In SX Microcontrollers, SX/B Compiler and SX-Key Tool, dkemppai wrote:

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Hi all,<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana"> <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Had another SX blow last night. The "VPP Generation" Error popped up again. Checked OSC1 to ground, and it was 183 Ohms! So, I'm thinking WTF!  I replaced that SX, and ALL of my the problems went away. I could program and debug at 5 volts, and 3.0 volts...<o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana"> <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Then I started checking a few things. I threw the fluke between my scope ground and PC ground. .002 volts max, .001 volts min, so that was acceptable. <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana"> <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Then I threw the meter between my scope ground and my power supply ground. Same story, very low voltage. Then I turned the power supply on. And I got a peak measurement of 31volts, to my scope ground! Now something to start looking at! So, I throw the scope probe on the supply ground, and I see a 60Hz 76Vp-p signal. Ah-HA! Power supply is now suspect. The ground lead of the supply isn't ground, it's floating! Apparently it's meant to be a floating supply! Except, that the thing appears to have capacitive coupling to the AC Mains (through the transformer, probably?!?). For grins I measured the AC current between the grounds, 13uA (very small). So, my solution was to tear into the supply, and place a 10uF 100V poly cap from the supply ground to earth ground. The measured voltage is now <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:place w:st="on"><st1:PlaceName w:st="on">2mV</st1:PlaceName> <st1:PlaceType w:st="on">Peak</st1:PlaceType></st1:place> to peak between the grounds. (The capacitor solution will allow me to float the supply if necessary, yet it swamps the leakage capacitance in the transformer...  ...I may add a bleeder resistor to ground tonight.)  A quick calculation shows that the transformer capacitance is on the order of 270pF...    

<SPAN style="COLOR: black; FONT-FAMILY: Verdana"> <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Anyway, I'm guessing that the high voltage was stressing the chips, and pushing them close to failure and they wouldn't work at 3.0 volts. (Still seems a bit weird, as overvoltage failures are usually catastrophic). It looks like, Eventually the chips would fail, then nothing would work...   ...<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Overall, things seem to be working again...    ...until the next weird thing...<o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana"> <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">Thanks again for all who replied, and helped!<o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana"> <o:p></o:p>

<SPAN style="COLOR: black; FONT-FAMILY: Verdana">-Dan

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