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OK. Upon further investigation - please, I hope somebody will read this and help me to get on the right track! - the opto-coupler on my controller board (labeled 'U6') ... the input ... measured against the digital ground - looks good. The PWM signal from the ATMEGA pulls pin 3 'low' with each of the peaks (well, from 5V at zero throttle, to 3.5V at full throttle) - so that places a 1.5v potential across the photodiode on the input side and makes it conduct and pass the signal to the output diode.
Here's where the problem is, I think. The output diode, when 'On', should pull pin 2 of U7 to ground, otherwise it should be +12V with respect to the power board's ground, right? It's not. It's 0.7V at zero throttle and 0.29V at full throttle. There is no short to ground at R16 or between pin 6 of U6 and pin 2 of U7.
I think the input to pin 2 of U7 should be basically an 'upside-down' ATMEGA PWM output with a peak-to-peak voltage of 12V, is that right?
I'm thinking right now that U6 is bad and I have to replace that.
Anybody concur? Am I reading this all wrong?
Thank you sincerely,
Michael
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