Osborne OCC1 problem

[Roy J. Tellason]

On Thursday 15 May 2008 19:48, Ade Vickers wrote:
(Snip)
> Maybe I should monitor the PSU voltage on the 'scope while the machine's
> booting - I hadn't thought of that one. Could be interesting - the bulk of
> the computer is currently upside down on the bench to make it easy to
> access the bits of the PSU I need to probe... if the 5v line is flapping
> about, this could cause the digital effects. Mind you, the fact the machine
> boots properly indicates that the logic side of the machine is working
> fine; and I'd have thought the disk drive would be more sensitive to 12v
> fluctuations than the monitor?

The drive only uses the 12V for the spindle motor,  I think,  but do check 
them both.

And clean the edge connectors for the drive ribbon cable too,  that's been a 
trouble spot in my experience,  what with them running power through the 
ribbon cable.

> > Does this machine use a 6845 or similar for hre video timing
> > chain?
>
> Dunno, will look tomorrow (err, later today).

I believe so,  though it's been a long time and I can't be 100% certain of it.

> > If so, mis-programming that will cause apparent sync
> > problems. So the fault could bever well be proscessor, ROM,
> > or bus related.
>
> Bearing in mind the machine boots, and works behind its corrupted video
> output, would that necessarily eliminate any of those parts from enquiries?

Not necesarily.

> > That's why I'd start by looking at the horizotnal sync pulses
> > when you have the lines and when you have a good display
> > (even if the machine has crashed). If they're the same
> > timing, then the fault is monotor (or PSU?) releated. If not,
> > then the video timing circuitry is palying up _or being
> > mis-configured by software_
>
> Gotcha - will look at that tomorrow.
>
> > > I'll look for it... the monitor circuit board is quite well labeled; but
> > > I'm not sure if the connectors themselves have individually labelled
> > > connections. 
> >
> > Sony were sometimes kind enough to label connector pins,
> > supply lines, CRT pinouts, etc in the slikscreen, few other
> > manufacturers were.
> >
> > If it is a standard pinout, then the connections are
> >
> > 1 Ground
> > 2 One end of the contrast control
> > 3 t'other end of the contrast control
> > 4 Slider of the contrast control
> > 5 ground
> > 6 Hsync
> > 7 +12V power input
> > 8 video input
> > 9 Vsync
> > 10 ground
>
> I've not counted the pins, but one thing - where's the brightness control
> go? The machine has external (to the monitor) controls for both contrast &
> bright; as well as trimpots for both on the monitor PCB itself.

Darn,  I *really* need to find my schematics on this stuff...   :-)

(Snip)

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