Finding Common Ground

From: Bo Zimmerman (
Date: 2000-01-23 20:04:00

Hello all.  

I spent a few hours this weekend playing with my P500, trying to figure out
why it is misbehaving.  The symptom is that no video signal appears to be
forthcoming from the machine -- at least my PAL/NTSC converter is not
reporting a valid PAL signal from it, and blind disk commands give no
response.  The machine could be completely dead, I don't know.

I Have converted the power supply from 220V->110V using a spare B500 PS, and
that changed nothing.  I've checked the EPROMs, and they are fine.  I've
swapped some of the common chips (processor, etc), and thats no help.  The
seller swore to me the thing worked when it left his house, so I am quite

Today I checked the voltages on everything, and it looks cool for the most
part.  I did discover something strange, however.  There appears to be TWO
grounds.  One that runs along the AC line (from the wall), and one that
runs along the DC line.  I've never noticed this before and am wondering --
is this normal?  Is it good?

  I figured there might be someone more familiar with electrical stuff on
this list to help me out.

  I appreciate any replies on this matter though,

   - Bo Zimmerman

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