| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1118.1 | Try reseating chips first | YNOTME::WALLACE | | Fri May 10 1991 13:54 | 10 |
| I haven't had this particular problem, but the first thing to do is to rule
out loose chips. Open up the ST and push down (firmly) on all the socketed
chips. Uslualy you don't feel them move but sometimes you hear them creek,
that's all it takes to fix a lot of ST problems.
I've got to reseat the chips in my Mega this weekend in order to get rid of
some black verticle stripes. The problem shows up about every 6 months after
reseating.
Ray
|
| 1118.2 | Tune the TV ? | BRUMMY::LOXTON | | Mon May 13 1991 11:32 | 8 |
| That sounds like a sync problem
Are you using a TV,If so it may just need tuning properly.
Otherwise,the video shifter chip is in a socket underneath a metal
case.Try giving it a push home.
Brian.
|
| 1118.3 | I agree - poor sync | PRNSYS::LOMICKAJ | Jeffrey A. Lomicka | Mon May 13 1991 16:06 | 1 |
| Try contact cleaner on the 13-pin video jack and plug.
|
| 1118.4 | more questions & suggestions | GIDDAY::HIRSHMAN | GIGO: Garbage In, Gospel Out | Tue May 14 1991 02:35 | 20 |
| You don't say so, but I assume you're using an SM124 or SM125 mono
monitor on your STfm - is that right?
Anyway, it sounds like you're getting crosstalk between the video, sync
and audio signals, most likely due to a high resistance connection
somewhere in the signal ground path to your monitor. Jeff is right (as
usual) - the video socket and plug are the prime suspects. If you
can't see any corrosion or grunge deposits on the contacts and cleaning
them doesn't help, then it might be a bad solder joint on the socket or
a flakey monitor cable - especially if your connectors got bumped or
yanked on recently.
Do the symptoms change when you gently wiggle the connectors or flex
the cable? If you have more than one monitor, do you get problems on
both? Also, what do you get if you hook up a TV to the RF output socket?
BTW, re .1 and loose chips: have a look in 1013.9 for a simple mod to the
square "QIP" sockets that seems to be a permanent fix.
Bret.
|
| 1118.5 | Extra! Extra! Read all about it... | WARNUT::YATES | Double Glazed DECWindows are best | Tue May 14 1991 11:53 | 23 |
| Okay...the story so far, and more information...
I have tried opening up the machine, and giving all the chips a good
push (whilst well grounded of course), and it HASN'T fixed the problem.
The chips did all give a creak every now and again, but the problem is
still there. I have however found that it gets worse the larger the
windows are on the screen. If I create a small(ish) window the the
display is close to completely stable - only the menu bar at the top is
slightly skewed. BUT if I then enlarge that window then the display
goes completely HAYWIRE! - at times it appears as though the frequency
of the display has been fipped up a notch - its that bad!
For your infomation (in case anyone can help further) I'm using the
machine with a T.V. that has both RF and AUDIO/VIDEO connections, so I
have tried both the RF and MONITOR sockets and I get the same problem
through either.
Does that point towards a problem on the PCB?
I'd be grateful for any more information/help you can give.
Mark.
|
| 1118.6 | check modulator also! | UFHIS::BFALKENSTEIN | | Tue May 14 1991 12:56 | 20 |
|
... sounds familiar. I tried to extend my monitor cable once, and got
exactly the same symptoms. I put back the original cable but the
problem stayed. Reseating the shifter and resoldering it's socket was
one part of the deal, a bad ground connection of the cable was the
other one. In your case, using a TV, try out a shorter cable and/or
check it's shielding. Try another TV to eliminate this one as a
problem source. Check the cage around the shifter for good ground
contact and that it is well closed. Are the any frequency emitting
devices around?
I still have some problems like your's in a less dramatic way, but
this is because of a RAM upgrade which uses some signals from the
shifter socket via ribbon cable. This cable leaves the cage and moving
it back and forth changes the display as well. I found the best spot
to fix the cable, so I have to live with the rest of a shakey display.
But, you don't have any RAM upgrade so I bet it's bad contacts or
signal shielding.
Bernd
|
| 1118.7 | A theory, probabally wrong | PRNSYS::LOMICKAJ | Jeffrey A. Lomicka | Tue May 14 1991 13:43 | 10 |
| I now suspect undershoot due to impeadance mismatch between the systems
or in the cable, which is being interpreted by the TV as a sync pulse.
Undershoot would be greater for long durations of white signal, thus the
reason it get's worce for larger windows. Extending the cable would
cause this, especially if audio cable was used to carry the video
signal.
However, this theory does NOT explain why it does it for both RF inut
and MONITOR input...
|
| 1118.8 | Try moving the screen to a different location! | BAHTAT::REID | | Tue May 14 1991 13:59 | 9 |
| My system gave similar screen shakes. It started after I had moved the
machine for a weekend. When I put it back I got the shakes on the
screen, the bigger the window the worse it got. I discovered that
moving the monitor away from the system made it go stable again. It has
never done it since even if I put the monitor back where it was before.
You never know it could be worth a try!!!
Regards
|