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STE no reset on power up issue fix

Posted: Wed Sep 25, 2019 9:42 pm
by exxos
This seems to happen very often now, but not just on STE machines. Where the machine doesn't reset "from cold" or doesn't reset on power on at all. Normally the work-around is to press the reset button and machine boots as normal.

There have been various reports of this when adding boosters, or changing the PSU etc. I had this issue yesterday while using a stock machine to test simms.

The reset circuit is pretty rubbish to start with, but like always, bad caps are mostly to blame, but not only that, the caps seem to be wrong values as well.

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The quick fix I did (as others have done and confirmed) is to solder a 22uF across C100 (for approx 33uF total) . Upping the value of C102 does nothing. In fact it seems C100 *should* be a higher value than C102, but the circuit shows C102 as larger. I haven't yet had time to look into this more.. but this is what I did..

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I would suggest changing C102 for a new capacitor, keeping 22uF as the value. C100 replace with a new 47uF capacitor. Voltages between 10V - 63V are typical. This will likely solve a lot of reset issues on the STE.

As reset circuits are similar with STFM, Falcon, MEGA etc, this fix will likely solve reset issues on those machines as well.