16 May
2008
16 May
'08
12:24 p.m.
What's happening is a corruption of the display,
rather than an
adjustment
A more accurate fault description would be helpful...
When the screen is showing static information, and the disk(s) are not
running, then the display kind of looks like it's got a h-synch problem. Or,
try this: It looks like there's a strong right-to-left motion blur. That's
still not 100% accurate, but I'm no artist & trying to describe it is beyond
my ken.
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
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?
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.