Osborne OCC1 problem
javickers at solutionengineers.com
Thu May 15 18:48:23 CDT 2008
Roy J. Tellason wrote :
> Hm, could be I'm mis-remembering slightly here. Or it could
> be used in later stuff. I recall seeing only one or two of
> the tan case units, most of them were the later ones.
I sold my non-tan cased Ozzie, on the basis it wasn't rare enough for my
liking! Of course, that one worked perfectly...
> > Measured with respect to Earth (green wire, goes everywhere
> > to the mainboard). As far as I can tell, this acts as GND for the
> > whole machine?
> Shielding more than anything else, I'd guess.
OK, that would make sense. In which case, I'd expect the differential
between pins 3 & 4 to be approx 5v, but will confirm tomorrow.
> Even still, it shouldn't be fluctuating either.
My mistake - there was no fluctuation, except in the optics of the sensor
(me & my eyes). The voltage output was a perfectly flat line (except when
the 'scope sensitivity was turned to 20mv/cm, at which point I could just
about see some rectification effects - but getting the 'scope to trigger on
the peaks was really hard work; it's a pretty flat line.
The signal on Pin 3 (-0.1v I guessed at) was a little noiser, but seemed to
be random noise. Having said that, I didn't "zoom in" on it so much.
If, as you imply, Pin 3 is GND and Pin 4 is +5v; then the difference between
those two is much closer to 5v than between Pin 4 & Earth.
> > Your assistance is much appreciated. I've still got to try Tony's
> > suggestion of checking out the H-sync signal, but I need to
> find it first...
> It'll be on that connector on the front, and prety obvious
> which one it is because of the repetition rate, as opposed
> to the much lower rate for the vertical sync, and the much
> erratic nature of the video. And if it's *way* off in
> frequency or changes a lot or has a lot of jitter than we're
> probably looking at the power supply not being right.
Should I probe these with reference to the GND (Earth/shield) or the 0v line
(pin 3, as above)?
> > I shall consider it - is there any (non-destructive: I know you can
> > pump 240vac into it, then when the magic smoke escapes
> conclude it's
> > broken :)) way to test an electrolytic cap?
> With some equipment, yeah. The least I'd want is to use an
> isolation transformer to plug the computer into and then
> scope across the main filter caps and see what you get, but
> I wouldn't care to mess around in there without an isolation
> If they're bulgy on top they're bad.
They look brand new TBH. Not even any dust on them (probably because the PSU
is mounted component-side-down in the case). That, and the case itself is
pretty tightly sealed when the unit is assembled & closed up.
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