I'm back. Sorry about letting the tread go cold, but we got busy in the field. If I have new eyes and brains here, the old thread is here: Combine grain loss sensor questions | All About Circuits . We used the combine to cut rye, and I managed to catch (as a couple people mentioned) that I had lost continuity in the shielded signal wires. They were showing somewhere between 20 and 50 ohms. I'm guessing that's not good for a signal wire, so I luckily happened to have some shielded cable on hand and replaced it all the way into the cab. I would guess there may have been some corrosion, but that did not fix our problem. So, we know we have 8V and a good ground to the sensors and a new shielded cable running to them. If we can't find a problem with the sensors, the problem could be the module in the cab which I was told by a mechanic was very uncommon (as in he had never seen it). I bought an oscilloscope and power supply as suggested, and an attempt was made at taking some measurements. With 8V applied to the circuit, the voltage between R1 and R5/T1 (sorry if my labelling is confusing) was 1.8-2V. From R5 to R4 voltage was 600mV. After C1/T1 I could not get any voltage reading. Tapping the piezo I could not get any response anywhere in the circuit with 8V applied. It's very possible I do not have the scope set correctly to catch the signal (first time I've used one). However, with the power supply disconnected and the scope probe ungrounded I was able to get a 60 Hz signal when tapping the piezo (also showed negative 1.6-2V but does that mean anything if measuring from a single point?). Again, I am not an electrical engineer; I am a farmer who greatly appreciates your help. I was flattered by the response I received on my last post. You should be proud of your community. Thank you again, Robert.

 

Okay with power connected, put the scope on AC (try 1V cm) and check the points marked on the diagram, scope check is to test the signal input from the sensor, scope probe is to check the output to see if you are getting a signal. Tap the piezo with your fingers and see what happens.

 

I couldn't get any reading from the scope check position. I couldn't get a reading from scope probe with my fingers. When I struck it with a metal pick I have here I managed to get around 2 to 5Hz but the signal for each strike only lasted maybe 100 to 130ms. Is 'trigger holdoff' a relevant setting? It's set to 1 microsecond now, and I'm not sure I didn't accidentally change it when I was trying to learn the settings.