17 May
2008
17 May
'08
8:34 a.m.
Tony Duell wrote:
Hmm, yes, I can see how that might cause problems...
I could run the picture through an ascii-art generator if that would help?
;)
I've 'scoped the 12v & 5v lines both in "steady state" and
"booting" now;
both are remarkably stable (a bit of noise on the 5v line when booting, but
in the millivolt range. The 12v line rises slightly when you unplug the
monitor, which is not a big surprise since the monitor will, obviously, be
drawing power.
Basically, these readings over-ride any which have gone before....:
12v line = 12.75v, no discernable change or noise when booting or stable.
Slight rise (unmeasured) when power to monitor is withdrawn.
5v line = 5.4v, dropping to 5.3 between Vss and Vcc of one of the logic
chips. Generally pretty stable, some slight noise whilst booting.
There is NO difference between the voltages when the machine is running
(video blurry) or crashed (video stable).
Hsync remains rock solid whether crashed or running. I couldn't accurately
gauge the pulse width as I don't have a signal generator to calibrate the
'scope with.
Well, the
video I linked to is about the best description I could
think of...
Which is not a lot of help to those of us with a text-only
display, and to whom 'video recording' means a Philips N1500
or V2000 tape... When the
machine is booting from disk, the screen flashes
and flickers
like a mad thing: But as I say, it seems to be
*digital*
noise rather
than analogue. But with some analogue effects
thrown in for
good measure...
That sounds _very_ like PSU trouble to me. The disk drive
motors take significant current, and that's pulling one of
the supply rails down and casuing all sorts of prolems. The average voltage of the supply line, as measured by
a
mulitmeter, may not change much, but a 'scope would show
masty dips in the voltage
None visible.
Well, it might be a non-standard pinout, then :-(. Or
is
there a separate
3-wire cable for the brightness pot? I've seen that several times.
Brightness goes to the monitor. The contrast, I've discovered, is just the
Video Out signal passing through a variable resistor. Simple, really...
Cheers,
Ade.
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19:42