Running fine, now No RPM

[CorradoVR6]

I have a VR6 Corrado with a V3.3 ECU. Car has ran flawlessly for 2 years. Last week I drove the car 700 miles in two days with no issues. The next day I try and start it up and no RPM signal despite having no changes in hardware or software. Laptop connects to the ECU fine, can see map, throttle position etc all changing, just no RPM on cranking.
To troubleshoot it I have tried 3 different crank sensors including a known good one. I read 820 ohms on pin 1 and 2 of my VR style crank sensor. I also measure 820ohms at pin 26 and 27 of the EC36, so I know continuity is good. P259 looks to be functioning correctly, I checked 3 channels and all could drive their output low (do I need to check the rest of the channels?). I don’t have the secondary trigger circuit to try firing up with that.

ECU is running 1.2.31. VemsTune is 1.5.57

I’m at a loss as to what to look at next. Is it common for U11 to crap out? Any advice is greatly appreciated!

Edit: added firmware and VemsTune version

[gunni]

Are you able to scope the input to the ECU ?

[CorradoVR6]

I am able to get hold of a scope tomorrow. I have added a couple of wires to my board so I can check the signal before and after U11 also.

[CorradoVR6]

Pretty positive U11 is dead. I have a nice 4V peak to peak sine wave going into pin 3 and a flat line coming out on pin 12.
I think I will be ordering a couple LM1815 chips and probably some P259 just for future problems.

[CorradoVR6]

U11 replaced and I have an RPM signal once again.