i.e. oscillates between zero and whatever the setting is on the pots on the jimstim). It does this at every RPM value from a few hundred to 3600 RPM where something odd happens.

At approx 3600 RPM the output to TunerStudio will either drop to zero and stay there, or - with a minute turn of the fine control - jump to 3600 and start bouncing again. This is progress, of a sort.

The story continues...