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Sharp CE-122 printer motor running too fast?
09-18-2022, 10:22 PM
Post: #8
RE: Sharp CE-122 printer motor running too fast?
Fixed it!

The timing mechanism is just a simple magnetic speed sensor on the end of the drive shaft, with two timing pins on the ribbon cable. I'm assuming it creates an AC waveform across these two pins as the motor runs - I'm no EE though. Smile

If you look at the circuit diagram, you'll see that each side of the timing signal has a 330 pF (filter?) cap to ground. The one on the right had some white gunk around its legs, though I don't have any idea where it came from. There wasn't any sign of leakage from any components - old crusty flux residue of some sort maybe? Anyway, I cleaned up around the legs of the two caps, and it seems to be running fine now. That certainly explains why the PCU was only seeing half of the timing signals if one side was partially shorted to ground!

I need to find some fresh(er) ink ribbons though. 40-year-old new-old-stock ink leaves something to be desired.
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RE: Sharp CE-122 printer motor running too fast? - Dave Britten - 09-18-2022 10:22 PM

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