A couple of days ago I mentioned I'd discovered a workaround for Epson
SD320 or SD321 spindle motors that stopped after a few seconds because
the protection circuit was tripping...
Well, one came back to bite me.
I spend the afternoon looking at the other drive in the TF20. I'd changed
the resistor I mentioened and put the motor back in place. Hooked it up
to the bench supply, and would you beleive it stopped after a few seconds.
So out it came again. The bare motor stopped after a few seconds too, and
the protection cicrcuit was certainly being triggered (the base of Q33
was at about 0.6V). I noticed a leaky electrolytic, so I changed that, no
improbement.
So I decided to totally disable the protection circuit by removing the
300k feed resistor. You guessed it, the darn thing still triggered, there
was still 0.6V on the base of Q33. All that's connected to that point are
a resistor to ground (the one I'd reduced to 56k), a capacitor to ground,
and the base itself. I removed all 3 components. OK, the mtoor now ran
(so the rpoblem was in the protection circuit). And there was nearly 9V
on the base connection for the transistor -- a point that had noting
connected to it.
You guessed it. some of the gunge from the faulty capacitor was causing
electrical leakage on the PCB. I could read 100k of resistance from the
isolated track to the nearby 9V supply to the CX065B chip. I took out a
few more components to get to the PCB surface, then really cleaned it up.
And then I was getting over 30M leakage.
Put everything back, and it seems to work....
-tony