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The mkiv Supra Owners Club

speed converter help


Suprab1

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Has anyone ever tested a failed speed converter? I'm getting a fluctuating voltage both sides of my speed converter but no speed reading in the car. But here's the strange part when i test the speed converter for resistance it's showing open circuit. Now i'd expect open circuit on a failed converter but why am i seeing voltage both sides?

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I've never tested one, but I do know that the speed signal is a square wave pulse, not an analogue signal. Hence, to convert from kph to mph (i.e. divide speed signal by 5/8), it won't scale the voltage like a standard op-amp circuit would, but it has to fiddle with the frequency of the pulses, and presumably leave their amplitude untouched.

 

Not sure if that helps, but if you're testing using a multimeter, the pulsed signal might confuse it.

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Are you measuring the voltage with a standard digital multimeter? If you are, I think you'll struggle to do any diagnosis, and you could get any kind of (false) readings. Multimeters can measure either a steady analogue voltage, or a 50Hz alternating voltage (maybe assuming a sine wave): i.e. mains voltage.

 

What input are you feeding into the converter for your test? To do a good test you'd have to feed it a pulse of known frequency, and measure the input and output with a oscilloscope.

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Yeah just a multimeter as i don't have a scope. I was just testing the signal wire from speed sensor in gearbox & hand turn the rear wheel. When i do this i get voltage fluctuating between 0-11v then after the speed converter test it there & i'm getting similar readings. My converter is down about 1 foot away from the speed sensor, it's about the size of a sim card & has an input, output, positive & negative. This is the first time i've done any work with these converters, just not 100% with them.

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