Re: Display weirdness with IIe?

[Rubywand <rubywand@swbell.net>]

Gareth writes ...
> 
> The composite video output (PAL) on my IIe is acting strangely. When
> in "normal" text mode, the background intermittently changes colour,
> from brown-ish to solid black to a kind of slightly red-ish. It
> especially happens in sync with disk drive operations.
> 
> However, when in a graphics mode (e.g. playing Choplifter), there's no
> problem at all - the colours remain rock-solid.
> 
> Does anyone have any ideas? It's *definitely* not the monitor - it's
> fine with any other composite video source plugged in.
> 
 ....

     One way or another, this does sound like a power-related problem.

     One way would be a power supply connector which is making poor contact
on one or more pins (or a power supply with a damaged output).  The
additional current drawn by an active drive might pull down voltage enough to
shift logic levels on some IC's and mess up the Text display.

     Cleaning the power supply connector and 're-crimping' the socket pins 
(or slightly squishing the plug pins)  for a tighter fit could help.


     Another way power could be involved would be a poorly socketed IC--
probably a multi-function controller or a multi-gate IC which has gates used
by video circuits and other gates involved with the disk drive interface. A
poor power supply contact on one of the IC pins (e.g. Vcc or GND) with the
socket could lead to interaction among separate logic gates on the IC.

     Pulling, cleaning pins, and resocketing each socketed IC usually fixes
the above.


     There are lots of other possibilities. Like, an IC may be defective. Or,
something may be drawing more current than it should (or someting is creating
a partial short).  Unless you've had a recent serious surge on the AC line or
someone spilled Coke on the keyboard, the stuff mentioned earlier seems more
likely to lead to a fix.




Rubywand