jeff@cjsa.WA.COM (Jeffery Small) (02/04/89)
First, I want to thank everyone who responded with helpful hints as to
what might be causing the wavy screen display on two of my 3B1 machines.
For those who may be interested, I have summarized below, the ideas which
I received and the results I achieved. It has taken so long for me to
respond because I have taken one of these machines apart six different
times in my quest to effect repairs. I managed to get one unit working
fine. The second one still has the wavies.
In no particular order, this is my short summarization of the suggestions
which I received concerning the problem:
- Clean the pots (controls on the rear of the monitor seen when the cover is
removed) with tuner-cleaner, rotating them back & forth, making sure that
they are returned to their original position.
[I didn't think this was related to my particular difficulties, but in a
moment of frustration I did clean the pots. This didn't fix my problem
but as an interesting side note, when I was turning the video intensity
pot, my screen all of a sudden went blank. No amount of adjustment
could restore the screen display. So, I rebooted the system and
everything was working fine! Anyone got an explanation for that one?]
- Problem may be caused by fluorescent lighting where the 60-cycle flux
from the fluorescent light is out of sync with the refresh rate of the
screen.
[I think this would cause flicker, not the "Pepto-Bismol"-type wave
which I was experiencing. Anyway, no fluorescents here and the worst
offender is illuminated fully by natural daylight.]
- Check for strong magnetic fields adjacent to the monitor which could
be causing the distortions. Apparently, two UNIX-PC's set close to
one-another can cause this condition.
[That wasn't it.]
- Check the solder connections where the power supply cable connects to
the motherboard.
[Have to admit I didn't re-solder these connections 'cause you have
to remove the motherboard to do it. I did check the connections
and they all appear (from top inspection) to be solid.]
- Check the connectors - especially the power supply connectors to make
sure they are tight and free from oxidation.
[I took apart every connector that could be possibly related to this
problem, cleaned them and crimped or bent the connection tongs to
insure a tighter fit. This seemed to improve the situation for a
a very short while on one machine, but soon it was back to its old
self :-( I checked the connectors twice, too. It was probably
wishful inattention which made me think things had improved.]
- Clean the metal grounding strap inside the monitor hood which sets down
and grounds with the winchester shield cage.
[I cleaned, tightened and rebent this strap and cleaned the top of the
winchester cage. When I put one of my units back together, the problem
was MUCH WORSE! This was good - I was on the right track. I took
the machine apart, fiddled with all of this stuff again, put it back
together and I haven't seen the problem there again :-) But ....
this didn't fix the second machine.:-( I even installed a grounding
wire between the strap and case with no effect. This idea came from
an AT&T employee who reported that this grounding strap problem has
appeared on many machines and generally a good cleaning solves the
problem. Thanks!]
- Monitor has gone bad. Buy two new ones for $50.00!
[May just have to do this if it's not the power supply.]
- Either the external AC power is fluctuating or else the power supply
is shot and it is putting out fluctuating voltage.
[I need to borrow a scope to check this out. Still working on that.]
SUMMARY:
One down, one to go ....
--
Jeffery Small (206) 485-5596 uw-beaver!uw-nsr!uw-warp
C. Jeffery Small and Associates !cjsa!jeff
19112 152nd Ave NE - Woodinville, WA 98072 uunet!nwnexus