On Fri, Apr 17, 2020 at 2:21 AM Brent Hilpert via cctalk <
cctalk at classiccmp.org> wrote:
On 2020-Apr-15, at 5:23 PM, Chris Zach via cctalk wrote:
Wonderful: A few weeks ago I forgot to turn off
my VT52 and left it
running for a day or two. Now the screen is filled with snow
and it looks
like the text is all over the place horozontally.
Any tips or thoughts on where to start looking to fix? The keyboard
seems to be
working as does the RS232 input (the snow on the screen changes
when the pdp11 talks to it)
Try turning the contrast or brightness up till the black level starts
becoming illuminated. Is the raster (the screen character field / framing
rectangle) stable?
If no rectangle or stable display field becomes apparent then as Jon
suggests it may be loss of sync, probably horizontal, and likely to be in
the monitor circuitry.
(Any affect from twiddling the H or V sync controls?)
If the raster is stable then it might be something in the character
generation pipeline (the character generator or the row pixel serializer),
or in the monitor video amp.
("snow" as a description leaves for a range of possible interpretations.)
There's always checking power supply levels to start with. In addition to
the +5, there's probably a +/-12 or -5 for the character generator.
Ian Primas knows a lot about these. (snark).....but def check the power
first, the large filter caps. I have a working VT50, which is similar but
not exactly. If you leave a terminal on for a long time and it dies,
that's a power issue or power related (caps resistor fried diode, etc.)
IMHO.