Osborne OCC1 problem
Roy J. Tellason
rtellason at verizon.net
Thu May 15 21:04:15 CDT 2008
On Thursday 15 May 2008 19:48, Ade Vickers wrote:
> 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...
I'd have kept it for spare parts, at least -- inside they're basically the
> > > Measured with respect to Earth (green wire, goes everywhere
> > > including 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'd find a convenient ground point. Beside the ones on the power supply there
are no doubt others on the mainboard and at least one on that edge connector.
> > > 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
> > transformer.
> > 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.
A bit of a contrast to my Exec, which has a fan in it, that I replaced with
a slightly stronger (AC) one. :-) That was a retrofit done by several O-1
owners that I know of that wanted cooler and more reliable operation. All
you need to do is replace the bit under the handle with one that has the fan
opening, at least on the gray case.
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
Information is more dangerous than cannon to a society ruled by lies. --James
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